Grey plumage colouration in the duck is genetically determined by the alleles on two different, interacting loci.

Based on the observation of a grey phenotype in the F(1) generation from a cross between two white plumage duck varieties, the white Kaiya and the white Liancheng, we hypothesized a possible interaction between two autosomal loci that determine grey plumage. Using the parental and F(1) individuals, seven testing combinations including five different F(1) intercrosses (F(2)) and two different backcrosses (BC(1) and BC(2)) were designed to test our hypothesis. It was demonstrated by chi-squared analysis that six test matings produced offspring in the expected ratios between the grey and white, with P-values ranging from 0.50 to 0.99. Another mating, where all white offspring were expected, produced 33 white individuals. These results verified that the interaction between two loci produced the grey phenotype. The C locus, which carries the recessive allele (c), was previously thought to be the only gene responsible for white plumage in the duck. This is the first report that an allele (t), carried by the white Liancheng at a different autosomal locus, also determines white plumage in ducks. Furthermore, the dominant alleles at both loci can interact with each other to produce the grey phenotype, and a new dark phenotype, observed in some F(2) individuals, can be attributed to the dosage effect of the T allele.