Organization of the sex-linked late-feathering haplotype in chickens

Nucleotide sequence analysis of polymerase chain reaction products confirmed that ev 21 integrated into one of two large homologous elements on the Z chromosome of late-feathering (LF) White Leghorn chickens. Southern blots of Not I-, Nae I-, Ksp I- and Bam HI-digested DNA from early-feathering (EF) and LF White Leghorns, that had been hybridized with a probe that flanks ev 21, indicated a 180 kb duplication of an unoccupied repeat in the LF genotype of White Leghorns. A Ksp I fragment that carries ev 21 was about 32 kb smaller than the Ksp I fragment found in EF DNA. In the evolution of LF, retroviral insertion into one of two large repeats and a 32 kb deletion may have generated LF.