Animal World - cat genetics: sex linked heredity and sex limited expression

Image: Table Top

ex-inked eredity

The gene B responsible for the black coat has his locus on the ordinairy chromosomes.

The O gene responsible for the red coat of cats is located on the X-chromosome. In fact there are 2 genes: O for red, and o for not-red.

Just like the chromosomes, genes always make pairs, except the genes located at the X-chromosomes. They can not always make pairs because males only have one X-chromosome. Males can have an O gene (being a red cat) or an o gene (being a black cat).

Females can have 3 possible combinations:

tortoiseshell Persian * two O genes (OO) being a red cat;
* two o genes (oo) being a black cat;
* one O gene, with a o gene (Oo).

This will result in a cat being a red cat and a black cat at the same time (tortoiseshell).

Image: Table Top

|| Charlie || Princess || Disney || kittens || spay & neuter || pictures || Rainbow's Bridge ||
|| the Persian breed || history of the Persian breed || sense organs || body || behavior ||
|| chromosomes || genes || interaction between genes || heredity & the sex ||
|| screen friends || animations || funny pictures || did you know... || links ||
|| home || ©, privacy, etc. || site map || e-mail || guestbook || CSS || XHTML ||

Image: Table Top

This is the reason why a tortoiseshell is always a female. There are cases where a tortoiseshell male was born, but this is a disorder of nature: male-cats with 3 sex chromosomes (XXY); in most cases they are sterile.

There are more genes responsible for the coat of cats, for instance:

* the A gene (agouti) for tabbys;
* the d gene (dilution) for the diluted colors like blue or cream.

For all those cats you can use the basic of sex-linked heredity.

!!! An example of human sex-linked heredity is colorblindness. Colorblindness is caused by a recessive gen located on the X-chromosome. The majority of people suffering from colorblindness are male because they only have one X-chromosome !!!

ex-imited xpression

wise cat There are cats nursing their kittens that have a lot of milk and other cats don't, so you have to help her feeding the little kittens. The fact that a cat produces a lot of milk doesn't necessarily mean that she inherited this from her mother; maybe her father is responsible for the great milk production.

Males and females both carry the same genes for this quality. A male cannot show this quality, because he doesn't produce milk, but the genes are there !!!

Another example of sex-limited expression are the monorchide and cryptorchide males. Monorchide males have only one testicle, and cryptorchide males don't have any testicles.

The defect is due to a recessive gene. When there are monorchide or cryptorchide kittens in a litter often the stud gets all the blame, but the fact that a kitten is monorchide or cryptorchide, means that it has two genes responsible for this defect, and both parents are to blame!!! Some breeders make the mistake of using another combination and then the problem seems to be solved, but that is not true.

Even if there are no monorchide or cryptorchide kittens in future litters when using another combination, the mother will pass the recessive gene on to at least 50% of her kittens. In the worst case she is giving the recessive gene to all of her kittens, without any of the kittens showing the defect. The only correct solution is to eliminate both parents from your breeding program.

cat at vet