When you breed a carrier to a carrier your chances are: 25% ataxia, 50% carrier and 25% free
When you breed a carrier to a non carrier: 50% carrier and 50% free
When you breed two free cats together, you have: 100% free
Also, when you breed now, i.e. 5 generations away from a carrier, this cat has only two chances: It can be free or it can be a carrier. It can not be a 12.5% free cat or a 6.25% carrier cat or something else like this.
If this cat is still a carrier and you breed it to a non carrier, you have again: 50% carrier and 50% free
And if you breed it to a carrier, you have: 25% ataxia, 50% carrier and 25% free
Try to compare this with the dilute gene. A cat with dilution very far in its pedigree, has also only the chances to carry dilution or not. 50% to 50%. Not 87,5% to 12.5%. It is like a switching position on the gene locus of this non diluted cat: You have only the two positions “dilute carrier” or “dilute gene off”. But you never have a cat with 12,5% dilution, also when it would be funny to have a black cat with a blue tail?
For example, Barbara Azan states: This simile will explain how the genetics works during the conception of each individual kitten.
Take a sack full of beans, black beans representing the carrier cats and white beans representing the free cats. For each kitten take two beans out of this sack without looking. If you get two black beans, you have an ataxic kitten; if you get the combination black x white, you have a carrier; and when you get two white beans you have a free kitten. You take away the black beans out of the combination black x black by neutering the known carriers, then put all the other beans back in the sack and you start from the beginning. You will find that you will come to the point, when the possibility of black x black is VERY low (as are the chances of ataxic cats), but it also means there are still black beans in this sack, which are more easily hidden under all the white beans.
If this example is not exactly the accurate in all points, as the ataxic problem, it still makes clear, that the chances of picking out the last two black beans together out a sack with 100 white beans is almost impossible. But what you will never take out of this sack are grey beans or 12.5% black/white beans.
Authored by:
Ute Kunze, Hosca Kal Turkish Angoras
Barbara Azan, Azima Turkish Angoras
