Question

Write the types of sex-determination mechanisms for the following crosses show. Give an example of each type.
1. Female XX with male XO
2. Female ZW with male ZZ

Answer 1

Hint: Sex determination is the process of sex differentiation by which whether a particular individual will develop into male sex or female sex. Sex expression is governed by chromosomes and genes. In unisexual animals, chromosomes are two types, viz., autosomes and allosomes.

Complete Answer:
1. The female XX with male XO, female has double X chromosomes (XX) and male has single X chromosome (XO). Female is homogametic and produces all eggs with an X chromosome. The male is heterogametic, which produces sperms, half of which have X chromosome and another half have none. Union of egg with sperm having X chromosome will give rise of female sex and with sperm having non results in development of male sex. It is seen in organisms like grasshoppers, many orthoptera, hemipteran insects.

2. The female ZW with male ZZ, female is heterogametic and produces two types of gametes Z and W types. Male is homogametic and produces all sperm of the same type carrying one Z chromosome. Union of Z sperm with ovum having Z chromosome gives rise to male and union of Z sperm with ovum carrying W chromosome leads to development of female sex. It is seen in organisms like butterflies, birds and moths.

Note: Heterogametic sex chromosomes do not match and thus the gametes produced by that sex do not match. Homogametic sex chromosomes match and will produces the same sex- ed gametes. Important mechanisms of sex determinations are sex character, chromosomal sex determination, monogenic sex determination, environmental sex determination.