The distinctive color is caused by the action of an autosomal recessive gene, commonly designated as " " lav " ", which reduces the expression of eumelanin and phaeomelanin so that black areas of the plumage appear pale grey instead, and red areas appear a pale buff.
22.
Closely tied to this process, the role of the Agouti gene is to produce Agouti signalling peptide " Asip ", which disables " Mc1r ", effectively allowing the red pigment phaeomelanin to " show through . " However, this disabling does not occur throughout the coat; it occurs only in pulses on the body coat and not at all on the extremities or " points ".
23.
The " lavender " gene ( " lav " ) in the chicken causes the dilution of both black ( eumelanin ) and red / brown ( phaeomelanin ) pigments, so according to color background, dilution due to " lavender " gives a sort of plumage color patterns : On an extended black background, this condition causes the entire surface of the body an even shade of light slaty blue, which is the typical phenotype known as'" self-blue " '.
24.
The primary gene for coat color ( B ) for the colors brown, chocolate, cinnamon, etc ., can be masked by the co-dominant gene for the orange color ( O ) which is on the X Chromosome and has two alleles, the orange ( "'X O "') and not-orange ( "'X o "'), that produce orange phaeomelanin and black eumelanin pigments, respectively . ( NOTE : Typically, the "'X "'for the chromosome is assumed from context and the alleles are referred to by just the uppercase "'O "'for the orange, or lower case "'o "'for the not-orange . ) The tortoiseshell and calico cats are indicated : "'Oo "'to indicate they are heterozygous on the "'O "'gene.
