Endogenous viral genes in a slow-feathering line of White Leghorn chickens.

Endogenous viruses related to avian leukosis viruses were characterised in three sire families of slow-feathering White Leghorns. Progeny released infectious endogenous virus when extracts were tested on subgroup E susceptible fibroblasts. Restriction fragment length polymorphisms (RFLPs) indicated germline transmission of ev1, ev5, ev21 and a hitherto unreported locus ev22 among three sire families. The association of ev21 with the release of infectious endogenous virus precluded phenotypic characterisation of ev22 present in a third family.