THE ENDOGENOUS RETROVIRAL EV21 LOCUS IN COMMERCIAL CHICKEN LINES AND ITS RELATIONSHIP WITH THE SLOW-FEATHERING PHENOTYPE (K)

Provirus ev21 was found in both K- and k+-feathering Rhode Island Red commercial layers. Probe EV21-int revealed the presence of two distinct but similar regions, US (unoccupied site) and OS (occupied site). Restriction analysis showed that these regions had at least 19 kb structural homology but were distinguishable by ev21 proviral sequences, OS, and possibly three polymorphics US. The loci OS and US were both located on Chromosome Z. The k+-feathering birds were found to have only one site (either OS or US) per individual Z chromosome, whereas K-feathering birds had at least one Z chromosome with both regions in cis configuration. It has been possible to show that the reversion to the k+-feathering phenotype is accompanied by the loss of either a US or OS region that disrupts the cis configuration in K-feathering birds.