It’s not uncommon for a litter of kittens from the same parents to have different coat colors and patterns. This is due to the complex genetics that determine feline coat characteristics. Cat coats are governed by several gene pairs that interact to produce varying phenotypes. The genes responsible for coat color and pattern are incompletely dominant, meaning a kitten can express a blend of traits from its parents. Additionally, random mutations can introduce new variations. Understanding the genetic basis for cat coat diversity can help explain why kittens from the same litter can look so different.
Genetics of cat coat color
There are two main genes that control the basic coat color in cats:
| Gene | Alleles |
|---|---|
| B (Brown) | B – Black pigment b – Lack of black pigment (allows red/orange to show through) |
| O (Orange) | O – Allows red/orange pigment o – Blocks red/orange pigment |
Cats with BB or Bb will produce black pigment. Only cats with bb will produce red/orange pigment. The O gene controls whether red/orange pigment can be expressed. OO or Oo allows expression of red/orange. oo blocks red/orange even if the cat has bb.
Some examples:
| Genotype | Phenotype |
|---|---|
| BBOO | Black |
| BBOO | Black |
| BBoo | Black |
| BboO | Black smoke |
| bbOO | Red/orange |
| bboo | Brown tabby |
As you can see, a cat’s basic coat color depends on the combination of alleles inherited from its parents. Other genes modify this base color to add patterns, shading, points, etc.
Coat patterns
Several other genes control the patterning of fur on cats. These include:
| Gene | Effect |
|---|---|
| A (Agouti) | Coding for tabby patterns |
| T (Ticking) | Banding on hairs instead of solid color |
| S (Spotting) | White spotting and piebald patterns |
| W (Dominant white) | Extensive white coloring |
The agouti gene produces the classic tabby patterns of stripes, swirls, blotches, etc. Ticking adds bands of color on individual hairs. The spotting gene S controls the white areas in spotted tabby, tuxedo, van, and calico patterns. Dominant white W masks most other colors and produces solid white cats.
Again, kittens can inherit different versions of these genes, resulting in an array of patterns. For example, one kitten may get tabby Agouti from the mother and piebald spotting S from the father. Another may get non-agouti from both parents and have a solid coat.
Random mutations
In addition to inheriting varied combinations of coat genes, kittens can also exhibit new traits not seen in the parents. These arise from random mutations in the genes governing color and pattern. A kitten might receive a mutated allele that inhibits production of red pigment, turning a calico into a tortoiseshell. Or a mutation could activate a gene for pointed coloration. While uncommon, novel mutations help explain why some litters exhibit coat colors unlike either parent.
Coat colors and cat breeding
Understanding feline coat genetics has allowed cat breeders to propagate desired colors and patterns. Breeders select parent cats that are homozygous for traits they wish to perpetuate. If both parents possess the alleles for that characteristic, all offspring will exhibit it. Examples include producing guaranteed tabby Scottish Fold kittens or blue point Siamese cats.
However, heterogeneity can also be desirable. Crossing cats with different traits, such as a mackerel tabby and a tuxedo, will generate kittens with an assortment of patterns. Multi-colored litters are prized in breeds like tortoiseshell Persians and calico Japanese Bobtails. Controlled outcrossing maintains genetic diversity and allows expression of the breed’s full spectrum of coat colors.
Sex-linked coat colors
Some coat colors are sex-linked and depend on whether the cat is male or female. The classic example is the orange gene. Males only need one copy of Orange O to exhibit red/orange coloring. But females require two copies of O. Otherwise, the phenotype is a tortoiseshell or calico pattern of patched orange and black. Thus, male calicoes are extremely rare. Other sex-linked colors include cream, chocolate, cinnamon, and some types of pointed pattern.
Coat color changes as cats mature
Kittens are often born with a “placeholder” coat color that changes as they mature. Newborn kittens have a protective layer of longer, thicker fur before growing their permanent adult coats. Solid black kittens frequently develop tabby stripes or smoke patterns later in life as the juvenile coat sheds. Pointed kittens lack markings at birth then develop their signature color points as adults. Even orange kittens may be pale cream before reddening with age. Noting coat color at birth is not always predictive of the final phenotype.
Environmental influences on coat color
A cat’s diet and environment can also impact coat color, especially melanistic black pigment. Cats with diets deficient in tyrosine (an amino acid needed to produce melanin) may fade from black to rusty brown. Exposure to extreme cold or sunlight can trigger increased melanin as well. Color fading can also occur with age, illness, or medical conditions impairing melanin synthesis. However, these environmental factors only modify a cat’s genetically predetermined coat shade. They do not alter the underlying genetic recipe.
The genetics of cat hair length
In addition to color, genes also determine hair length. Several mutations produce long-haired breeds like Persians, Maine Coons, and Turkish Angoras. The dominant L allele confers long hair. The recessive l allele results in short hair. When a cat inherits Ll, it will have semi-longhair known as a shaggy coat. Two copies of l produce a short smooth coat. Because the L longhair allele is incompletely dominant, two longhaired cats may still have a shorthaired kitten if both parents are heterozygous (Ll).
Conclusion
The varied coat colors and patterns seen in litters of kittens result from the complex interplay of multiple genes. Each kitten inherits a unique combination of alleles from its parents at loci controlling pigment production, tabby patterns, spotting, and hair length. Added randomness from new mutations also contributes to diversity. Understanding the feline genome provides insight into why cats from the same litter can exhibit such remarkable differences in their coats. While surprising to some owners, multicolored litters reflect the intricate genetics underlying one of nature’s most beautiful creatures, the domestic cat.
