The rabbit coat color calculator above takes the genotypes of two rabbits at the five classical colour loci — A for agouti, B for black or brown pigment, C for full colour, D for density, and E for extension — and works out the probability of each coat colour appearing in a kit from that pairing. It names the resulting colours, ranks them, and converts each probability into an expected count for a litter size you choose.
Arb Digital publishes this as a genetics education tool. It predicts probabilities, not outcomes, and it says nothing about which rabbits should be paired. Decisions about breeding animals, and about the health and welfare of any rabbit, are matters for the owner in consultation with a veterinary surgeon and the relevant breed body — not for a probability calculator.
What This Rabbit Coat Color Calculator Does
Each locus is inherited independently, so the tool treats the cross as five separate one-gene crosses and multiplies the results together. At each locus a parent contributes one of its two alleles at random, giving the familiar three-outcome distribution for a heterozygous pairing. Combining five of those gives up to 243 genotype combinations, which the tool groups into the far smaller number of visible colours.
The visible colour is not simply the sum of the loci, because two of them are epistatic — they mask what the others are doing. The C locus, when homozygous recessive, prevents pigment production entirely and produces a ruby-eyed white rabbit regardless of everything else in the genotype. The E locus, when homozygous recessive, switches the coat to the red and yellow pigment series, so the B and A loci express differently. The calculator applies both of those precedence rules before naming a colour.
Boundary worth stating: this page applies a fixed, rabbit-specific gene set and names real colours. For generic inheritance problems — any one, two or three-gene cross in any organism, with the grid drawn out — use the Punnett square calculator, which is the general-purpose tool.
How to Use It
- Set the sire's genotype at each of the five loci. If you only know the visible colour, you may not know whether a dominant-looking locus is homozygous or heterozygous.
- Set the dam's genotype the same way.
- Enter a litter size to see probabilities converted into expected counts.
- Read the bars as a distribution. The headline colour is simply the most probable one, and where several are close, the headline is not meaningful on its own.
- Treat unknown genotypes as unknown. Guessing that a coloured rabbit is homozygous when it might be a carrier changes the answer substantially.
The Loci and What They Do
Rabbit colour genetics has been worked out at the molecular level for several of these loci. A 2022 study in Genetics, Selection, Evolution, Genomic diversity and signatures of selection in meat and fancy rabbit breeds, identifies the genes behind three of them: mutations in the melanocortin 1 receptor gene, MC1R, produce the alleles at the extension locus; mutations in the agouti signalling protein gene, ASIP, produce the recessive black non-agouti and tan alleles at the agouti locus; and several alleles at the albino locus arise from mutations in the tyrosinase gene, TYR.
A — agouti. The dominant allele gives banded hair shafts, the wild-type chestnut appearance. The recessive gives a self-coloured rabbit with the same pigment right through the shaft.
B — black or brown. The dominant allele produces black eumelanin; the recessive produces the brown form, which turns black into chocolate and blue into lilac.
C — colour. The dominant allele allows full pigment production. The recessive, when homozygous, blocks it altogether, giving a ruby-eyed white rabbit that carries but does not show its other colour genes.
D — density. The dominant allele gives dense pigment; the recessive dilutes it, turning black into blue and chocolate into lilac.
E — extension. The dominant allele extends the dark pigment across the coat. The recessive, homozygous, restricts it, leaving the red and yellow series — orange, fawn, tortoiseshell and smoke pearl.
How the Probabilities Combine
Because the loci assort independently, the probability of a particular combination is the product of the probabilities at each locus. Working the default values through: both parents heterozygous at all five loci means each locus has a three-in-four chance of showing the dominant phenotype. Chestnut agouti requires the dominant phenotype at all five, so its probability is 0.75 multiplied by itself five times, which is 243 in 1,024, or about 23.7 percent.
Ruby-eyed white is simpler, because it depends on one locus only. Two Cc parents give a one-in-four chance of cc, so a quarter of the kits are expected to be ruby-eyed white whatever else is in the cross. That is a useful illustration of epistasis: a single locus can account for a large slice of the probability distribution on its own, because it overrides everything downstream of it.
Where This Simplified Model Stops
Three of these loci carry more than two alleles in reality. The C locus is a dominance series that includes the chinchilla and Himalayan alleles as well as full colour and albino, which is why chinchilla and pointed rabbits exist and cannot be produced by a two-allele model. The A locus includes the tan allele between agouti and self. The E locus includes steel and Japanese brindle variants — a 2011 study identified a six base-pair in-frame deletion in MC1R associated with the Japanese brindling colour, and a genome-wide association study of coat color in Chinese Rex rabbits confirms ASIP's role in the non-agouti black coat.
Beyond the five loci there are separate genes for white spotting, Dutch marking, vienna and wideband patterns, each of which changes the appearance without touching the colours modelled here. And breed standards name colours differently: what one registry calls chestnut another calls castor, and shade descriptions vary between breeds. A calculator can give you the genetics; it cannot give you a show name.
Why the Expected Counts Are Not Predictions
The expected count is a probability multiplied by litter size, and it is an average across many litters rather than a forecast for one. Each kit is an independent draw, so an eight-kit litter from a cross with a one-in-four probability yields the expected two kits of that colour only about 31 percent of the time. It produces none at all roughly one litter in ten.
Small samples behave like this and no amount of arithmetic changes it. A cross that produced no chestnut kits in a litter of six is not evidence that the parents' genotypes were misidentified; it is an entirely ordinary outcome. Judging a genotype from a phenotype in one small litter is exactly the situation where probability intuition tends to fail, and it is why breeders track results across many litters rather than one.
Arb Digital publishes hundreds of free, no-signup tools covering genetics, animals, science and everyday maths — no accounts, no stored data.
Browse All Free Tools Contact Arb DigitalCommon Mistakes to Avoid
- Assuming a coloured rabbit is homozygous. A rabbit showing a dominant phenotype may carry the recessive allele, and that changes every probability downstream.
- Reading a probability as a guarantee. A one-in-four chance produces no such kits in a litter of six about eighteen percent of the time.
- Expecting the five-locus model to explain every rabbit. Chinchilla, Himalayan, tan, steel, broken and Dutch patterns all sit outside it.
- Matching a calculated colour to a breed standard name. Registries and breeds use different names for the same genetics.
- Treating a colour prediction as a reason to pair two animals. Which rabbits are bred, if any, is a decision about the animals and their welfare, not about their coats.
Related Free Tools From Arb Digital
For inheritance problems in general, the Punnett square calculator draws out monohybrid and dihybrid grids for any organism. Elsewhere on the rabbit side there is the pet age calculator, the pet enclosure size calculator and the animal gestation calculator. For the arithmetic, the percentage calculator converts probabilities to counts and the mutation rate calculator covers a different corner of genetics. Browse the full free online tools hub for more.
Frequently Asked Questions
A for agouti, B for black versus brown pigment, C for full colour, D for pigment density, and E for extension. Molecular work has linked the extension locus to the MC1R gene, the agouti locus to ASIP and the albino locus to tyrosinase.
Treat each locus as an independent cross, work out the probability of each genotype at that locus, then multiply across the five loci. Two rabbits heterozygous at all five loci give chestnut agouti a probability of 0.75 to the fifth power, about 23.7 percent.
Because the C locus is epistatic. When homozygous recessive it prevents pigment production altogether, giving a ruby-eyed white rabbit that still carries its agouti, black-brown, density and extension alleles and can pass them on.
The dominant allele extends dark pigment across the coat. When homozygous recessive it restricts it, leaving the red and yellow pigment series, which produces orange, fawn, tortoiseshell and smoke pearl depending on the agouti and density loci.
No. These are probabilities and each kit is an independent draw. A litter of eight from a one-in-four cross contains no kits of that colour roughly one time in ten, which is entirely ordinary rather than evidence of a mistake.
Because they come from additional alleles in the C dominance series, and this tool uses the simplified two-allele model at each locus. The same limitation applies to tan at the A locus and steel at the E locus.
Not always. Registries and breeds use different names for identical genetics, and shade descriptions vary. The names here describe the genetics; a show classification should come from the standard for that breed.
This calculator applies a simplified Mendelian model to genotypes you supply and predicts probabilities, not outcomes. It offers no guidance on whether any animals should be bred. Decisions about breeding, and about the health and welfare of any individual rabbit, should be taken with a veterinary surgeon and the relevant breed organisation.
