Genetics 101

Banner Photo Credit: Cutepawsmeow

Well, probably we should have started our blog with this post. As they say, better late than never ;)

So we are going to talk about basic genetics today. The feline genome was fully decoded in 2007. Of all of the cats in the world, a 4-year old Abyssinian cat named Cinnamon was chosen to be a genetic model for all felines in a project called the feline genome project. By donating a small vial of blood, Cinnamon provided scientists the wherewithal to map the feline genetic structure, eventually allowing for each gene's function to be noted and studied.

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Genetic data is important not only for breeders that try to introduce special coat color to their line, but also to the regular cat owners. Why? When you understand the origins of your cat, you can more easily predict the health and behavioral issues. You can choose better food and provide better care based not only on your cat’s taste, but also on the unbiased data. Most importantly -- your cat can’t talk, but their DNA can tell you more about them than anything else on the planet.

Some basic vocabulary

Unlike people, cats have 38 chromosomes that come in 19 matched pairs (aka "autosome genes", unless it is a the sex-determining X or Y). Each pair is called alleles of genes, but we will be using "genes" for simplicity. One gene in each pair is inherited from each parent and the pair carries information a trait or a group of traits such as long or short fur. As Leslie A. Lyons (she is the Queen of feline genetics) points out, "Approximately thirty-five genes contain over fifty mutations that cause feline health problems or alterations in the cat’s appearance".

DNA in chromosomes

Dominant genes are the ones that appear among the kitten’s physical characteristics when he is born. To have the trait the kitty needs only one copy of the dominant gene. Recessive genes are carried in his genetic code and can influence his offspring. They are expressed only if two copies are inherited. An animal where both copies of the gene are the same is homozygous for that trait. An animal where the copies are different is heterozygous for that trait.

According to convention, a dominant gene is shown in uppercase and a recessive gene is shown as the same letter, but in lowercase. In some cases, neither gene is dominant. The genotype Xx would then give a phenotype (appearance) intermediate between XX and xx in the same way that pink is intermediate between red and white.

But not so simple. Most traits are inherited separately from each other because the genes occupy different loci (plural of locus) on the chromosomes. But some traits are inherited together because the genes are located close to each other and tend to be passed along together. Think of this as a shared balcony between apartments on 17th floor of a building.

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Enough with the "back to biology" lesson, let’s talk about fun stuff!

Interesting fact #1. Cats and humans share about 250 genetic diseases.

Cinnamon's pedigree carries a genetic mutation that causes retinitis pigmentosa (PRA), a degenerative eye disease that can lead to blindness in humans by the age of 40. While Cinnamon was not blind at the time of the research, she did have vision problems.

"Which means that the visual cells, the rods and the cones, die and this disease is very similar to human retinitis pigmentosa, which is a blinding disease that affects one in 3,500 people worldwide," said Dr. Narfstrom, who lead the feline genome decoding. Cinnamon and other cats in the colony became the ideal test subjects for the microchips as one of the way to find a cure for this disorder.

Photo credit: bizzibabs_pra_siamese

In cats, PRA can be either inherited or acquired. Bizzi, a Basepaws family member from South Africa is not a carrier (his pet human Lindsay did the DNA tests!). He came to this world as a sighted kitten and by his 2nd birthday he was totally blind and this is why all his family is involved with PRA Awareness: "Kittens with PRA, sadly, will be blind before the age of 5 years. Our aim is to share this fact with everyone and hopefully breeders will start testing their cats before breeding with them."

Interesting fact #2. White fur color! White is a dominant gene.

When present, dominant white masks out any other color genes. The cat has a white phenotype but also has the genes for other colors and passes on those color genes to its offspring.

This happens because the W gene resides at a different place (locus) the chromosome or on a completely different chromosome and hence masks the effect of certain other genes. Sometimes it is called an "epistatic white". Another "epistatic" gene is the orange (O) gene. He is linked to the X gene - this is called sex-linked. It masks the effect of the black gene by converting a black or brown coat to orange.

Interesting fact #3. Both genes can be dominant.

What happens if two dominant genes are met? Which of the two "wins"? The gene for a given trait is not always dominant or recessive; there can be more than two alleles for some traits, that is, there may be more than two possible phenotypic expressions. For instance, the gene for "eye color" is not just "brown" or "blue;" there are green eyes, and hazel eyes, and grey eyes, and so on.

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In any given pairing of different alleles of the gene for eye color, one will be dominant over the other. If both genes of a pair are the same recessive allele, then of course that is what gets expressed, as well. Each gene carries either "the" dominant, or "a" recessive, version of that trait. Another example is the gene that encodes your blood type (the ABO gene). There are at least three alleles of the gene - A, B, and O. A and B are both dominant to O. However, they are codominant to each other. When you look at a red blood cell of someone with an AB genotype, you will see both A and B antigens.

Now let’s play a game! Crack this case and get a chance to win wants a free DNA kit!

Two black cats can produce a white kitten! Or not?

Let’s say that black is a dominant trait, and white is a recessive trait. If we call the allelle, responsible for this pigment "gene A", the black version of the gene would be "A" and the recessive version - "a".

So how can two black cats have a white kitten? Post the answer in comments for this blog post on our Facebook page and we will randomly select a winner.

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