Principles of Genetics and Breeding

4.1.7.5 Multiple sex chromosomes

1. X₁ X₂ X₂ – females, X₁ X₂ Y– males.

E.g. Megupsilon aporus (File fish),Cyprinodon sp.

2. ZZ / ZW₁ W₂. Multipe W chromosomes are present.

ZZ–males, ZW₁ W₂ – females

E.g. Apareiodon affinis

3. XY₁Y₂ males, XX – females.

E.g. Hoplias sp.

• In this system the number of chromosomes is not constant within a species.
• In the first two cases, females have one extra chromosomes. In the third, males have one extra chromosomes.

• Sex determination in fish that have sex chromosomes is not really a simple. Although sex in these species is controlled by the sex chromosomes, an individual’s sex can also be influenced or controlled by autosomal sex-influencing or sex-modifying genes (as in the case of tilapia).