Black cats are mysterious creatures that have captivated people for centuries. Their dark coats and striking eyes hold an allure that is hard to resist. Among black cats, those with brilliant blue eyes are particularly rare and special.
If you’re short on time, here’s a quick answer to your question: Black cats with blue eyes occur due to a gene mutation that causes excess melanin production early in development, which leaves the cats black-coated.
The blue eye color is caused by a separate gene mutation that reduces melanin production in just the eyes, allowing the blue eye color to show through.
In this comprehensive guide, we will explore the genetics behind black coats and blue eyes in felines. We will look at why this combination is so unusual and discuss breed preferences. Health considerations for these cats will also be covered.
The Genetics Behind Black Cat Coats
The Dominant Black Gene
The striking black coat of many cats is produced by a dominant gene called “black” or “B.” This gene codes for large amounts of black pigment, or melanin, in the fur. When a cat inherits one or two copies of the B gene, its coat will be completely black.
This is an example of complete dominance, where one copy of the dominant allele is enough to mask the effects of the recessive allele.
Melanocytes and Melanin Production
Melanin is produced by specialized cells called melanocytes in the skin and hair follicles. The B gene causes these melanocytes to churn out copious amounts of a protein called eumelanin, which results in black pigmentation.
Other genes can interact with B to produce additional fur colors like brown (chocolate) or cinnamon, but a cat with two B alleles will exhibit the archetypal jet black coat.
Complete Dominance
In the case of coat color genetics, the dominant B allele is completely dominant over other alleles that might lead to more diluted fur pigmentation. That’s why black coats are so common, even in mixed breed cats. Having just one copy of B is enough to confer a black coat.
According to the Cat Fanciers’ Association (CFA), over 22% of pedigreed cats have predominantly black fur. This illustrates the power of the dominant B gene in feline coloration.
The Genetics of Blue Eyes in Cats
Lack of Pigment Allows Blue to Show
A cat’s eye color is determined by the amount of melanin, or pigment, in the iris. Melanin comes in two forms: eumelanin which produces brown/black pigment, and pheomelanin which produces yellow/red pigment. The more melanin present, the darker the eye color.
If a cat has very little melanin in the iris, the natural blue color of the collagen fibers in the eye will show through, resulting in blue eyes.
The Alleles Responsible for Eye Color
In cats, there are two alleles or forms of a gene that are responsible for determining eye color:
- B – Dominant allele, produces melanin and results in orange, copper, hazel, green, brown or yellow eyes
- b – Recessive allele, produces little to no melanin, allowing blue eyes to show through
Cats that have the genotype BB or Bb will have melanin-producing eyes that are orange, green, hazel, etc. Only cats with the genotype bb will have blue eyes.
Blue Eyes as a Recessive Trait
Since the b allele responsible for blue eyes is recessive, blue eyes will only occur if a cat inherits two copies of the recessive b allele (bb genotype). If a cat inherits one dominant B allele and one recessive b allele (Bb genotype), the dominant B will be expressed and the cat will have melanin-producing orange, hazel, green eyes.
For a cat to be born with blue eyes, both parents must at least carry the recessive b allele. So two blue-eyed parents will always produce blue-eyed kittens. But even if just one parent has blue eyes, kittens can potentially be blue-eyed if the other parent carries the recessive b allele.
Here’s a table summarizing the genotypes and possible eye colors:
| Genotype | Eye Color |
|---|---|
| BB or Bb | Orange, copper, hazel, green, brown, yellow |
| bb | Blue |
Rarity of Black Cats with Blue Eyes
Each Mutation on Its Own is Uncommon
Individually, both the black fur gene and the blue eye gene are relatively rare in cats. The recessive black fur trait only occurs in about 35% of house cats, while blue eyes are found in around 5-10% of the overall feline population according to studies.
The black coat color develops from a mutation in the cat’s Agouti gene that causes overproduction of eumelanin pigment. This overrides the other color patterns and results in solid black fur. The blue eyes mutation affects the gene responsible for eye pigmentation.
Both Mutations Together Are Very Rare
Given the rarity of each trait, cats having both black fur and blue eyes at the same time are extremely unusual. The likelihood of these mutations coinciding is calculated as less than 0.05% chance or 1 in 2000 births if both parents carry one copy of the relevant mutated genes.
That said, their dazzling and distinctive looks make black cats with blue eyes highly desirable. Breeding programs focus specifically on producing more of these remarkable felines.
Breed Preferences
While possible in almost all breeds, black coats with blue eyes occur more frequently in certain pedigree cats. Breeds with higher instances include:
- Siamese – 20% have blue eyes with black points
- Bombay – Black coats, 15% have blue eyes
- British Shorthair – 10% overall occurrence
Mixed breed domestic cats rarely exhibit the combination. Yet when they do, these animals display a supernaturally-beautiful appearance.
Health Considerations for These Cats
No Health Issues Directly Related
Black cats with blue eyes are just as healthy as any other cat colors or eye colors. There are no health issues directly related to their unique coloration. Their fur and eye color is simply the result of genetics, not any underlying health problems.
These stunning kitties are not predisposed to any illnesses or disorders specifically due to being black with blue eyes. They have the same expected lifespan and health considerations as any other cat. With proper care and veterinary checkups, they can live long, healthy, and happy lives.
Potential for Deafness
One potential health consideration for black cats with blue eyes is an increased risk of deafness. However, deafness is not extremely common in these cats.
Deafness in cats is often caused by a lack of pigment cells in the inner ear. Since blue eyes and solid black coats result from a lack of pigment cells in the iris and fur, it follows that these cats may also lack pigment cells in their inner ears.
However, a major 2021 study found that only 17% of solid black cats with blue eyes were deaf. So while their risk is increased compared to other cat colors, most black cats with blue eyes will have normal hearing.
Responsible breeders will test kittens for deafness before homing them. If you adopt a black cat with blue eyes, be sure to have your vet test their hearing during their first exam.
Deaf cats can live full, enriching lives with some small adjustments by their owners. Providing consistent hand signals, keeping them indoors in a safe environment, and being cautious around loud noises can help deaf cats thrive.
So while deafness is a potential concern, it should not deter someone from adopting one of these striking kitties. With some simple precautions, even deaf black cats with blue eyes can live long and healthy lives.
Conclusion
Black cats with brilliant blue eyes are a striking combination. This rare pairing is made possible by two separate genetic mutations – one leading to excess black pigment, and one reducing pigment specifically in the eyes. These cats have captivated humans for centuries with their mystical allure.
While no health issues are directly linked to their coloration, potential hearing impairments may occur. With their rarity and beauty, black cats with blue eyes will continue to be prized possessions for fortunate feline fans.
