In Lake Malawi cichlid fish, one can observe two color variants, Black Barred (

Question

In Lake Malawi cichlid fish, one can observe two color variants, Black Barred (BB) and Orange Blotch (OB). Sex in these fish is not determined by a sex chromosome, but by a gene on an autosome, which produces either males or females. Both of these phenotypes are controlled by one biallelic locus each. OB females have a selective advantage in terms of their survivability: The OB phenotype allows females to blend into their background. OB males have a selective disadvantage because their reproductive coloration is disrupted and they have little mating success. How would this process influence the association of alleles at the color locus and sex determining locus?

Explanation / Answer

The Orange Blotch (OB) gene favors females while it makes disadvantages in males. Therefore, the genetic system of the Lake Malawi cichlid fish would not select OB gene for survival of males. This gene whenever comes in pair it will form a female. Therefore, the homozygous OB OB genotype is for females.

The OB BB genotype, the males will not get full characteristics of males and become a waste. Therefore, for the males’ development BB BB genotype will be choose by the genetic system.

This also suggests that females get only type of genotype OB OB, while males get two types of genotype BB BB and OB BB. Both types of males would survive but complete male individual will be BB BB.

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