Chicken Genetics for Dummies

Dominant white inhibits black pigment (eumelanin) but does not affect red/yellow pigment (pheomelanin). Because of this, Ermine, Paint and Dominant White birds may show gold leakage or khaki tones, which should be selectively bred away to maintain a clean pattern.

This gene is incompletely dominant—one copy (I/i+) suppresses most some of the eumelanin, while two copies (I/I) suppresses it completely, typically resulting in an all-white bird.

Blue is a black diluter gene and is also an incomplete dominant gene.

"Blue" birds carry one copy (Bl/bl) and "Splash" birds carry two copies (Bl/Bl) of the blue gene. Birds carrying a single copy of the gene can show a range of expression, from dark to light Blue, while those with two copies are Splash, appearing almost white with scattered blue markings.

Mottling is a recessive gene.

Mottling is a genetic trait where the tips of a bird’s feathers lose melanin, resulting in distinct white markings. This pattern develops over time, with birds typically gaining more white after they go through their adult molt.

The mottling gene should not be confused as Mottled—the variety. Mottled is influenced by mottling, but as a recognized variety, Mottled follows the SOP for uniformity in pattern, color, and overall appearance.

Check out our Mottled Silkies and Satins for visuals!

The pea comb gene is dominant. A bird with one or two copies of the pea comb gene will have a pea comb. However, birds with two copies (PP) may have a more pronounced pea comb than those with just one copy (Pp). 

The rose comb gene is dominant. A bird with one or two copies of the rose comb gene will have a rose comb. However, birds with two copies (RR) may have a more pronounced rose comb than those with just one copy (Rr).

Walnut combs result from the combination of pea comb and rose comb genetics. However, because both the pea comb and rose comb genes are located on the same chromosome, it becomes lethal when both genes are homozygous (PPRR).

Embryos that inherit two copies of each gene typically do not survive and will die before hatching. This is one reason why walnut combed breeds can never fully eliminate single comb genetics (or incorrect combs in general) and why their hatch rates are often lower than those of other breeds.

Single comb is considered a recessive trait. The genotype pprr represents the absence of both pea and rose comb genetics. The p allele indicates the absence of the pea comb gene, while the r allele indicates the absence of the rose comb gene. Therefore, pprr is the complete absence of both pea and rose comb traits, resulting in the expression of single comb genetics.