Most people start looking into cat genetics when they’re trying to make sense of something concrete: a tortoiseshell kitten in a litter of tabbies, a rare male calico, a breeder’s claim about “dominant traits”, or a DNA test report with unfamiliar gene names. The details matter, because genetics can shape not only how a cat looks, but also the risk of inherited disease in some breeds.
Below is a practical, plain-language guide to how feline traits are inherited, what coat colours and patterns can (and can’t) tell you, and where genetic testing helps most—without turning cats into simple gene charts.
Basics of cat genetics (what’s happening under the fur)
Genes, chromosomes, and what cats inherit
Genes are stretches of DNA that carry instructions for building and maintaining the body. They sit on chromosomes—long, packaged strands of DNA in nearly every cell. Domestic cats have 38 chromosomes in total: 18 pairs of autosomes plus the sex chromosomes (XX in most females, XY in most males).1
A kitten inherits one set of chromosomes from each parent, so most genes come in pairs. Different versions of a gene (alleles) can produce different visible traits, like coat colour or coat type, or influence health in less obvious ways.
Dominant, recessive, and “it’s complicated”
Some traits behave in a roughly dominant/recessive way: one allele can have a visible effect even when paired with a different allele. Others are influenced by multiple genes, by gene regulation, or by development itself—so they don’t follow tidy classroom rules.
Even when a trait is described as “dominant”, it may show incomplete penetrance (not every cat with the variant looks or is affected the same way) and variable expressivity (the degree of the trait can vary). Polydactyly is a good example.2
Common genetic traits you’ll notice
Coat colour and pattern: why tabbies are common
Many familiar coat features are shaped by a small set of well-studied genes—such as those affecting whether the coat shows banded “agouti” hairs (often linked to tabby pattern visibility), pigment type, colour dilution, and colourpointing. Practical summaries of these coat-colour genes (and how registries describe them) are published by veterinary genetics laboratories that also offer DNA testing.3
Calico and tortoiseshell: why they’re usually female
Calico and tortoiseshell patterns are tied to coat-colour variation on the X chromosome. Because most female cats have two X chromosomes, a normal process called X-chromosome inactivation can leave different skin cell lineages expressing different colour alleles, producing patches of orange and black (often with white spotting layered over the top). Male calicos are rare, and when they occur they are often associated with an atypical sex chromosome pattern (such as XXY), and are commonly sterile.4
Polydactyly (extra toes)
Most cats have 18 digits in total. Polydactyly means a cat is born with extra digits on one or more paws. It is typically inherited as an autosomal dominant trait, and in some lines it can show incomplete penetrance and variable expression—ranging from a small “thumb” to more substantial extra toes.2
Breeding and genetic diversity
Why genetic diversity matters
In any animal population, genetic diversity helps reduce the chance that harmful variants become concentrated. In pedigree breeding, the pressure to select for a particular look can narrow the gene pool. That doesn’t guarantee illness, but it does raise the odds that inherited disorders—or the same few risky variants—will turn up repeatedly.
Selective breeding: useful, but not free of consequences
Selective breeding can reliably produce certain coat types and body shapes, but it can also increase the frequency of inherited disease variants, especially when a small number of popular sires dominate a breed. Genetic screening, open health reporting, and careful mate selection are the main tools used to reduce that risk while keeping a breed’s defining traits.
Ethics: when a “look” is tied to pain
Some visible traits are closely linked to disease. The Scottish Fold’s folded ears, for example, are associated with a dominantly inherited cartilage and bone disorder (osteochondrodysplasia) linked to a TRPV4 variant, and affected cats can develop painful skeletal changes over time.5
Genetic disorders seen in cats
Hypertrophic cardiomyopathy (HCM)
Hypertrophic cardiomyopathy is the most common cardiac disease diagnosed in cats. In some breeds, specific variants are known to increase risk. In Maine Coons, a well-known example is the MYBPC3 A31P variant, which is associated with increased risk of developing HCM (with more severe, earlier disease possible in cats with two copies).6
A positive genetic result does not replace a veterinary exam or heart ultrasound, but it can help guide breeding decisions and monitoring.
Polycystic kidney disease (PKD) in Persians and related breeds
Feline PKD is commonly discussed in Persian and Persian-related cats and is consistent with autosomal dominant inheritance. Cysts can often be detected on ultrasound from a young age in affected lines, and the disease may progress over years.7
Breed predisposition is not destiny
Breed-associated risk means “more common than average”, not “guaranteed”. Many cats in predisposed breeds never develop the condition, and cats outside the breed can still be affected. The best approach is steady: know the risks, screen appropriately, and don’t guess based on appearance alone.
Genetic testing: where it helps (and where it doesn’t)
What DNA tests can tell you
Modern feline DNA tests can identify many known variants linked to coat traits and some inherited diseases. Laboratories also offer parentage testing in some contexts. The value is clearest when a test result changes a decision—such as whether to breed, how to monitor a known risk, or how to interpret an unusual phenotype.8
What DNA tests can’t do
- They don’t test for every possible disease variant—only the ones included in the panel.
- A “clear” result doesn’t guarantee a cat will never develop the disease (many conditions are multifactorial or have undiscovered variants).
- A “risk” result doesn’t confirm illness; it may indicate increased probability or carrier status, depending on the condition.
Practical takeaways for owners
- If you’re choosing a kitten from a breed with known inherited risks, ask for health screening details (test name, lab, date, and the parents’ results).
- If a DNA test flags a disease-associated variant, take the report to your vet and ask what monitoring makes sense for your cat (and when).
- Treat coat colour “personality stories” gently. Coat genes explain pigment and pattern far more reliably than behaviour.
Final thoughts
Cat genetics is easiest to live with when it stays grounded: a quiet set of rules, many exceptions, and a steady thread connecting appearance, inheritance, and health. When you use it well—especially in breeding and preventive care—it becomes less a curiosity and more a practical way to reduce avoidable disease while keeping cats as they are: varied, resilient, and never entirely predictable.
References
- The Feline Genome and Clinical Implications (includes domestic cat karyotype: 38 chromosomes)
- OMIA: Polydactyly in domestic cats (mode of inheritance; biological basis and notes on penetrance/expressivity)
- UC Davis Veterinary Genetics Laboratory: Feline coat colour overview
- UC Davis Small Animal Genetics Service FAQ (calico genetics; rarity of male calicos)
- Gandolfi et al. 2016 (PubMed): TRPV4 variant underlying osteochondrodysplasia in Scottish Fold cats
- UC Davis VGL: Hypertrophic cardiomyopathy (HCM) test information for Maine Coons (MYBPC3 A31P)
- Inheritance of polycystic kidney disease in Persian cats (PubMed)
- UC Davis Veterinary Genetics Laboratory: Cat testing menu (coat traits, parentage/genetic markers)
Veterinary Advisor, Veterinarian London Area, United Kingdom