Genetics Simplified: Cats

If you've gone through a biology course or mixed stem course, you are probably aware of the topic inheritance. If you are not, or you need a refresher, the following will be a quick overview! Every animal has DNA, or biological genetic code. Through the course of reproduction, the formed individual will get alleles, or a specific version of each gene that has multiple variations. These will come from both of their parents, and the individual will inherit these traits. These alleles form the DNA which form chromosomes, which are essentially genetic code packages in the form of hundreds or thousands of genes. Together, the chromosomes make up an entire animal.

The way the gene then represents itself in an animal is the phenotype. Another way to think about phenotypes is that they are what the gene physically appears as. Behind the phenotype is a genotype, in which each allele is represented by either a capital letter or a lowercase letter. The uppercase letter means that the allele is the dominant version, and if an animal even has one of these dominant alleles, their phenotype will appear as the dominant phenotype. Lowercase letters are recessive versions of alleles, and an animal has to have two of the recessive allele for the recessive phenotype to appear. A complex example of this is the color of human eyes, which is comprised of several genes that control pigment. Blue is the recessive color in human eyes.

There are many other gene controlled traits in humans, but a much simpler example to look at is the common house cat. Domestic cats have 38 chromosomes, or 19 pairs of chromosomes. Humans have 46, or 23 pairs, and domestic dogs have 78, or 36 pairs!

So, what are some common genes in cats that we can talk about? Well, the most prominent thing we first notice is most likely the fur color. Cats have a wide variety of different fur patterns and colors, each of which is controlled by some genes.

Before we continue, we should talk about Punnett squares. Punnett squares are a way to look at the inheritance of alleles by using the parent alleles to form a table of probabilities.

Just by looking at the above punnett square, we can see that there is a 50% chance the offspring will have the 'Bb' genotype, and a 50% chance the offspring will have a 'bb' genotype. Having both alleles be recessive or dominant is referred to as homozygous, meaning the alleles are both the same. If one allele is dominant and the other is recessive, it is referred to as heterozygous, meaning the alleles are different.

What would this mean for a cat? In cats, the B and b alleles refer to two different fur colors: capital B refers to black, while lowercase b refers to chocolate. There is a third b gene in cats, which is b' (b prime), which would represent cinnamon. B is the dominant allele, with b being recessive to B, and b' being recessive to both B and b.

However, you probably know a cat like Garfield, with bright orange fur! This isn't on the same gene as the black, chocolate, or cinnamon traits. Instead, this gene is called the red gene (represented by the letters O and o), and it is found on the X chromosome.

The X chromosome is a sex determinant gene that is also found in humans. Individuals with two X chromosomes are biologically female, just as they are in cats. An individual with 1 X chromosome and 1 Y chromosome is biologically male. Any gene found on a sex determinant chromosome is referred to as sex-linked.

What would that mean for cats? It means that individuals with only 1 X gene- those that are biologically male- are far more likely to be red or orange in coloration. In fact, it is about 4 times more likely for an orange cat to be a male! Female cats can also be orange if both X chromosomes carry the red gene. However, female cats can also have one copy of the red gene on an X chromosome and have it absent on the other X chromosome. This results in a color pattern referred to as tortoiseshell; this is a combination of orange and any of the letter B allele colors. This means that the tortoiseshell pattern is genetically impossible in males; the only way a male could be a tortoiseshell is to have the XXY chromosome pattern, which would result in him being sterile, or unable to reproduce.

What about white cats? White is a color in cats that is more complicated than the above. There is a white spotting gene that means that cats can have areas of white almost anywhere, including being up to 100% white, but there is also a white dominant gene that causes a cat to be fully white. The dominant white gene is represented by the letter W (DW). A cat with just one W (or DW) will be fully white, while a cat without it (w) will not show any sign of white dominance. The white spotting gene is represented by the letter S (ws), and it can be anywhere from 0% to 100% white. The white spotting gene coexists with other genes, meaning that the cat will show its other genetic colors in non-white areas (unless it is fully white). There is also a third gene referred to as white gloving which gives a cat white paws (wg). All three of these genes can interact and cause for different white patterns to appear, and are listed in order of gene dominance.

How can you tell the difference between a cat with 100% white spotting and one with white dominance? The answer is all in the eyes of the beholder: a white dominant cat will have very pale blue or amber eyes (orange), while a white spotting cat will have green or yellow eyes. A white dominant cat is also incredibly likely to have hearing impairment or be totally deaf.

Note: the white genes are not the same genes responsible for albinism.

The white spotting gene also causes some of the most adorable cat patterns. Tortoiseshell cats with white patches are called calico cats. Cats with enough white to look like they are wearing a little fur suit are called tuxedo cats.

Cats can also have diluted fur colors, represented by a capital D for diluted and lowercase d for non diluted. Diluted black is gray (also called blue), diluted chocolate is lilac, diluted cinnamon is fawn, and diluted orange is cream.

The last cat genetic markings that we will talk about are tabbies. The cat that was yawning at the beginning of this story was a tabby cat. A tabby cat is a cat with stripes or spotted markings traditionally, but some tabbies have swirled or even ticked markings.

The agouti gene is the gene responsible for tabby cats. A capital 'A' means that the cat will have agouti markings, while a lowercase 'a' means that the agouti markings will not be present and the cat's coat will be solid in color. a non-agouti cat can carry any tabby pattern, but it won't be physically displayed. However, the type of tabby depends on variants of the tabby genes present.

The most dominant gene in tabby markings is the ticked tabby. Ti-+ (ta) represents the recessive not ticked allele, while Ti-A (TA) represents the dominant ticked allele. The next step in dominance goes to the mackerel (striped) tabby, which is represented by Ta-M (Mc); the recessive variant of this gene is ta-b (mc), which causes classic (swirled/blotched) tabbies. Finally, there is the spotted gene- the most recessive tabby variant we will be discussing. It is represented by Sp, meaning that spotting is present, and sp, meaning that no spotting is present. A ticked cat could be carrying mackerel, classic, or spotted markings, but these will not display physically; the same applies as you go down the dominance list.

There is one exception to the above, and that is found within red/orange cats. All orange cats will appear to be tabbies. Essentially, the non-agouti gene will not repress the red gene. Some red cats may appear to be solid orange, but upon closer inspection, they will have faint tabby markings regardless. A non-agouti red cat is called a 'false tabby' or a 'ghost tabby' as a result of this.

You've just learned a whole lot about how cat coloration works biologically. Congratulations!

If you simply love cats, or just love animals in general, consider donating to Trap/Neuter/Return programs. Every year a single female cat can have 12 kittens in the wild if she has not been spayed, and while cats of all colors and genotypes are equally adorable, this can cause havoc upon local small wildlife- anything from birds to squirrels and rabbits can have their entire populations wiped out, and several species (about 63-70 in total) have already gone extinct this way!

Many of these feral cats simply could not acclimate to life within the home, and are much happier in their home colony. That is why spaying and neutering them and then re-releasing them is so important.

Consider going to the following links to donate and learn more:

Thank you so much for reading and learning alongside me.