So many times, the question is asked – if I breed a cat of x color to a cat of y color, what color will the babies be?
Usually, people who understand color genetics will just list out the possible colors. It’s often easier to do that, rather than actually explaining about colors and genetics.
The purpose of this article is to explain color genetics in the most basic form possible, starting with the smallest part and building from there. This is to help people learn how to determine the possible colors for their litters without having to resort to asking others every single time. Also, if a breeder isn’t too sure of genetics and wants to breed for certain color(s), this should help plan out breedings.
The Absolute Basic Idea of Color Genetics
When you take away all the fancy modifications, additions, dilutions, etc of cat genetics, you will discover that really, there are only 2 genes for color. That’s right – 2 – nothing more and certainly nothing less.
What are those 2 colors? Black or Red (also sometimes called Orange).
Now a little of cellular structure must be understood to expand to the next point. Inside of every cell in every living creature, from the simplest bacteria to humans, there is a substance called DNA. DNA is basically the blueprint by which all parts and bits of an organism is made. The DNA for every organism is different – just as each human has unique fingerprints. However, there are also parts of the DNA “blueprint” that are shared (just as all humans have hands and fingers, even if the fingerprints are different.)
DNA is incredibly long and complex, and it is broken into smaller pieces within the cells of animals in order to be more functional. Those pieces are called “Chromosomes.” Because DNA is the most absolutely complex and incredible instrument of the living world, it has a built-in redundancy system – that is, a copy – that it keeps with it all times. To put it in simple terms, there are two copies of the DNA in each cell. Each copy is virtually the same, though small parts might have differences (such as the size of your ring fingers might be the same, but the prints are still different). There is only one exception to this rule, and that is the pairing of the “sex” chromosomes. That pairing is either XX (named because they appear to both be in X shapes) for females of XY for males. (Fun Fact: The “Y” chromosome is actually a “wilted” or degenerate X. So every male animal is actually half a female. <gr>)
Each parent donates one copy of their DNA to the offspring, and that explains why the two copies can have different genes. Since females ONLY have X chromosomes, they can only pass on X chromosomes. The males can either pass on X or Y, so it is the father that determines the sex of the offspring. There are other chromosomes other than X and Y, but they are identical in both male and female.
Now we can come back to the Black and Red concept. Genes for different things, such as hair length or eye color, are found on the chromosomes that are NOT the sex chromosomes. However, the location of the gene for black or red is on the X chromosome. Since male cats only have one copy of the X chromosome, they can either be black or red – but not both. Females, on the other hand, can have two copies of black, two copies of red OR one copy of each – which is the foundation for what one might call the "3rd Basic color" – Tortoiseshell.
Moving On – A little genetics vocabulary
If you have spent anytime with genetics, you will have heard the terms “Dominant” and “Recessive,” though they might not have meant anything to you.
Remember that DNA has two copies of each gene within the cell. Sometimes, both copies of the gene are exactly the same. However, when they are not, often times one gene is capable of suppressing the other and stopping it from “working.” A gene that suppresses another gene is called a “Dominant” gene. A gene that is suppressed is called “Recessive.” In order for a recessive gene to be “seen,” it must be present on both copies of the DNA (that is, all recessive, no dominant gene present)
In the case of Black and Red, it happens that they are both Dominant, so in female cats, you see something called “co-dominance” when they have a copy of each gene (some of the cat is black, some of the cat is red.)
Another pair of terms that are linked together are “Homozygous” and “Heterozygous.” Remember that sometimes the two copies of the gene are exactly the same? That is what “homozygous” means – both copies of the gene are the same. Heterozygous means that the two copies are different.
There are many other terms that go with genetics; however, they are not necessary to understand the rest of this article.
Now, let's take a look at how you can get from black, red, or tortoiseshell to all the varied colors we see in Persian cats. This can be most simply explained by “modifier genes.”
There are genes on other chromosomes – not the X or Y-chromosomes – that can change or modify the black or red color. I have put those genes into categories:
- Pointed (Himalayan)
Remember, none of these genes are located on the X or Y-chromosomes, so they are not linked to the sex (gender) of the cat. So males and females both have two copies of each “modifying” color gene.
The dilute gene is a recessive gene. So, if at the “dilute” loci, there is a copy of the “dilute” gene on both copies of the DNA, a black cat becomes blue, a red cat becomes cream, and a tortoiseshell becomes a blue-cream.
If there is only ONE copy of the dilute gene, the color of the cat DOES NOT CHANGE, but the cat can be called a “dilute carrier,” and that cat can produce dilute offspring IF bred to another dilute cat or dilute carrier. If 2 dilutes are bred together, ALL the offspring must be dilute as well.
The pointed (or Himalayan) gene is also recessive, so a cat must have 2 copies of this gene in order to be pointed. Two copies of the pointed gene will make a black cat become a seal point, a red cat will become a flame point, and a tortoiseshell becomes a tortie point. If a pointed cat is bred to another pointed cat, all the offspring will be pointed.
It is important to note that some breeders – most, in fact – use the distinction of “pure” Persian for Persians that have NO pointed cats in their background. Persians with pointed cats in their pedigrees are called “CPCs,” which is short for “color-point carrier.” Color point is another term for “pointed” or “Himalayan.” However, this term is a little misleading, as not ALL cats that are “CPCs” are actually carriers of the pointed gene. For a more in-depth discussion, please read What is a CPC?
Chocolate is a very special gene that can only modify the Black gene. It has no effect on the red gene. It is also a recessive gene; so again, it must be present on both copies of the DNA in order to be visible. Two copies of the chocolate gene will make a black cat become a chocolate, a red cat will not change color – it will still be red – and a tortoiseshell cat becomes a chocolate tortie (the black parts are now chocolate, but the red is not changed).
Cats with two copies of the chocolate gene are often called “Visual chocolates,” which is often shortened to “Visual” since the chocolate can be seen with the eyes, rather than being hidden in the DNA. Since the chocolate gene originated from the original Siamese crosses with the Persian to open up the gene pool for the Himalayans, ALL chocolates and chocolate carriers will be labeled as “CPCs.” The chocolate gene, when it interacts with the dilute gene, creates “Lilac.” It is important to note that a red cat can have two copies of the chocolate gene – these cats are referred to as “Red chocolates.” That simply means that all their offspring will carry the chocolate gene, or show it if they are bred to another chocolate carrier or visual chocolate.
Tabby is a dominant gene, so a cat only needs one copy of this gene in order to “show” tabby. With the tabby gene, a black cat becomes a brown tabby, a red cat becomes a red tabby, and a tortie becomes a brown patched tabby.
If a cat has two copies of the Tabby gene (homozygous tabby), then ALL offspring will have at least one copy of the Tabby gene, therefore, all offspring will be tabbies of some sort.
Bicolor is also a dominant gene, so again, only one copy of this gene is needed in order to be visible. With the bicolor gene, a black cat becomes black & white, a red cat becomes red & white, and a tortoiseshell becomes a calico.
If the cat has two copies of the bicolor gene, often the cat is mostly white, otherwise known as a “Van Bicolor.” These cats will always have all bicolor offspring, no matter what they are bred to.
Smoke is a dominant gene, so it cannot be "carried" in the DNA or hidden from sight - unless masked by White. One copy of the smoke gene will turn a black cat into a black smoke, a red cat into a red smoke, and tortoiseshell into a tortie-smoke. A cat with two copies of the smoke gene will always produce smoke offspring.
The smoke gene is one that can cause some confusion due to a concept called "variable penetrance." Basically, that means that some cats with the smoke gene have a mostly colored hair shaft with a white undercoat. Some of them will be about 50/50 on the hair shaft in respect to color/white. These cats are called "shaded." Finally, some cats will have a mostly white hair shaft with color just on the tip - these are called "shell," and they tend to be very rare. Some of these colors are not recognized by CFA - black smoke is, but black shaded and shell black are not, while oddly enough, the tortoiseshell is recognized as smoke, shaded and shell.
Additionally, when a red cat is "shaded" or "shell" it is called a "cameo" or "shell cameo." The dilute version of this, cream shaded or cream shell, is called "cream cameo" and "cream shell cameo." Some effort has been made to remove the term "cameo" as it is rather confusing to those who are not very familiar with smokes. I am not going to get into the whole genetics of smokes/shadeds/shells - this is simply an overview. A whole book could probably be written on them!
Of all the colors or divisions of Persians, the Silver and Golden is probably the least understood by those who do not work with these colors – and perhaps even by those who do! These unique and beautiful colors are a combination of genes working together to produce an overall effect. The first gene is actually the “Tabby” gene, which is often called “agouti.” The 2nd gene is called the “inhibitor” gene, which is actually the same gene as the smoke gene. The final gene, or set of genes, actually, is what sets the silvers and goldens apart and makes them so unique. These are termed “wide banded polygenes.”
All three of these genes are dominant, so they cannot be carried or hidden unless the cat also has a copy of the White gene. As with the chocolate gene, the polygenes do not have any effect on the red color (other than eye color, and this isn't quite understood, so I will not get into that). The polygene can have “variable penetrance” just as the smoke gene can, which is what causes the range of silver colors from shaded silver (which has a fairly heavy layer of black, easily seen) to the chinchilla silvers (which have just a dusting of black, they appear to be a white cat with just a dusting of color.) It can be argued that a shaded black and a shaded silver are the same color: however, they are not. The shaded silver will have green eyes and eye/nose liner, and it will overall be a lighter called cat. It follows that a shell black is not the same as a chinchilla for the same reason (this is because the shaded shiver and chinchilla silver have two dominant genes NOT found in the black shaded or shell black – the Tabby gene and the “polygene.”)
A golden is produced by a cat that has a Tabby gene and the polygene, but no inhibitor (or smoke) gene. I am not going to delve any further into the silver/golden genetics, as with the smokes, that would take a whole article all on its own. The best article I found when researching this was this one: Silver And Golden Genetics. I highly recommend it if you would like to know more about the genetics of silvers and goldens.
I have placed white alone because it is a very special category unto itself. In a way, in the world of Dominant genes, the white gene is the ultimate king of the hill. It trumps all other genes for color, no matter if they are dominant or recessive.
So with the white gene, the black, red, and tortoiseshell cats all become the same color – white. If a cat has one copy of the white gene, it will be white, and about 50% of its offspring, when bred to non-whites, will be white. A cat that has two copies of the white gene is referred to as a “homozygous white” and 100% of its offspring will be white – regardless of what color it is bred to.
The white is a “masking” gene, meaning a cat can have a color in its DNA, but that color is suppressed (the same way a normal dominant gene suppresses a recessive.) Sometimes, people comment that white isn’t really a color of cat, since it’s really just the result of the suppression of color. (I am not going to delve into an explanation of odd and blue eyed whites in this article.)
In Part 2 of this article, we will take a look at how to look at a cat's color, and "construct" or "deconstruct" the modifying genes that create that color, as well as look at how to answer the question of "What color kittens will I get".
About The Author:
Carissa Altschul has been involved in raising and showing Persians her whole life, in a literal sense! She was born in 1978, and her parents had already been raising and showing Persians (Himalayans, actually) for 7 years before she was born. Her earliest memories include many of sitting in a portable baby crib in a show hall and watching her mother, Janet, groom the cats for the rings.
Carissa took an active interest in showing cats in her early teens, attending shows with her mother for many weekends out of the year. As the years went by, Carissa started going to the shows by herself, loving the experiences, and Janet decided she was happier staying home for most of the weekends.
Attending as many as 24 shows a year, Carissa has a busy schedule with her showing, not to mention the time at home to take care of the cats there. Carissa is also an active member of the CFA Mentor program, for she has found that helping new people was something she loved to do even before the program started. In the future, Carissa is considering joining the CFA Judging program, but she has no immediate plans to start that any time soon.