White Chicken Genetics: Dominant vs Recessive White

"White" is the most misleading colour in the chicken. There is no white pigment; white is the near-total absence of pigment — and a bird can arrive there by at least two completely unrelated genes that work in opposite ways. That is why two white birds are not necessarily "the same" underneath, and why crossing them can throw coloured chicks. For the wider system, see the Genetics Guide.

White pullet with irregular black patches across the back and wing — the Paint pattern from Dominant White over a Blue/Splash base. — Dominant White over a Blue/Splash base gives the broken black-on-white "Paint" pattern.

Close-up of a chick's white down with warm gold-orange patches over the back. — The gold leakage Dominant White is known for, visible here in the down.

Completely clean white Brahma with no red or gold flecking, feathered legs. — A clean white with no flecking at all — the look the text above describes for Recessive White.

Close-up of pure white feathers with no coloured flecking. — No leakage anywhere in the feather, edge to edge — contrast this with the gold flecking two photos up.

Dominant White (I) — gene PMEL17

Dominant White (I) does its job with a single copy — it is dominant. Its gene is PMEL17, which builds the internal scaffold of the black-pigment granule; the mutation stops that scaffold forming, so eumelanin (black) fails to deposit.¹ Two things are characteristic of it:

It acts mainly on eumelanin (black). Pheomelanin (red/gold) is reduced but often leaks — this is why so many "white" birds carry flecks of red or gold in the hackle and shoulder.
It leaves eye pigment normal, because PMEL17 is specific to the feather melanosome.

Layered over a Blue or Splash base, Dominant White is also the basis of the "Paint" pattern.

The same PMEL17 locus also carries the Dun allele (I^D) — a sibling of I, not a separate gene — which dilutes black to a warm grey-brown rather than whitening it; its homozygote (I^D/I^D) is Khaki. Being incompletely dominant, Dun follows the same one-copy/two-copy pattern as blue → splash (dun → khaki), so a locus-mate of Dominant White nonetheless leaves a coloured, non-white bird.¹

Recessive White (c) — gene TYR (tyrosinase)

Recessive White (c) needs two copies (c/c) to show — a single copy is carried silently. It sits at a different gene entirely: TYR, tyrosinase, the enzyme at the very start of the pigment-making pathway. In recessive white a retroviral insertion in the tyrosinase gene suppresses its activity in the feather, so no pigment of either kind is laid down there.² Because the block is at the source, recessive white tends to give a cleaner white with little or no leakage — though the eyes usually stay pigmented, since this allele affects the feather rather than switching tyrosinase off everywhere (that is a related allele in the same series, albinism).

Side by side

	Dominant White (I)	Recessive White (c)
Gene	PMEL17 (melanosome protein)	TYR / tyrosinase (pigment enzyme)
Inheritance	Dominant — one copy shows	Recessive — needs two copies
Acts on	Mainly eumelanin (black)	All pigment at the source
Red/gold leakage	Common	Usually little to none
Carried hidden?	No — always visible	Yes — carriers look coloured

Why two white birds can give coloured chicks

This is the trap the two genes set. Neither white erases the colour genes underneath — they only hide the result — so a white bird can be carrying a full colour genotype that its own white gene is masking. Put two whites together and the masks can come off:

A Dominant White bird is often heterozygous (I/i+) on a coloured base. A Recessive White bird (c/c) has colour hidden under it. Cross them and some chicks inherit neither white in a masking combination — and appear coloured.
Crossing recessive white × a coloured non-carrier gives an all-coloured F1 (every chick a carrier); recessive white then reappears in about a quarter of the F2.

The practical upshot. "White" tells you almost nothing about a bird's genotype on its own. If you are breeding whites and getting surprise colour, you are probably mixing the two white genes, or breeding from Dominant White carriers with colour underneath. Work the actual genotypes through the Breeding Outcomes tool rather than assuming white breeds white.

Telling them apart

Without a test mating, the best visual clues are leakage and inheritance: a bird showing red or gold flecking on an otherwise white body is likely Dominant White (the leakage is its signature), while a consistently clean white that appeared only when two coloured-looking parents were crossed is likely Recessive White (it had been hidden in both carriers). A test cross to a known coloured bird settles it: Dominant White passes white to about half the chicks in one generation, whereas recessive white stays hidden until two carriers meet.

References

Kerje S et al. (2004) The Dominant white, Dun and Smoky color variants in chicken are associated with insertion/deletion polymorphisms in the PMEL17 gene. Genetics 168:1507–1518.
Chang C-M et al. (2006) Complete association between a retroviral insertion in the tyrosinase (TYR) gene and the recessive white mutation in chickens. BMC Genomics 7:19.

Try it: work a white cross · Paint vs Splash · read the Genetics Guide