Changes in prolactin receptor homodimer availability may cause late feathering in chickens.

Chicken early (EF) and late feathering (LF) are sex-linked phenotypes conferred by wild-type k and dominant K alleles on chromosome Z, respectively. Besides prolactin (PRL) receptor (PRLR) and sperm flagellar 2 (SPEF2) genes, the K allele contains a fusion gene in which partially duplicated PRLR (dPRLR) and SPEF2 (dSPEF2) genes are linked in a tail-to-tail manner. The causative dPRLR gene encodes a C-terminal truncated receptor.