Genetic variation in hyperpigmentation of an F₂ chicken population involving Kadaknath and White Rock chickens

The ‘Fm’ gene renders Kadaknath (KN) a unique breed among all native fowls of India, owing to its effect in overproducing black (melanin) pigments in skin and virtually all visceral tissues. A study was undertaken to delineate various pigmentation-phenotypes arising due to expression of alleles from two major skin-color loci: ‘Fm’ and ‘Id’ and evaluate their impact on growth and carcass-quality, involving an F₂ generation of Kadaknath-crossbreds derived from KN-White Rock (WR) crosses. A total of 230 F₂ chickens were reared till their slaughter at 10 weeks of age and evaluated for plumage patterns, skin-pigmentation, growth and carcass-quality traits. The results revealed four primary skin-pigmentation patterns among the F₂ progeny: (a) White (no traces of pigment), (b) un-pigmented with pinpoint black spots, (c) intermediate-black or Slaty and (d) intensely-black (fully-pigmented) skin color. A Chi-square analysis involving alleles from these skin-color loci, encompassing ratio of F₂ skin-color phenotypes revealed non-significant deviation between the observed and expected ratio. Analysis of variance comparing differences between two resultant skin-color phenotypes i.e. pigmented versus non-pigmented, pooled over the F₂-lot, yielded non-significant differences for both growth and carcass quality traits. The plumage-color patterns analyzed on F₂ progeny suggested secondary roles for the ‘C’ and ‘I’ loci in modulating the intensity of skin-pigmentation of resultant-phenotypes. It was concluded that hyperpigmentation of skin was primarily controlled by autosomal locus ‘Fm’ being subject to epistatic-interaction from sex linked ‘Id’ genes, where feather-pigmentation genes from ‘C’ and ‘I’ loci apparently played modifying roles.