Chickens have 2 kinds of pigment that help define their plumage color. These pigments are known as eumelanine (black pigment) and pheomelanine (yellow/red pigment).
One of the best studied eumelanin diluters is Dominant white (I). While the Dominant white (I) gene inhibits eumelanine (black pigment) well, it is a relatively ineffective inhibitor of pheomelanin (yellow/red pigment).
In the case of Dominant white (I), the following is produced:
1. (I/I) which results in a white phenotype
2. (I/i+) which results in a black-flecked phenotype
3. (i+/i+) which results in a black phenotype.
Modifying genes, which limit or expand the amount of black on a heterozygote, affect the overall number of black feathers present on the plumage. The modifying genes also affect whether the black plumage feathers will be solid black and the white plumage feathers solid white.
The Dominant white gene (I) can remove epidermal shank pigment and dilute dermal pigment. Poultry shanks contain two layers of skin known as the epidermal and dermal layers. The epidermal layer is the “top” layer of skin and the dermal layer is the “bottom” layer of skin. Dermal melanin (id), either in the homozygous or hemizygous condition, allows for the deposition of melanin in the dermis. Dermal melanin behaves in a sex-linked manner and is found on the sex chromosome. Research has shown that slate shanks can be achieved on Dominant white birds that are homozygous for Extended black (E) and Dermal melanin (id). Extended black is the most melanizing and dominant e locus allele. It “extends” melanin pigment into the shanks of fowl.
The Recessive white gene (c) can inhibit both eumelanine and phaeomelanin, but occasionally phaeomelanin may still leak through. The Recessive white gene dilutes melanic pigment in the shanks due to the absence of Chromogen.
In the case of Recessive white (c), the following is produced:
1. (c/c) which results in a white phenotype
2. (c/C+) which results in a black phenotype that carries one copy of the recessive white gene.
3. (C+/C+) which results in a black phenotype.
So what are some differences we can note regarding Recessive and Dominant white based on this educational post?
1. Recessive white inhibits pheomelanin more effectively than Dominant white.
2. The Recessive white (c) and Dominate white (I) genes dilute the epidural layer of skin on shanks.
3. Recessive white needs “less assistance” than Dominant white to create a solid white plumage color.
4. While Recessive white birds may carry either S or s+, silver is an important part of the genotype of Dominant white birds in order to create solid white plumage color.
