Proc Biol Sci. Gynogenetic and sex-reversed cod populations have demonstrated a XX-XY sex determination system 213334but karyotyping of Atlantic cod and the closely related European hake Merluccius merluccius failed to reveal sex-linked chromosome heteromorphism 35 Mol Reprod Dev 80— Although the molecular mechanisms underlying many developmental events are conserved across vertebrate taxa, the lability at the top of the sex-determining SD cascade has been evident from the fact that four master SD genes have been identified: sry mammaliandmrt1 chickendmy medakaand DM-W Xenopus laevis [ 818 ].
Is a sex-determining gene s necessary for sex-determination in amphibians? The effects of genes carried only on the Y chromosome are, of course, expressed only in males. Table S2: Matrices of recombination rates. Arrows indicate turnovers in sex-determination systems. This deactivated X chromosome can be seen as a small, dark-staining structure—the Barr body —in the cell nucleus.
Figure 4 [ 4 ].
Temperature sex-reversal in amphibians and reptiles. Sex-chromosome turnovers: the hot-potato model. Methylation status of cMHM and expression of sex-specific genes in adult sex-reversed female chickens. Conserved sex chromosomes and karyotype evolution in monitor lizards Varanidae.
Anderson K. The X chromosome, being larger, carries many more genes than does the Y. Within gametologs, gene genealogy conforms to species genealogy. Estrogen appears to trigger sex reversal through the exclusion of sox9 from entering the nucleus in the somatic cells of the developing gonad of nonmammalian vertebrate.
Larval expression of zkY, zk1 and zk2 from hatching to juvenile stage. An exception is the novel salmonid sdY; a truncated male-specific copy of the interferon regulatory factor 9 irf9 , which is an immune-related gene not associated with sex In fact, the ovarian steroid production does not commence until almost days after birth.
The results of such an analysis may validate the common assumption that sex determination can be studied in isolation from other developmental processes which means that sex-determination modifiers can safely be assumed to have no other fitness effects.