The sex determining loci and sex chromosomes in the family salmonidae.

Salmonids are descended from a common ancestor that underwent an autotetraploidization event. After a whole genome duplication species could deal with sex determination by deleting one copy of SEX, the sex determining locus, or by recruiting a duplicated transcription factor to become a novel sex determining gene. It is not known which if any of these strategies salmonids adopted, but it appears that they all have primarily a genetic mechanism of sex determination with male heterogamety. The sharing of sex-linked markers on the X and Y chromosomes and the difficulty in identifying Y-specific markers indicate that X and Y chromosomes in salmonids have a large pseudoautosomal region and a small sex determining region. Linkage analyses suggest that either SEX differs in different lineages or else has remained the same and moved by transposition to different chromosomes. The identification of the sex chromosomes in salmonid species has not resolved this issue. It is clear that salmonids are at an early stage in sex chromosome differentiation and therefore provide a wonderful opportunity to study the evolution of sex determination. The availability of a reference salmonid genome sequence would provide an important resource for research in this area.