Principles of Genetics and Breeding

4.1.7.7 A typical sex determination

There exist a number of instances of atypical sex determination in fishes and they share the phenomenon of incomplete penetrance, i.e., individuals with the same genotype for atypical sex determination may develop into either male or female.

• The physiological basis for this labile determination of the undifferentiated gonad is not known.
• It should be determined whether fishes with genotypes for ASD are susceptible to still unrecognized environmental influences on sex determination.
• In all species of Xiphophorus sporadic instances with the sex chromosome constitution typical of females, XX, WX, or WY, differentiate into functional males, and XY individuals develop into functional females.
• The phenomenon of atypical sex determination has a genetic basis and each instance is caused by the interaction of an autosomal factor with a specific sex chromosome.
• When exceptional WX or WY males are mated with WY females, WW progeny are obtained that can develop into either males or females, and when exceptional XY females are mated to XY or YY males, the YY offspring may differentiate into either sex.