Rabbit Color Calculator

Rabbit coat color results from a few interacting loci that determine which pigment is produced, how densely it is deposited, and how it is banded along the hair shaft. This tool models two of them. At the agouti locus the dominant A allele produces banded hairs with a lighter belly, while the recessive a gives self color. At the dilution locus the recessive homozygote dd causes pigment granules to clump within the shaft, so black becomes blue, chocolate becomes lilac, and chestnut agouti becomes opal. Molecular work has assigned these to the agouti signaling protein gene and to melanophilin respectively. Because the two loci assort independently, the probability of a combined phenotype is the product of the single-locus probabilities: crossing Aa by Aa together with Dd by Dd yields the classic 9:3:3:1 dihybrid ratio of 56.25 percent chestnut, 18.75 percent opal, 18.75 percent black and 6.25 percent blue. The main limitation is deliberate simplification. Real coat color also involves the B locus (TYRP1, black versus chocolate), the C locus with its chinchilla, Himalayan and albino series at tyrosinase, the E or extension locus at MC1R, plus spotting and wideband modifiers, so a two-locus prediction can name the wrong show variety even when the underlying arithmetic is correct. Probabilities apply independently to each kit, so a litter of six from Aa by Aa parents frequently departs from the expected 4.5 to 1.5 split; binomial spread is wide at small litter sizes. In practice the largest error source is that parental genotypes are inferred from pedigree and test matings, not sequenced.

The grid used here was devised by Reginald Punnett at Cambridge in the first decade of the 20th century as a teaching device for Mendelian ratios, developed alongside William Bateson, who was championing Gregor Mendel's 1866 pea paper after its rediscovery in 1900. The rabbit became a principal mammalian subject for that new genetics almost immediately. William Ernest Castle, working at Harvard's Bussey Institution from around 1905, used rabbits to test whether Mendelian inheritance applied to mammalian coat color, and he and his students - Sewall Wright among them - established the A, B, C, D and E locus notation that breeders still use today. That notation passed from the laboratory into the fancy through breed clubs and show standards. The American Rabbit Breeders Association, founded in 1910 under an earlier name, standardized recognized color varieties, which made predicting the color composition of a litter commercially as well as intellectually useful. Molecular confirmation arrived decades later, as the genes behind the classical loci were identified one by one: tyrosinase for the albino series, TYRP1 for the brown locus, MC1R for extension, and in 2014 a research group led by Luca Fontanesi reported a mutation in the melanophilin gene as the cause of the dilute phenotype in rabbits. Sequence data thus confirmed what breeders had inferred from controlled crosses for roughly a century.