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 СообщениеДобавлено: 29 июн, Вт, 2010, 16:53 
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Ничего общего, забудьте о фростборне, он здесь вообще не при чем.
Фростборн это обесцвеченные, временно, кончики шерстинок, что создает этот эффект.
А я пишу о мозаицизме на серебре.

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- А почему с топором?
- Вы мало знаете о добрых феях.


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 СообщениеДобавлено: 29 июн, Вт, 2010, 16:59 
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У меня вопрос все-таки почему не руфизмы... Как вы их отличаете?

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Что толку, если ты сразу окажешься на вершине горы? Ты увидишь только облака. (китайская народная мудрость)


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 СообщениеДобавлено: 29 июн, Вт, 2010, 17:00 
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мож не в тему, но нам вот тоже "диагноз" мозаицизм поставили

Изображение

если не понятно - обведу потом куда смотреть

кошка сама рецессивного окраса, да еще и это до кучи вылезло...

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 СообщениеДобавлено: 29 июн, Вт, 2010, 17:30 
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У нас был котенок (кот) с таким перецветом,от ОверЛорда и Регины (кошка от лиловой матери и затушеванного отца).К сожалению,показать мне нечего,фотки если и сохранились,то в каких-нибудь забытых архивах,котенок был продан под кастрацию,владельцы не проявлялись.На тот момент (от рождения и до 3-х с небольшим месяцев) честно считала,что это руфизм.Но вот именно так - как двухцветная маска,разделяющая мордаху на 2 части по вертикали.Больше такого "чуда" не рождалось.

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 СообщениеДобавлено: 29 июн, Вт, 2010, 17:39 
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Шоколадкина писал(а):
У меня вопрос все-таки почему не руфизмы... Как вы их отличаете?

Потому что руфизмы видела неоднократно, они в принципе другие.
Руфизм, прежде всего, не имеет четких границ, затрагивает не только фон но и сам рисунок, т.е. общее какое-то порыжение всего где он есть.
Руфизм имеет свойство становиться ярче с возрастом, в ясельном его практически нет, а тут с рождения и очень ярко.
Руфизмы как налет,т.е. внутри есть серебро, а тут куски фона вообще не имеют серебра.
Ну и последнее - руфизм это дефект гена Агути, а у моих дефект гена серебра (I)

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- Я добрая фея!
- А почему с топором?
- Вы мало знаете о добрых феях.


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 СообщениеДобавлено: 29 июн, Вт, 2010, 18:11 
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Не знаю, что это, для руфизма слишком ярко, для мозаицизма слишком много

У меня был вот такой товарищ. Рос странненько. В младенчестве сверху жёлтенький, снизу беленький Потом желтизна ушла, стал вполне себе приличный кот. Последняя фотка в 8 месяцев. Сейчас нормальное серебро.

Изображение

Изображение

Изображение
Изображение


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Ну вот и мне так подумалось,что это какой-то сбой в действии ингибитора.

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Мозаики - лентиго по сути.

Бивает сбой в ингибиторе, бывает в красном, бывает мозаицизм глаз, бывает тебби-нетебби.

Особенно заметен на красном - синие усы, серые губы и пятки у рыжих всем почти знакомы...

щас стаьтю дам

только переводите сами, мне и так по приколу почитать было

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MOSAICISM, TORTIE TOMCATS, GENETICALLY IMPOSSIBLE KITTENS AND GENDER ANOMALIES
1996, 2003 Sarah Hartwell
When this article was originally written (1996), I had heard from a breeder who owned a fully fertile tortoiseshell and white stud cat. She wanted to know why he only passed on the gene for red and never for black. Her stud turned out to be a red-and-white bicolor mosaic (meaning a somatic mosaic). Since these mosaics breed as for bicolors, his black hairs were not inheritable - they were the equivalent of moles in humans.
Originally, tortoiseshell tomcats were believed to be XXY individuals (this is explained in more detail later on) which accounted for them being infertile and having "female" colouration. Some also behaved more like females and this was also attributed to their XXY genetic make-up. With genetics testing still in its infancy, and too expensive for use with pets, the other conditions now known to cause tortoiseshell males were not recognised or understood.
In earlier feline genetics texts, mosaic was defined as a genetically red/red-and-white (or dilute of these) cat which has patches of black hairs so that it appears to be tortoiseshell/calico. The black patches (or hairs) are not genetically inherited; they are caused by localised mutation of skin cells in the embryo (somatic mutation). The mutant skin cells produce black pigment. This form of mosaicism was once thought to account for many of the fertile 'tortoiseshell' males since test matings showed them to be genetic reds/red-and-whites. It also occurs in females, but is mistaken for normal tortoiseshell.
As genetics knowledge has advanced, the terms "mosaic" and "mosaicism" have been (and often still are) used to mean different things. Some texts use "mosaic" to mean the outward appearance, regardless of the cause while other texts use mosaic to mean a genetic effect which may or may not be visible. To avoid confusion, I have tried to keep to a consistent set of definitions e.g. somatic mosaic, XY/XXY mosaic.
The discussion of cats with unusual chromosome complements (XXY, XYY etc) brings us on to gender anomalies which is a fascinating field in itself. I have expanded this article to include these in the second part of this article. Many of the listed anomalies have not been documented in cats, but their existence in other mammals means there is a probability that they do occur in cats. Gender/fertility problems are only usually investigated in pedigree cats in breeding programs. In the random breeding feline population (60-90% of pet cats, depending on where you live) such anomalies are likely to go unnoticed.
Definitions
Part 1: Tortoiseshell and Calico Tomcats
How Common Are Tortoiseshell Tomcats?
The Gene For Ginger
X Chromosome Inactivation
Somatic Mosaics, Klinefelters and Chimaeras
More About Mosaics
Mosaic Albinos
Germ Line Mosaics
Considering Chimaeras
Ranger, the Mosaic Lion
Freemartins
Human Chimaeras
Part 2: Sex Determination in the Embryo
Genetic Sex
Gonadal Sex
Phenotypic Sex
"Brain-Sex"
Normal and Abnormal Embryos
Chromosome Abnormalities
Gonadal Sex Abnormalities
Phenotype (Outward Appearance) Sex Abnormalities
Summary: Many Forms of Mosaicism
Case Study: Brody - male tortoiseshell klinefelter giant
Cats of Many Colours!


DEFINITIONS
Allele: there are different variants of most genes; these variants are properly known as alleles (for simplicity I use "gene" throughout this article).
Autosome: any chromosome other than the X or Y "sex" chromosomes.
Genotype: the genetic make-up of an organism.
Phenotype: the outward appearance of an organism (several different genotypes may result in the same phenotype).
Dominant: most genes are inherited in pairs; the dominant gene of a pair is the one which is physically expressed.
Recessive: the recessive gene is only physically expressed if both genes in a pair are the same recessive gene.
Hermaphrodite: having the sex organs of both male and female.
Intersex: Having undifferentiated sex organs, which are neither fully male nor fully female, but intermediate between the two.
Mosaic (1) having a coat with multiple colours e.g. brindle or tortoiseshell; (2) an individual whose cells have different genetic composition e.g. XY/XXY; (3) having somatic mosaicism.
Somatic mosaicism the presence of genetically distinct populations of somatic cells in a given organism due to DNA mutations/damage or chromosome abnormalities.
Germ-line mosaicism a particular mutation early in the development of an embryo means that, later in life, some of the egg or sperm cells will carry the mutated gene which can be passed on to offspring. This will only be detected in offspring which inherit the mutation.
Chimaera an individual which developed from two genetically distinct germ-lines e.g. where two embryos fused in the womb. Scientists have created a deliberate chimaera by mixing sheep and goat embryos; this "geep" had some goatlike body parts and some sheep-like body parts (in fact it looked like a goat's legs had been stitched onto a sheep body!).
A single individual can have more than one form of mosaicism. The fraction of cells having each genotype is quite variable, reflecting how early during embryo development the mosaicism originated. While mosaics and chimeras both have more than one genetically-distinct population of cells and the outward appearance may be identical, there is a clear distinction between mosaicism and chimaerism. In mosaics, the genetically different cell types all arise from a single embryo, whereas chimeras originate from fusing more than one embryo.
Many parts of this text are deliberately simplified so they can be understood by those with no previous genetic knowledge. Readers may also be interested in the book "Cats are Not Peas" which is about George, a male calico.
PART 1: TORTOISESHELL AND CALICO TOMCATS
Every so often I am asked if a tortoiseshell or calico tomcat is valuable. You will find advertisements on the web, or in newspapers, placed by people hoping to sell a tortoiseshell tomcat for a large sum of money. One website even said that if you found a tortoiseshell tomcat, you could sell it for a fortune and retire!
Despite their rarity, tortoiseshell tomcats are not valuable in the financial sense. They have scientific value. Those that are fertile cannot pass on the tortoiseshell colour - you cannot breed more tortoiseshell males from them. As pets they are just like any other cat. As pedigree cats, there may be no colour class for them to enter so however fine they look, so they may be unable to win prizes (some breeds/shows have an "Any Other Colour" class). The abnormalities which have created a tortoiseshell male may also make him more susceptible to auto-immune disease or testicular tumours.
In short, if you have a tortoiseshell male cat, he is not going to make you rich! Even the minority of fertile tortie tomcats are not valuable in money terms because they don't breed true. So next time you see someone advertising a "rare tortie male" on Ebay, usenet or a bulletin board, you can wonder who is more gullible - the person expecting to make a fortune or the person who pays over-the-odds because they think the cat is going to make them a fortune!
Another myth about tortoiseshell male cats is that if an owner takes a tortie or calico cat to be spayed (quite reasonably believing it to be female) and it turns out to be a male which the vet then castrates, the owner is entitled to get the money back from the vet for unnecessarily neutering a cat which is already sterile. Even though a male calico is likely to be sterile, he probably still has the male hormones which make him spray. Many owners of tortoiseshell males like to mate the cat once to see if he is fertile. With so many unwanted kittens in the world, please don't do this unless you are involved in a genuine research programme.
To understand what creates tortoiseshell and calico males, we first have to look at the genes for red and for tortoiseshell. The white areas of calico cats are caused by different genes and will be ignored. The tabby pattern is also caused by other gene. In this article, "ginger" also includes "ginger-and-white" (red bicolour) and "red tabby" (with or without white). "Tortoiseshell" also includes "tortoiseshell-and-white" (calico) and "tortoiseshell tabby" (torbie) (with or without white). Cream is a dilute version of red. Blue (grey) is a dilute version of black.
HOW COMMON ARE TORTOISESHELL TOMCATS?
Over the years and from region to region, the figures given have ranged from 1-in-1000 to 1-in-many-thousands. Some of these would have been mis-dentified poorly defined classic tabbies, especially where white patches obscure the tabby pattern. Some breeds may be more prone to genetic gender anomalies than others (this has been noted in dogs, but there is currently no comparable data for cats).
According to Roy Robinson's 'Genetics for Cat Breeders' out of a total of 125 kittens produced by black female x orange male there was 1 tortoiseshell male. The majority of calico or tortoiseshell males studied in recent years are from tortoiseshell (with or without white) females and are XXY (Klinefelter) or XXXY (chimera) genetic make-up. Further studies in the early 2000s on the chromosome complement and histology (structure) of tortoiseshell males in the UK and USA indicated around 0.43% of chromosomally abnormal (XY/XY, XX/XY or XXY) tortoiseshell male cats in the UK and 0.033% in the USA.
In 1897 a tortoiseshell tomcat in Matlock, Derbyshire became famous not for its colour, but for having wings (the genetic condition Feline Cutaneous Asthenia). It was described in a local newspaper as ‘an extraordinary large tortoiseshell tom cat with fully grown pheasant’s wings projecting from each side of its fourth ribs'. The story was reported in the High Peak News of Saturday 26 June 1897:
"Extraordinary Capture at Winster: A Tomcat With Wings. [...]Mr Roper of Winster, while on Brown Edge near that village, shot what he thought to be a fox, which had been seen in the locality some time previously, on Mr Foxlow’s land. Thinking he had missed his aim, Mr Roper gave up the quest, but returning later he found he had killed the animal. It proved to be an extraordinarily large tomcat, tortoiseshell in colour with fur two and a half inches long, with the remarkable addition of fully-grown pheasant wings projecting from each side of its fourth rib."
In "Concerning Cats" (1900), Helen Winslow wrote There has been a newspaper paragraph floating about stating that a prize of several thousand dollars had been offered in England for a male tortoise-shell cat. This is probably not true, as a Mr. Smith exhibited a tortoise-shell he-cat at the Crystal Palace Show of 1871. Several tortoise-shell and white toms have been exhibited since, and one of these has taken nine first prizes at the Crystal Palace Show; but the tortoise-shell he-cat is extremely rare However, there may have been some confusion over what a tortoiseshell cat looked like as she went on to note that a real tortoiseshell "is not a striped tiger nor a tabby. It has three colors usually, black, yellow, and red or brown; but these appear in patches rather than stripes."
Another early report of a male tortoiseshell cats is a British Shorthair exhibited in early English cat shows (1900s). Lady Alexander's winning cats included Champion Ballochmyle Samson (left), an apparently tortoiseshell male. There is also a reference to Champion Tortie Man of Gallus. Frances Simpson, in "The Book of the Cat" (1903) describes the black-and-orange tortoiseshell and states "At the present time we have Lady Alexander's and Mrs Herring's males - 'Champion Samson' and 'Champion King Saul'." In the chapter on short-haired cats, a cat judge, Mr Jung, elaborates on these tortoiseshell toms: "One of the singularities of the breed is the nearly entire absence of males in every litter; in fact, I remember the say was that a tortoiseshell tom was as scarce as the dodo. At the present time however, we hve two good toms - viz. 'Champion Ballochmyle Samson,' winner of no fewer than twelve first prizes and championships, the property of Lady Alexander, and 'Champion King Saul,' winner of numerous championships and first prizes, owned by Mrs herring. Both these males are very good, and whenever they have been penned together it has always been a difficult matter for me to decide the winner. In females, 'Ballochmyle Bountiful Bertie' (sire, 'Ballochmyle Samson') ..." which means 'Ballochmyle Samson' was a fertile tortoiseshell male. The photograph shows him to be very definitely a brindled tortoiseshell.
Elsewhere, Simpson noted that tortoiseshell toms were rare, but stated "A number of clever fanciers and breeders have used their best endeavours and patiently persevered in the fruitless attempt to breed tortoiseshell male cats. In my long experience I have never known anyone who has succeeded, and those specimens that have been exhibited from time to time have been picked up quite by chance. I recollect, many years ago, at the Crystal Palace show, seeing the pen of a short-haired cat smothered with prize cards, and the owner of the puss standing proudly by, informing inquirers that it was a tortoiseshell tom that lay hidden behind his awards. This man had been paid a shilling by a London cook to take away the troublesome beast out of her area! He had taken it away to some purpose, and his surprise at finding himself and his cat famous was amusing to behold."
Interestingly, in 1912, a male Tortoiseshell and White was registered with the GCCF, being "Ballochmyle Bachelor", owned by Lady Alexander, bred by C Adkin, born 11th March, 1905, sire "Jabez", dam "Kit". He won 1st Prizes at the National CC Show in 1909, 1910 and 1911 and at Westminster in 1911 and 1912. There seem to have been several tortie males from the Ballochmyle line suggesting either some very interesting genetics in the Ballochmyle line!
Another early and famous tortoiseshell male was Poldhu in the 1950s, a male Cornish Rex sired by founding Cornish Rex stud Kallibunker. Poldhu was a blue-cream-and-white male who sired a number of kittens. There is controversy over whether Poldhu was truly a tricolour or whether he was a blue tabby (all photos from that time are black and white and show tabby markings). Poldhu was owned by the noted cat breeder Brian Sterling-Webb and had been examined by several geneticists who attested to the fact that he was a blue-cream. Because Poldhu was both tortoiseshell (blue-cream) and fertile, veterinarian Dr A G Searle took a tissue biopsy for research, something which would not have been done for a blue-tabby. This had the unfortunate side-effected of rendering Poldhu sterile. To add insult to injury, not only was Poldhu rendered sterile, the tissue sample was lost.
Some contest that Poldhu was actually blue-tabby-and-white (which contradicts the veterinarian's interest in getting a tissue sample). According to "The Rex Cat" by Phyllis Lauder, Poldhu sired red and cream females out of four different queens. He could only do this if his X chromosome carried the gene for red (diluted to cream by other genes). His owner, Mrs Ennismore, recorded that Poldhu sired red or cream females, but records apparently show that he sired blue tabbies out of a solid blue female. It seems most likely that Poldhu was an XY/XY chimaera (XY/XY chimaeras are described in detail later on).
Poldhu was not the only male tortie Rex. Mrs Roma Lund of Maidenhead owned a blue tortoiseshell Devon Rex called Ben. Though there were no details on his fertility, Ben was valued at £1,000 for his rarity. The account was undated, but appears to be 1970s when Devon Rexes were rare and expensive, whatever their colour.


Blue-cream (dilute tortie)

There has also, apparently, been a fertile tortoiseshell-point Siamese male in England who has sired a number of litters before being neutered. He bred as if a seal point (i.e. for black) and some reports have suggested he was a Champion, which is unlikely since there is no show class in which a tortie male can be entered. Unfortunately that report was undated, however back in the 1960s or 1970s a Van-patterned male longhair turned up in the USA. This cat had a blue spot on his head mingled with cream, a cream spot on his body and a blue tail. Blood and skin samples were sent to Pennsylvania University for chromosomal investigation. The University concluded that the tortoiseshell Van male would be fertile, which meant the blood and skin cells contained the normal XY complement. His sister was black, indicating a black father and tortie mother. In the 1980s there was a Dutch-bred dilute calico (blue-cream-and-white) British shorthair male called Benjamin's Jos Brink. This cat sired litters between 1982 - 1987.
One of the most interesting cases surely has to be the "Tripple" line of Norwegian Forest Cats. This line apparently produces fertile male calicos at least every third generation. The foundation male of this line was a fertile calico male called Tripple. Tripple had a black patch on his flank which may be a somatic mutation, but otherwise appears to be a red/white bicolour. Some of these calico toms could be seen at Dutch cat shows. They look like ordinary red or red bicolour males, but have small black spots - these spots are very definitely black, not merely dark red. Some also had a mix of red and black in their coat, with the red always predominating. Studies of pedigrees from Tripple's breeding line indicated that calico males occurred every third generation and sometimes as often as every second generation. There was apparently a distinct ratio of calico males which certainly merits a more detailed study of the phenomenon. Initial studies, based on phenotype rather than genotype, showed no evidence of XXY (Klinefelter) in the line.
A fairly casual surf of the internet and usenet (newsgroups) turns up a number of cases of tortoiseshell male pet cats, some identified as XXY make-up, including adverts offering rare male calicos for sale. Some reports must be taken with a large pinch of salt. For example a supposedly calico male called Bentley was described in 1992. The owner had no idea that Bentley was unusual until someone described Bentley as a "she" and then said that cats with tricolour noses were always female. Bentley's nose was white, black and beige. The fur on Bentley's side was a mix of black tipped with beige and solid beige. However, Bentley's owner added "the beige forms circles like bulls eyes on his sides" meaning that Bentley was not a genetic anomaly at all, but an ordinary classic tabby cat with an ordinary mix of agouti and non-agouti fur! One wonders how many "tortie toms" are nothing of the sort, except in their owner's imagination or because the owner is unfamiliar with the tabby pattern?
In 1992, Mindy Machanic reported a 12 week old male calico called Huggy Bear. The vet was initially dubious that the cat was male. Huggy Bear was white and black and red with a Van pattern: white body with one large black spot striped with light tan, white legs with a tiny black spot, a fluffy black tail, striped with light tan and a white head with black and red/reddish brown triangular patches in front of his ears. He was healthy and not at all retarded as initially feared; he was also developing some typically male behavioural traits. In 1994, Paul Atchley bred a litter of calico kittens including two male calicos which were mostly white with orange, black, and grey patches. Several other tortie males were mentioned in 1994, including one called Smudge that went missing for six weeks before being found in a ventilation pipe and a a 7 year old tortoiseshell male barn cat called Injun.
In 1996, a newsgroup posting referred to a calico male called Camille who was, quite reasonably, assumed to be a female when adopted as a kitten. Camille has wide hips, walks with a wide gait, is healthy and has a sweet temperament; traits suggestive of XXY chromosomes (Klinefelter). He sounds similar to Brody Baker whose case study is towards the end of this article. By contrast, in 2001, a very macho dilute tortoiseshell male, Toby, was reported on Usenet -his fertility was unknown, but even after neutering he tried to mate with other cats. In 2001, a large, sweet-natured dilute calico (blue/cream tabby + white) male called Calvin was reported. The owner was tempted to breed him due to his rarity. In 1999 another writer said that her mother had bred numerous tortoiseshells including 2 male torties, but to her disappointment both males were sterile. In 2002 a family of four stray cats were reported including a red longhair, a black shorthair, a tortie female and tortie (predominantly red) male - this covered most of the normal colour possibilities for the "O" gene plus the anomalous colour! In 2003, another posting reported an orange tabby female called Carrot who produced a male calico kitten in her first litter. Other reports sound like cases of mistaken identity e.g. on Sept 20th 2002, a shorthair tortoiseshell male cat coloured grey, black and white was impounded in Bismarck, ND, USA (though this could be a silver classic tabby and white).
Tortoiseshell males from pedigree breeds are perhaps the most interesting as these have complete genetic histories detailing the colours of parents and related cats. Riëtte van Beek has collected information on a number of tortoiseshell male cats, their parentage and their offspring (if they are fertile). In addition to the cases detailed above, these enigmas include Kapamba's Home Miracle (tortie-and-white Norwegian Forest Cat, fertility and genetic make-up unknown), Dar es Salaam's Varsha (male Seal-Tortoiseshell Point Birman who passes on red), and Norwegian Forest Cats from Abelia cattery (France): Patchouli (tortie and white, breeds as a red-and-white) and his full brother Santal's Neroli (blue-cream tabby and white, breeds as a blue tabby and white), both being fertile male tortoiseshells born in 2001.
THE GENE FOR GINGER
The ginger colour of cats (known as "orange" or "red" to cat breeders) is caused by the "O" gene. The O gene changes black pigment into a reddish pigment. The O gene is carried on the X chromosome. A normal male cat has XY genetic makeup; he only needs to inherit one O gene for him to be a ginger cat. A normal female is XX genetic makeup. She must inherit two O genes to be a ginger cat. If she inherits only one O gene, she will be tortoiseshell. If she inherits no O genes, she will be black.
One explanation is that some skin cells activate the O gene while others activate the gene in the equivalent place on the other X chromosome (more precisely, these are alleles, or variants, of the same gene). This occurs early on in the embryo and as skin cells multiply, they form patches. Another theory is that the cells activate and migrate across the embryonic skin surface. This is detailed in Tortoiseshell and Tricolour Cats. Either way, the skin is a mosaic of cells where some have the O gene active (converting black pigment into ginger pigment) and some do not (forming "normal" black pigment). This can only happen in cats with two X chromosomes.
Normal male cats only inherit one X chromosome so this is active in all skin cells as there is nothing equivalent on the Y chromosome which could "switch off" the O gene. More rarely there are male cats with XXY genetic make-up (equivalent to human Klinefelter's syndrome). These turn out male because they have a Y chromosome. However, just like XX females, they undergo X-inactivation and are genetically mosaics. If only one of those X chromosomes carries the O gene, this can result in a tortoiseshell tomcat.
Mating together a red male and a red female can never give a tortoiseshell because the cats can only pass on the "O" genes to their kittens. However a tortoiseshell female called Royal Mainly's Otylia turned up in such a mating. Otylia has a small black patch on her ear, probably the result of a somatic mutation. Although tortie is normal in females, Otylia was a "genetically impossible kitten" because neither parent had a gene for black. In the random-breeding population, similar genetically impossible females go unnoticed because the paternity of the kittens is unknown.
The O gene is called a sex-linked gene because it is carried on a sex chromosome. The different outcomes of mating red cats, black cats and tortoiseshell cats (and the different kittens these matings produce) are given in tables in Tortoiseshell and Tricolour Cats.
Sometimes the description of how the O gene works becomes garbled. A newsgroup poster wrote "Male calicos are quite rare, because the gene that produces calico colouring is usually lethal in utero to male foetuses (the technical explanation's a bit complicated, but you could look it up in any good book on cats). This doesn't mean a male calico is highly valuable. For one thing, a true calico male is usually sterile, so it can't be used to breed a line of 'pure' calico cats." An explanation from 1992 said "The calico male is probably triploid i.e. XXY which allowed the calico recessive to show." As I have already described, calico is an interaction of genes, it is not a single recessive gene.
X CHROMOSOME INACTIVATION
Almost all female mammals are mosaics i.e. a patchwork mixture of two genetically different types of cell although this may not have a visible effect. Females inherit 2 X chromosomes while men have an X and a Y chromosome (a gene on the Y chromosome makes an embryos develop as a male). While other chromosomes must be inherited in matched pairs, males get along just fine with only 1 X chromosome. This suggested that having 2 X chromosomes could cause some sort of genetic abnormalities (too many genes), but female mammals overcome that problem by inactivating one or other X chromosome.
It had long been known that the cells of female mammals contain something called the "Barr body" and that tortoiseshell cats were almost always female. In the 1960s, geneticist Mary Lyon suggested that females switch off one X chromosome in every body cell - the Barr body is the bundled up corpse of the switched off X chromosome. Very early in the development of female embryos, each cell inactivates one of its X chromosomes at random. Each of these cells eventually gives rise to a patch of cells in the adult female that has the same inactivated X.
Random inactivation means that a female mammal is a mixture of two different cell types. Some regions of her body use the X she inherited from her mother, the rest use the X inherited from her father. She is a mosaic of two cell populations. Since the X chromosome carries around 5% of her genetic material, those different patches can be genetically very different! In cats this is visible as tortoiseshell females - some X chromosomes give rise to red fur while others give rise to black fur. A similar effect is seen in human females with Anhidrotic Ectodermal Dysplasia (reduces the number of sweat glands in the skin). Where only one X chromosome carries the faulty gene, the skin becomes a mosaic of small areas of sweating and non-sweating skin which only becomes visible in certain conditions.
Although the effect of mosaicism may not be visible (or is only visible in tortoiseshell cats), the whole body is a mosaic of genetically different cells. This was demonstrated when CC the cloned kitten was born. Cloned from a tortoiseshell-tabby female, CC could have turned out either red-tabby or brown-tabby (the white patches are caused by a different gene), but not tortoiseshell tabby. Nature's equivalent of clones are identical (monozygotic - coming from a single egg) twins. X chromosome inactivtion means that female identical twins may turn out to be very different and at the genetic level, they are not truly identical.
It is possible (though statistically unusual) for an embryo to use one X chromosome almost to the exclusion of the other. In female cats this can lead to genetically tortoiseshell females appearing to be wholly black or wholly ginger, but having unexpected black, ginger or tortie kittens. In apparently solid ginger or solid black females there be other coloured fur present, but it may be one or two hairs only - the equivalent of a needle in a haystack. If the cat also inherits the white spotting gene, those other coloured hairs may be obscured by white patches.
SOMATIC MOSAICS, KLINEFELTER AND CHIMAERAS
According to leading cat geneticist Roy Robinson there were three possibilities which can cause tortoiseshell tomcats: somatic mutation (sometimes termed mosaicism), Klinefelter syndrome and chimaerism.
Somatic mutation causes ginger cats to have small black spots, much like moles or birthmarks in humans. Occasionally, these black blemishes may be large enough to give the appearance of a tortoiseshell cat, albeit one with a low amount of black. The size of the black patches may also depend on how early in embryo development the mutation happened. Very late and it gives a spot or speckle. Where it happens earlier, the black patches are larger as the cells multiply during embryo growth. Somatic mutation is rarely noticed in female cats because tortoiseshell is an unremarkable colour of females - it may be noticed if a black or tortoiseshell female kitten appears in a litter where black or tortoiseshell is a genetically impossible outcome of the mating. In ginger-and-white cats where there is a lot of white, the addition of even small black patches can give the appearance of a calico cat.
Fernando of Canpaza is a cream-coloured German Maine Coon (born 2002) with two small blue spots on the top of his head which may be due to a localised mutation of skin tissue. Several breeders told Fernando's breeder, Elvi Weidemann, to neuter this unusual tomcat and sell him as a pet. However, a veterinary hospital in Hannover (Germany) is running a study project on tortoiseshell tomcats and Fernando has been included in this project. A blood test proves he is a normal XY male. Breeder and researchers were keen to see if Fernando could father kittens - and what colour he passes on to his kittens. In December 2003, I heard the results of Fernando's matings. He was mated with Roxanna a black-silver tortie resulting in 8 kittens weighing between 70 and 95 grams (smallish, not unusual for a large litter): 1 cream-smoke male (Bucky), 1 black-silver tortie female, 1 red tabby female, 3 red males, 1 black tortie female, 1 cream male and a black-silver tortie male. Sadly the latter 5 kittens died of a bacterial infection; the black-silver tortie being an especial loss. Fernando will have one further test mating before being neutered.
Another cause of tortoiseshell males is where a male has the abnormal XXY genetic makeup (Klinefelter Syndrome), but only one of those X chromosomes carries the O gene. The X chromosomes are randomly inactivated, just as in an XX female. These cats have usually been found to be sterile and their tissues may be a mixture of XX and XY cells, XX and XXY cells or XY and XXY cells! If some of the "normal" XY tissue occurs in the testes, then the cat might even be fertile although the colour of the offspring he sires depend on whether the X gene in the testes has the O gene or not.
In 1997, T Lehmann reported a calico male which was red, white, black and grey. The genetic explanation he was given was that male calicos are an anomaly resulting from a failure during meiosis (cell division which creates eggs and sperm) called non-disjuncture. The chromosome of a particular pair fails to separate so that the female donates 2 XX chromosomes instead of only one. If this is fertilised by a Y sperm it (usually!) produces a physically male animal.
In September 2003, I heard from Laura K Baker of Dublin, Ohio who owns a Klinefelter (XXY) calico male called Brody. Brody was saved from being euthanized at the vet where someone dropped him off as a scrawny kitten. He has feminine cat features and misshapen feet, but the primary distinguishing feature is that he is a Klinefelter giant and weighs over 25 pounds. Predominantly white, Laura describes him as shaped like a small sheep! In temperament he is intelligent and sweet-natured and very huggable. Brody needed some operations and special treatment as a kitten due to a broken hip and hates vets. His misshapen feet are apparently a birth defect. Vets are generally puzzled by him. Initially, the vet explained that Brody had Klinefelter's Syndrome and probably wouldn't live very long, or that he would be perpetually sickly if he survived long-term. Luckily both prognoses were wrong and possibly Brody is a mosaic of XXY and either XX or XY cells which would explain his ongoing good health (many surviving Klinefelter individuals turn out to be mosaics). Although small and scrawny as a kitten, he ballooned up around age 2 and seems to get bigger every year.
Another Klinefelter tortoiseshell male is Simba von Schindetal an apparently solid red Maine Coon stud who failed to impregnate proven fertile females in 1988. Blood samples sent to a veterinary college in Giessen showed he had a mix of XY and XXY cells. A detailed physical examination of Simba found a small black spot on his left ear and a few black hairs sprinkled in his fur. These were originally thought to be harmless somatic mutations.
Fertile male tortoiseshell cats often have abnormal ectodermal tissue (XXY), where the skin comes from, while maintaining normal mesodermal and endodermal tissue (XY). This is not to be confused with "black" hairs appearing in an otherwise red coat in some lines of Persian cats. These hairs are actually super-pigmented with phaeomelanin (red) and not eumelanin (black).
It is even possible for 2 fertilised eggs to fuse. If the two fertilized eggs (embryos) are both XY, this gives an XY/XY male chimaera. In an XY/XY chimaera if one X has the O gene and the other does not then some fur will be ginger and some black because different parts of the skin originate from different eggs! It could also be a mix of any other colours found in male cats e.g. a mosaic of grey and black. An XY/XY chimera would be fully fertile.
If an XY egg fuses with an XX egg (a male embryo fuses with a female embryo), it gives a XX/XY chimaera containing some tissues/organs which are genetically female and other tissues which are genetically male. In an XX/XY chimaera, X chromosome inactivtion will occur. The 3 X chromosomes in the animal may contain an assortment of different colour genes (especially if the mother mated several times and the eggs were fertilized by different fathers). The physical appearance and the sexual behaviour of an XX/XY chimaera depends on which structures contain which chromosomes. A good example of this is the now famous Maine Coon Solkatz Pretty Boy Floid who is a mix of red, grey and white - a colour combination impossible in a normal XY male.
Until recently it was believed that chimaeras were normally only produced in the laboratory and usually involved chimaeras made from different, but closely related, species. The geep is an interspecies chimaera mixing a sheep and a goat. Unlike a sheep/goat hybrid, the sheep/goat chimaera did not look like something halfway between the two species. The sheep and goat tissues retained their individual appearance, creating an animal with hairy goat-like legs and a woolly sheep-like body. Rat/mouse chimaeras have also been made. Increasing use of genetic tests on anomalous animals (e.g. those with genetically impossible colours, ambiguous gender) is revealing a surprising number of natural chimeras in the cat population and may account for more tortoiseshell males than previously thought. For example, chimerism is found in cattle. When a cow has twins, they almost always share a circulatory system. Blood stem cells from one embryo end up in the other embryo and both twins end up as chimaeras (microchimaeras).
Possibly the most famous tortoiseshell male cat is Solkatz Pretty Boy Floid, a pedigree Maine Coon, born Nov 1996 in Bremerton, Washington, USA. Floid is a triple genetic anomaly: calico male, mixed dilute and non-dilute colours and fertile! Floid was initially thought to be a dilute calico male (blue, cream and white) which in itself is unusual enough. However, the cream portions of his coat turned out to be red i.e a non-dilute colour. This is also very unusual as the dilution gene which gave him the blue (grey) colour should have converted all red portions into cream. Finally, Floid is fertile. Floid is a chimaera - the result of two fertilized eggs merging into a single embryo. On a genetic level, different portions of his coat (of his whole body in fact) actually belong to different cats. Although a very nice Maine Coon and the sire of some excellent offspring (none of which are dilute, therefore his testicular tissue is from non-dilute-carrying cells which also formed the red patches), Floid himself was unable to win titles because there are not colour classes for tortoiseshell male cats.
Are there a disproportionate number of tortie males in the Maine Coon breed? Another tortie male, Koonikki Feirfiz Geezabird (Geezer), had intersex traits - testicular tissue in the position of an ovary plus one normally descended testicle. Geezer reportedly had both male and female behaviour and the vet believed him to be XXY. Like Skipper (reported below), he solicited other males to mate him, but he also attempted to mate females. His father has since sired another tortie male (tortie tabby from a brown tabby female) so possible the father is producing aberrant XY sperm. A third tortie Maine Coon, Stormwatch Maxwell, was reported in 1997. Sired by a black smoke, Maxwell was mostly bright red, but had a black patch on one side of the face. Perhaps all the brouhaha over Pretty Boy Floid has simply made people more likely to report these unusual males.
Poldhu the fertile blue-cream-and-white male Cornish Rex from the 1950s may also have been an XY/XY chimaera; the main difference between Poldhu and Floid being that Poldhu had cream (dilute) instead of red (non-dilute).
Very occasionally, the tortoiseshell "male" is not male at all. It is genetically a female cat which, due to hormonal problems during embryo development, has developed the external characteristics of a male cat. This is the normal condition in female hyenas where the clitoris is elongated to form a pseudo-phallus and there is also a false scrotum. It is occasionally been reported in other animals which appear to be hermaphrodite, intersex or are masculinised females (genetic females which look like males). Depending on the cause, the false scrotum may contain fatty tissue or ovarian tissue. This may explain those cases of tortoiseshell "males" which act like females - they are genetically female with an external male appearance. These gender anomalies are discussed in more detail in a later section.
The case of Skipper (Hokkaido, northern Japan) was documented by zoologist Jeremy Angel in the 1980s. Skipper originally came from Sapporo. Angel noted that perhaps one in every one or two hundred tortoiseshells is a tomcat and that these were once prized by superstitious boat owners. In 1981, at one year and three months old, Skipper was described as looking un-tomcat-like. In head shape and general conformation, he more closely resembled a female. His genitalia were unambiguously male. He was calico with clearly defined patches of orange and black and unusually for the Japanese cats of the area, he had a straight tail, not a bobtail. His mother was known to be a longhaired calico, but his father was not known. Skipper's character was described as exceptionally calm and friendly and extremely fastidious in toilet habits. He did not spray and did not show any interest when his mother came into oestrus. When introduced to other cats, including full toms, in an enclosed colony, Skipper was curious, nonchalant and non-aggressive - and again, did not spray.
It was noted that other tomcats treated him as a female and attempted to mount him, This was initially thought to be dominance behaviour towards the newcomer. However, Skipper remained attractive to several of the tomcats and had no objection to being mounted. On some occasions he appeared to enjoy this attention and remained crouched and receptive, even after the other tomcat had dismounted. He also adopted the lordosis position and chirruped to attract his suitors. During summer, he was mounted frequently enough that his neck became callused (common in highly active oestrus females). Skipper's attitude to females was very different. By the time he was almost 2 years old, he still did not spray and still showed no interest in mating with females. On occasion he was aggressive towards females and frequently fought with them. Tomcats do not normally fight with females, particularly with oestrus females although females will fight among themselves. In this respect, Skipper's behaviour was female. He was always the instigator of any fight.
In 1982, Skipper showed signs of male behaviour. He stopped picking fights with females and began to show sexual interest in them. He also began to spray. Compared to a normal tomcat, his spraying and his sexual behaviour were half-hearted. Angel isolated Skipper with an oestrus female. Although not an enthusiastic suitor, Skipper mated her three times, but failed to impregnate her. Angel had intended to mate Skipper with other females to determine whether the cat was fertile, but an epidemic of cat flu claimed Skipper as one of its victims. Angel concluded that either Skipper was a slow starter or that he possessed an additional X chromosome which feminized his behaviour, this being the prevalent theory at that time.
Because, at different times, Skipper showed both female and male behaviour, he was possibly an XX/XY chimaera (external male genitalia but some internal structures, including his brain, being genetically female and causing female behaviour). A post mortem, which might have solved the puzzle, was conducted when Skipper died. Although his condition was assumed to be due to an extra X chromosome (XXY, Klinefelter Syndrome), this does not normally result in female behaviour in phenotypical male. However feminisation was once believed to be the norm and in 1997 a cat owner stated "Most calico toms are born infertile with a single testicle. We are currently in the process of having a calico tom checked to see if he is fertile. If he is he will have some sperm 'banked' before being neutered. He is white, tan/orange tabby patches, and light to dark grey spots (and a few stripes)." The only male calico encountered by his/her vet was a long time ago and very obviously a genetic error, since the cat was sterile and had numerous other problems.
In a comparable case, Rachel E Gibson wrote in 1997 of a male calico which only mated with a very sexually aggressive females and which aligned himself with the females more than the males. The other males treated him like a female so he may not have many male hormones. His behaviour corresponded with the theory of the time that XXY made tortie tomcats feminine in their behaviour. Boo, another calico male, was also believed to be sexually confused because of his extra chromosome. He attempted to mate with both females and males and also tried to nurse kittens or carry them around like a mother cat. Boo continued to spray after being neutered and was described as somewhat fat, not uncommon in XXY cats.
Somatic mosaicism and chimerism aren't restricted to red or red-and-white cats; it's just that we are more geared up to looking for elusive fertile tortoiseshell males and tend to overlook the fact that some apparently normal tortoiseshell females may be due to genetic abnormalities. Mosaics which differ from the usual patterns are also noticeable. Also in Japan in the 1980s, there was an instance of a beautiful grey-black-white fertile male (Panda). Like Floid, Panda (born 1978) was probably an XY/XY chimera (2 fused male embryos) as he had a mixture of dilute (grey) and non-dilute (black) in his coat. His father was a solid grey cat (Mo) and his mother was Aya (tabby-and-white). The colony into which he was born was inbred with more then 70% of the cats carrying Mo's genes. In addition to his odd colouration, Panda was born with a deformed tongue and could not suckle, so was hand-reared.
Some parts of Panda's body also appear to display a higher degree of white than others. The effects of the white spotting gene are discussed in Beautiful Bicolours - Tuxedo and Magpie Cats.This cat had normal male behaviour and was "very fertile". He would have bred as either a black or a blue (grey) cat depending on which embryo's cells hade formed his testicular tissue. The pelt diagram, based on a number of photographs (therefore not 100% accurate), gives some idea of his mosaicism.
In many cats, these forms of mosaicism will never be noticed because they naturally have black somewhere in their coloration; when the black is quite unexpected and defies logic then mosaicism is assumed.
MORE ABOUT MOSAICS
All female mammals are mosaics due to X chromosome inactivation. There are other forms of mosaicism where the different genotypes are due to a mutation or abnormality occurring in a cell of the embryo. As the cells multiply, some parts of the embryo are built from the normal cell and other parts are built from the mutant cells. Although all parts of the embryo come from a single fertilized egg, that egg has given rise to 2 slightly different populations of cells.
Mosaicism (somatic mosaicism) is more common and better understood than chimaerism. Mosaics occur when a mistake during cell division in the early embryo stops the correct number of chromosomes segregating to each cell, or creates a mutation in a single gene. Where this happens in one of the first few cell divisions after fertilisation, a large proportion of cells will inherit the mutation or chromosomal anomaly.
For example, some mosaics have patches of cells that have an extra chromosome (called trisomy). The individual develops trisomic patches of tissue - an XY male may have some XXY tissues (another potential cause of tortoiseshell male cats).
Mosaicism and X chromosome inactivation means that female identical twins never carry exactly the same genes. At a genetic level they are not identical! When an XX embryo splits in two, the two embryos follow their own developmental paths. The random nature of X inactivation in the two embryos can create startlingly different individuals. One female twin is colour blind or haemophiliac and the other isn't (these traits are carried on the X chromosome).
It is statistically unusual for the differences to be so extreme or for embryos to use one X chromosome almost to the exclusion of the other. In female cats this can lead to genetically tortoiseshell females appearing to be wholly black or wholly ginger, but having unexpected black, ginger or tortie kittens. The occurence of such genetically different twins leads researchers to suggest that it is X chromosome inactivation which triggers some cases of twins. X chromosome inactivation occurs early on and researchers suggest that an early split ensures that one embryo inherits the lion's share of good cells (having activated the more healthy X chromosome) while the other may not survive at all (comprising cells which activated the damaged X chromosome). Possibly an area of genetically less healthy cells is ejected (but continues to develop) to ensure that the other cells develop into a viable individual.
The usually invisible mosaic nature of females is suggested as the cause of auto-immune diseases; diseases where the body turns upon itself. Autoimmune disease occurs when the immune system treats part of the body as foreign tissue and attacks it. Since some auto-immune diseases are more common in females, it could be that immune cells commanded by one particular activated X chromosome are attacking body cells where the other X chromosome is activated. XXY (Klinefelter) males also seem prone to autoimmune disease.
Chimerism is less readily apparent in females. However this female tortie-and-white is a black-cream-white tricolour - an impossible colour combination. Black is a non-dilute colour, cream is a dilute colour. A normal tricolour would have been black-red-white or blue-cream-white because the dilution gene acts on both colours in the coat. To have a mosaic pattern of both black and cream, she would have to be a chimera of a black (non-dilute) embryo and a cream (dilute) embryo. Since she seemed structurally normal when spayed, both embryos were probably female. This is one of two black-cream-white females (both blue-eyed, but not colourpoints) I have seen.

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Mosaic Albinos
Another different type of mosaicism was reported in a shaded cameo Devon Rex kitten. The cat had golden eyes but was photosensitive, he remained scrawny and suffered chronic eye and respiratory infections. Investigation showed that his immune system was very poor. After months of tests to find out what was wrong, the diagnosis of mosaic albino was made when it was noted that the cat's fur was growing progressively lighter in colour and he was becoming more light sensitive. He ended up almost pure white with a tiny amount of red on the edges of his ears. The eventual diagnostic symptom of his condition was that his scrotum was pure white. Any whole male with colour should have darker fur on the scrotum. The poor immune response was linked to albinism. The mosaic albino condition is found in horses but is uncommon in cats.
Germ Line Mosaicism
Early in the development of an embryo, the cells that will give rise to sperm or egg cells in adulthood become separated from the rest of the developing embryo. These are known as germ cells and the cells set aside are called the germ line. Mutations in germ line cells rarely affect other body cells (somatic cells), but the mutation can be passed on to offspring though eggs of sperm which arise from those mutant germ cells. Thos mutations will become part of the offspring's DNA and can be passed on to future generations. Where some germ cells are affected and others are not, this is called germ line mosaicism or gonadal mosaicism.
For example, a mutation might occur in the germ cells which go on to produce sperm and the stud cat sires kittens which are 'genetically impossible' according to his own coloration or type. One example is that of Treker, Bonnie Arnold's normal-sized Persian stud who sires a proportion of miniature Persians due to a mutation in the sperm-producing cells. Although his mosaicism is not visible, Treker's sperm-producing cells are a mosaic of cells some of which have the gene for normal size and others with the dominant gene for miniature size. Offspring which inherit the gene for miniature size grow into miniature cats; because the gene is part of their DNA they can pass it on to their offspring.
Ranger, the Mosaic Male Lion
A partly black lion was born at Glasgow (Scotland) zoo. His colour was probably due to somatic mosaicism since black is not a colour observed in lions. This lion had a pitch black patch on a foreleg and across his chest. Called "Ranger", he was born at Glasgow Zoo in about 1975, the offspring of some lions acquired from Manchester's Belle Vue Zoo. At birth, he exhibited a melanistic patch which stretched from his right paw, all the way up the inside of his leg and across his chest. It was believed to be the first time melanism, even partial melanism, had been recorded in the African lion (apart from anecdotal cases).
Ranger (he was sponsored by Glasgow Rangers Football Club!), frequently mated but failed to impregnate a proven fertile female. Zoo staff believed he had a chromosome abnormality causing him to be sterile. Due to age and illness, Ranger was put to sleep in 1997 and his body was sent for post mortem at Glasgow Vet School. It was hoped that blood samples could be tested for the suspected chromosome abnormality, but it was not possible to get testable blood samples from the body. It would have been sensible to analyse tissue samples from the black area and golden area. A sample of testicular tissue should very definitely have been tested!
The pathologist believed that the melanistic patch was similar to that sometimes seen in domestic cats and which also results in sterility. However it is not the melanistic patches (somatic mutation) which cause sterility in domestic cats and Ranger is unlikely to have been XXY (which does cause sterility) because black is not seen in lions. The black patch on his fore-quarters should have had no effect beyond the affected cells though possibly Ranger's mutation also affected internal tissues, including the testes. If the testes had been affected then Ranger might possibly have sired black cubs (and even tortoisehsell female offspring!) had he been fertile.
CONSIDERING CHIMAERAS
In mammals, chimaeras are usually only identified when there is a mismatch between the chromosomal sex (XX or XY) and the genitalia. This can come about through investigation of an illness or through visual clues such as tortoiseshell coats in male cats.
In an experiment done with white mouse embryos, cancerous mouse cells were injected into the embryo. During foetal growth the cancer was somehow tamed and the effect of the cancerous cells was to produce black patches in the otherwise white mice (uninheritable since they were cell mutations, not inherited through genetics).
Freemartins
Chimaeric cattle are not at all rare. When a cow has non-identical twins, the circulatory systems of the two embryos almost always joins together. Blood stem cells from one embryo end up in the other embryo. Both animals end up as chimaeras (microchimaeras). Where one is female and the other is male, the female embryo is exposed to hormones from the male. This causes the female embryo to be masculinised. These are called freemartins. The look female and have infantile external genitalia with underdeveloped internal sex organs, but are infertile. Freemartins occur in other species, but less often. It is a a peculiarity of cattle that the blood supplies of non-identical twin embryos join together.
Human Chimaeras
Human chimaeras also occur. A boy born in 1994 (and reported in 1998) turned out to be genetically two people. Two fertilised eggs had fused into a single embryo. One egg was XX (female) and the other was XY (male), making some parts of his body genetically female while other parts were genetically male. He was outwardly male, but had a partial womb, fallopian tube and ovarian tissue. Others are less easy to detect, such as a woman who had some XY (male) blood cells. This can happen where non-identical twins share a blood supply in the womb and blood stem cells can migrate from one to the other.
Another human chimaera apparently occurred when an unfertilised egg divided into two. One of the cells was fertilised, the other wasn't. The unfertilised cell contained only the mother's chromosomes, which it duplicated. The fertilisation of the other cell meant the embryo could develop normally and a single XX/XY embryo was formed. Some of the boy's tissues contain only the maternal chromosomes while other tissues contain maternal and paternal chromosomes. A similar scenario occurs when a fertilized egg fuses with an unfertilized egg. In both cases, some tissues contain only maternal DNA and the cause was once believed to be parthenogenesis (the tissues tested were those derived from the unfertilized egg/cell).
In 2003, DNA tests (for kidney transplants) showed that a Boston, USA woman known as "Jane" was not the biological parent of two of her three naturally conceived sons. Her sons underwent blood tests to see if they were compatible kidney donors, but the results showed that two of them did not have any of Jane's DNA, although their father was Jane's husband and they did have his DNA. Initially, doctors thought Jane had undergone fertility treatment using donated eggs or her sister as a surrogate mother. However, Jane's ovaries were found to contained two different sets of genes. One of her sons came from one set of cells, while the other two were derived from the other set of cells. Jane is a tetragametic chimera , one of only 30 reported cases, and is made up of 2 genetically different populations of cells. This occurs when non-identical twin embryos, both female in Jane's case, fuse into a single embryo in her mother's womb. Jane's body contains 2 distinct types of DNA: "her own" cells and "her twin's" cells. Cells from one twin dominate in her blood, but her thyroid gland, mouth and hair carry the other twin's DNA, while cells of both types coexist amicably in her ovaries. Jane's case was reported in The New England Journal of Medicine (Vol 346).
Nature reported a similar case in 1979, when genetic tests suggested that a woman could not be the mother of any of her four children. Again, there were no previous suspicions that the woman was a chimera. In 1978 or 1979 a British tabloid newspaper carried a front page story of a woman who "carried her dead twin in her bloodstream". Although sensationalised, this was another instance of chimerism. The report carried several sensational claims including feeling the lost twin moving within her and blaming it for mood swings! In a case where chimerism is not yet confirmed, doubts were cast on a child's maternity in court during 2003 when a woman sued her partner for child support. Tissue-typing tests have shown that the partner is the father of the child, but that the woman is not the mother. Her case may prove similar to that of Jane.
The incidence of human tetragametic chimerism may be on the increase due to modern fertility treatments that cause women to release multiple eggs or that implant multiple embryos in the hope that some will grow. In 1998, the University of Edinburgh, UK reported a chimeric IVF baby resulting from the fusion of a male and a female embryo (The New England Journal of Medicine, Vol 338). Though outwardly male, the left hand side of his internal reproductive system had developed as female (presumably the child born in 1994 and noted earlier).
Although most of the cases cited above are females, it is possible for a man to be a chimera and for his blood and his testes to contain different DNA, confounding the results of paternity tests on his offspring.
Around 30 similar instances of human chimerism have been reported. Some are identified because they have sought fertility treatment or they required DNA testing or tissue matching. It is not known how common tetragametic chimerism is in the population since there are often no outward signs, especially where same sex embryos have fused (a few might have visible pigmentation mosaicism). One girl was discovered to be a chimera because she had one brown eye and one hazel eye. Others are detected when doctors investigate reproductive problems. A few might demand paternity tests, for example where a child has "impossible" characteristics such as a brown-eyed child born to blue-eyed parents. Many, if not most, chimeras will never discover their unusual origins and will go through life unaware of their condition.
There is also increasing evidence that most people are microchimeras i.e. contain cells from their mothers and older siblings. During pregnancy, the blood of the mother and foetus are kept separate, but the placenta is an imperfect barrier and some cells slip through. Children pick up some cells from their mother and she picks up some foetal cells. 80-90% of women carry their children's cells or DNA in their blood during pregnancy and up to 50% carry them for decades after giving birth. Some of those cells may slip from the mother's bloodstream into the body of the next child. Some cells may even pass from her children into her grandchildren. For some reason, our immune systems tolerate these cells in the blood and it may be an essential part of preventing rejection of the foetus. Some of those maternal cells may become incorporated into the body tissues of the foetus (where they may be associated with autoimmune disease although no firm cause-and-effect has been established).
PART 2: SEX DETERMINATION & DEVELOPMENT IN THE EMBRYO
Normal sexual development of mammals is a 3 stage process: establishment of chromosomal (genetic) sex; development of gonadal sex and development of phenotypic sex.
Genetic sex means whether or not the individual has inherited a Y chromosome. In cats (and most mammals), XX = female and XY = male. Other combinations occur and are considered abnormal.
Gonadal sex means whether the embryonic gonad develops as testis or an ovary. Embryo gonads are programmed to become ovaries unless the genes instruct them to become testes. Some of the genes with instructions for making testes are actually on the autosomes not on the X or Y chromosome. In some cases, genetic changes in the embryo's gonadal cells or developmental abnormalities will cause the embryo to develop inappropriate or abnormal gonads for its genetic gender. "Ovotestes" are undifferentiated gonads which have not (or not yet) become ovaries or testes.
Phenotypic sex means making the outward appearance of the embryo male. Unless instructed otherwise, the embryo will be female in appearance. If a Y chromosome is present, this causes production of hormones which cause the embryo to build male internal and external structures. Hormonal abnormalities at this stage can mean a male embryo fails to respond to these hormones and appears to be female or that a female embryo can turn out appearing male (and various intermediate stages).
Chimeras are individuals composed of cells which come from different embryos. Mosaics are also composed of two or more cell populations, but the cells all originate within the same individual. In both cases, the different cells can contain different mixes of X and Y chromosomes. The gonadal sex of chimeras and mosaics depends upon the proportion of XX cells and XY cells present in the indifferent gonad at the time when gonadal sex determination happens. It also depends on whether those cells are able to form a functional testis or ovary. The type of gonad formed then determines the phenotypic sex i.e. whether the individual looks male, female, neither or both.
"Brain-Sex": In a mosaic or chimaera, the brain might be masculine or feminine depending on which cells it arose from (there is evidence that male and female brains are wired differently). If the brain and the gonads developed from different cell populations, the brain-sex of an individual might not match its apparent gender. For example, an individual which looks male might have female behaviour because its brain is mostly female. If there have been developmental abnormalities a genetic female might outwardly appear to be male or vice versa. Some tortoiseshell male cats might behave like females because genetically they are females or because the cells which formed the majority of their brain are XX while the cells which formed their gonads are XXY or XY.
Normal and Abnormal Embryos
A normal sperm cell carries either an X chromosome or a Y chromosome. A normal egg cell only has one X chromosome. These meet up to form either an XX (female) or XY (male) embryo.
Sometimes an egg is abnormal and contains either XX or no X chromosome. When fertilized by a normal sperm it becomes XXY, XXX or XO (YO will not develop). It might also be fertilized by an abnormal sperm (see below).
Abnormal sperm can be XX, XY, YY or O (O means no X or Y at all). If one of these sperm fertilizes a normal egg it can produce XXY, XYY, XXX or XO. If it fertilizes an abnormal egg it will produce XXXX. XXXY, XXYY etc. In humans, mental retardation is often found when there are 4, 5 or 6 X chromosomes present.
The frequency of these abnormal conditions in cats is not known.

CHROMOSOME ABNORMALITIES
Chromo-somes Name Details Identified in Cats?
XO Turner's Syndrome (monosomy) Majority of "pure" Turner's indviduals die before birth. Surviving Turner's individuals usually XX/XO mosaics with a substantial fraction of normal XX cells.
Infertile. Underdeveloped genitalia. Small stature. ?
Might account for some infertile females.
XX Normal Female Female unless affected by developmental abnormality. Yes
XXX Triplo-X Varies. Some are normal appearing female, fertile. Others are sterile females. Often larger than normal stature.
XXY Klinefelter Syndrome Male. Sterile, underdeveloped genitalia, may develop some female appearance. Tend to be large and may have mild retardation. In mosaic form.
XYY Jacob's Syndrome Rare in the "pure" condition (mostly XY/XYY mosaics). Tall, fertile and apparently normal.
XY Normal Male Male unless affected by developmental abnormality. Yes
XX/XO Turner mosaic Surviving Turner's individuals are frequently XX/XO mosaics.
XX/XXY Klinefelter mosaic Appearance depends on which structures are XX and which are XXY. Yes
XY/XYY Jacob mosaic Apparently normal male. Seen in cattle: XY/XYY chimaeric bull (fusion of normal XY embryo and abnormal XYY embryo).
XY/XO XY-Turners
Mixed Gonadal Dysgenesis Appearance and behaviour depends on which parts are XO and which parts are XY. Phenotypically male, female or ambiguous genitalia.
YO Lethal YO eggs do not develop because many essential genes are carried on the X chromosome. N/A


GONADAL SEX ABNORMALITIES
Name Cause External Appearance Identified in Cats?
XX Male (Sex reversal) Either an autosomal trait or due to a Y-chromosome gene turning up on an autosome instead of on the Y-chromosome.
Genetically female, phenotypically male. Some testicular tissue in one or both gonads. Generally have male external genitalia (but abnormal in form) and are cryptorchid.
Internal genitalia: uterus, but other male or female internal structures may be absent.
XX True Hermaphrodite (Sex Reversal) Inerited as an autosomal trait or due to a Y-chromosome gene turning up on an autosome instead of on the Y-chromosome.
Genetically female, appear intersex. Some testicular tissue in one or both gonads. At least one ovotestis. The degree of outward masculinization is related to the amount of testicular tissue present.
Normal or abnormal female external genitalia e.g. enlarged clitoris (pseudophallus) or any phenotype in between these extremes. Possible. Hermaphrodite Burmese taken into cat shelter in Chelmsford, Essex (1996?) but no follow up. Not known if this was true or pseudo- hermaphrodite.
PHENOTYPE (OUTWARD APPEARANCE) SEX ABNORMALITIES
Name Cause External Appearance Identified in Cats?
Pseudo-hermaphroditism Chromosome constitution and gonads match up, but internal or external genitalia are ambiguous. See details below. See below. Possible. Hermaphrodite Burmese taken into cat shelter in Chelmsford, Essex (1996?) but no follow up. Not known if this was true or pseudo- hermaphrodite.
Female (XX) Pseudo-hermaphrodite Have ovaries but appear externally male or intersex due to masculinization of external genitalia.
Excess androgen while embryo developing. Has ovaries, uterus and vagina. Masculinization ranges from enlarged clitoris through to full external male genitalia with internal prostate.
Male (XY) Pseudo- hermaphrodite
(Failure of Mullerian duct regression ) Persistent Mullerian Duct Syndrome (PMDS) . Known to be autosomal recessive in some dog breeds. Female internal sex organs, external male appearance. May be fertile. May be monorchid or cryptorchid. An intersex condition that may be PMDS has also been reported in a Persian cat
Male (XY) Pseudo-hermaphrodite
(Failure of androgen-dependent masculinization) Androgen Insensitivity Syndrome (AIS). Androgen resistance and androgen insensitivity (developing embryo fails to respond properly to male hormones)
May be partial (PAIS) or complete (CAIS). No female internal structures, but male structures fail to form properly. Failure of masculinization ranges from mild (some masculinization occurs), to complete (no masculinization occurs).
Testicular Feminization Syndromes (Tfm) XY. Androgen receptor gene mutation. Normal embryo testosterone levels, but target organs fail to respond appropriately. Ranges from complete to partial failure of androgen-dependent masculinization. When the androgen receptor is completely nonfunctional, males appear entirely female, but sterile and do not have oestrus. Internal female structures absent. Complete Tfm.
When the androgen receptor has partial function (incomplete Tfm) it gives ambiguous genitalia through to phenotypic males that are infertile.. Domestic shorthaired cat (1989). Bilateral abdominal testes were present, but no epididymides, vasa deferentia, or uterus. External genitalia were female.
Incomplete Tfm may occur in cats, but has not been well documented
Hypospadias Associated with XX Sex Reversal and other conditions giving ambiguous genitalia. Urethra located on underside of penis due to incomplete masculinization. Ranges from mild through to urethra exiting near base of penis.
Cyptorchidism & Monorchidism May occur as separate from conditions listed previously and cause not known. May be genetic, may be developmental.
Delayed descent may be a variant of cryptorchidism. Undescended testes. May be unilateral (monorchid, may be fertile) or bilateral (crytporchid, sterile). Yes. Affected monorchid cats should not be used for breeding as trait may be hereditary.
Delayed descent noted in some male cats.


SUMMARY: MANY FORMS OF MOSAICISM
Mosaicism (the visual effect of a multicoloured coat) can take many forms, from normal female tortoiseshells, through to individuals that are actually two fused individuals. The visible effect may be due to somatic mosaics, chimaerism or X chromosome inactivation. In females, mosaicism is normal. In males it is associated with genetic or developmental abnormalities. Other forms of mosaicism and chimaerism do not have a visible effect but may affect the genes passed on to offspring; in germ-line mosaics this leads to "genetically impossible kittens".
BRODY BAKER - male tortoiseshell Klinefelter giant, Dublin, Ohio, USA (by Laura K Baker)
Brody is my 7 year old Klinefelter Syndrome cat who has male anatomy and the signature tri-color calico pattern found nearly always in females. After starting life as a very scrawny "runt," he has blossomed into a giant cat with a heart of gold and a passion for cheese!
My husband and I adopted Brody as a kitten from our local veterinary hospital, where he was scheduled to be euthanized that week. A few days earlier, a man tried to drop some kittens off at the adjacent pet store and ended up "tossing" Brody and his calico sister into a window after the store clerk told him they didn't accept cats off the street. The other calico was fine and put on sale. But because of his genetic defects, Brody's hip bone snapped when he was thrown into the window. Apparently he was born with a cyst in the bone. Because of that - and his other obvious genetic defects - misshapen back feet, front toes turned outward - Brody was scheduled to be put to sleep that week.
Timing is everything. I noticed the little calico asleep in a cage at the vet where I was visiting my other cat, Max, who was getting neutered. I asked the vet why the kitten was all alone in an isolated cage and she told me the whole sad story. I said, "Don't do anything with that cat. I want him."



The vet explained his condition -- that he was a rare, but likely very weak, Klinefelter Syndrome cat, who probably wouldn't live very long. She didn't do any special medical testing to reach this conclusion, but had learned about the condition at vet school. Between his distinct calico markings, unmistakable male anatomy, shattered hip and misshapen feet and legs, the vet figured this XXY cat was not long for this world.
I didn't care - I wanted to give this tiny kitten the best life I could for as long as I could. So the vet volunteered the hospital stay and medical care to repair his shattered hip bone. My husband and I paid only for the raw materials. Six weeks later - after one operation and several casts - I took Brody home. He has been healthy as a horse ever since. He still walks with a very noticeable limp - and his feet and toes remain misshapen - but he can run and jump and he isn't in any pain. For a scrawny kitten who wasn't given very good odds at first, he has thrived.



He started gaining serious weight around age 2. Initially we tried a lot of different techniques to help him lose the weight. I even started taking him outside for "walks." Despite all that, he continued to gain weight at a rapid pace. Various vets said he seemed to be healthy despite the extra pounds. Now, at age 7, I realize and accept this is just his unique body shape and as long as he is healthy and happy, I'm OK with that. At last weigh-in he was 25 pounds. I don't know if this is a trait of all XXY cats, but I have heard that it can be -- and I wanted to share this story and pictures. He's a light in our lives and we love him unconditionally -- not because he's rare or special -- but because he's Brody - a kind-hearted soul who just happens to have an extra chromosome.
CATS OF MANY COLOURS!
The distribution of orange and black in a normal tortoiseshell cat depends on the migration rate of the cells and on the randomness of X chromosome inactivation. The photos below show a selection of different tortoiseshell cats. Other variations of tortoiseshell and calico cats can be seen in Tortoiseshell and Tricolour Cats.

_________________
Обсуждаете мою жизнь? Значит она интереснее вашей!
Плюете мне в спину? Значит я - впереди!


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