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The intrigue of cat genetics; a primer (part 1)


Oct 13, 2016
i am a biologist. Genetics have to do with statistics so even though a litter may have a 25% or 1 in four chance of having a trait, it may ne that 100% of the kittens exhibit the trait or it may be that none of the do. Over a very large number of litters, the statistics will be accurate.

Genotype is what the cat is genetically. Dominate traits are capitalized and are alway written first no matter whether the trait came from the male parent or the female parent. In the case of the Sphynx, hairlessness is recessive. Recessive genetic traits are denoted by small letters The sphynx hairless genotype is hrhr.

Phenotype the cat exhibits. The phenotype of the offspring of a haired cat(that doesn't carry a hairless gene) and sphynx, will always a haired cat that carries a hairless gene.

Phenotype, without further genotype information is written with the trait and a blank. In the case of the haired kittens above, the phenotype would be written; H_

The genetic information that we have for the outcross example above of the haired cat(HH) and sphynx(hrhr) lets us know that all kittens from that outcross will be genetically Hhr, i.e. They are haired cats that each carry the hairless trait.

This is where it gets interesting. Let's breed our haired outcross offspring Hhr to a sphynx hrhr. Since each parent can only contribute one gene to our theoretical kittens we know that our Hhr (haired offspring) can contribute either an H or hr but not both, each theoretical kitten has a 50% chance or 1 in 2 chance of receiving the hr gene. Our sphynx can only contribute hr because the sphynx only has the hr gene. In the cross we will get 1/2 of the kittens that are haired and 1/2 of the kittens that are hairless. All of the kittens will carry the hairless gene but only 1/2 of the kittens will show it.

Now let's breed two haired cats that carry the sphynx hairless gene to each other. Each parent is phenotype, haired H_, but genotype Hhr. The resulting kittens will be 1/4 of the kittens HH, haired no recessive hr gene, 1/2 of the kittens Hhr, phenotypically haired but carrying the hairless gene, and 1/4 of the kittens hrhr, hairless. The only kitten that we can be sure of their genotype is the hairless kitten because if the kitten carried the haired gene (H) the kitten would be haired.

So how do we determine which of our haired kittens from the outcross Hhr, Hhr, carry the hairless gene? There are two ways. The first is by having the kittens' genotyped in the laboratory. The second way is to breed the haired kittens to a sphynx. If there are any hairless kittens in the litter, we know that the haired parent carries the hairless gene. But the converse is not true; i.e. If all the litters have only haired offspring, that doesn't guarantee that that the parent doesn't carry the recessive hairless gene.