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B Chromosome and Sex Determination in the Cichlid Fish

B chromosomes have a functional effect on sex determination in a species of cichlid fishes from Lake Victoria [...] The researchers found sex-ratio distortions caused by B chromosomes in the breeding line of the cichlids, as well as several protein-coding genes in the B chromosomes. The resultant ratio was female biased, suggesting a role for B chromosomes in female sex determination.

[...]

In the present study, the researchers performed an extensive analysis of B chromosomes in cichlid fishes from Lake Victoria to investigate their effect on cichlid evolution. Karyotype analysis of Lake Victoria cichlids suggested that, in one species, Lithochromis rubripinnis, there are female-specific B chromosomes. Crossbreeding experiments suggested that an effector of female sex determination in this species was the B chromosome. Furthermore, analyses of large-scale sequences of B chromosomes in Lake Victoria cichlids revealed multiple protein-coding genes in B chromosomes.

The sex determination gene was not found in this research. However, the researchers provide evidence that B chromosomes have a functional effect on sex determination and that they demonstrate a capacity to evolve into sex chromosomes.

from "B Chromosomes Affect Sex Determination in Cichlid Fishes"

Quoted on Mon Aug 22nd, 2011