THE ISOLATION OF CONSERVED DNA-SEQUENCES RELATED TO THE HUMAN SEX-DETERMINING REGION Y-GENE FROM THE LESSER BLACK-BACKED GULL (LARUS-FUSCUS)

The sex-determining region gene (SRY) is a recently discovered candidate for the mammalian testis determining factor (TDF). The gene appears to form part of a family with several autosomal representatives. I have investigated the occurrence of SRY-related sequences in birds. The polymerase chain reaction was used to isolate six homologues of the conserved motif of the SRY gene from the lesser black-backed gull (Larus fuscus). Female unique copies of the motif are apparently absent. Sequence similarity and phylogenetic parsimony methods suggest that, irrespective of avian or mammalian origin, SRY-type sequences fall into two subfamilies. This is consistent with the presence of two archetypal genes in an ancestor common to both taxonomic classes.