Explain the chromosomal basis of sex-determination in animals.

Explanation

The various mechanism of sex-determination in animals is described below:
(i) XX-XY type mechanism Females are homogametic and produce egg with only X-chromosomes. Males are heterogametic and produce sperms with X or Y thus determining the sex of the child.
(ii) XX-XO mechanism Here only X-chromosome is present and Y is absent.
The female is homogametic (XX) and the male is heterogametic (XO). Maleness is determined by a single X-chromosome, e.g.. grasshopper and bug.
(iii) ZW-ZZ mechanism In this mechanism, the female is heterogametic (ZW), while the male is homogametic (ZZ). The inheritance of Z and W chromosomes occur in a simple Mendelian fashion, e.g. birds.
(iv) ZZ-Zo mechanism In Lepidoptera (e.g. moths and butterflies), the male is homogametic with two Z chromosomes (ZZ) while the female is heterogametic with one each of Z and W-chromosomes (ZW). However, some females have ZO complement indicating that Wis not essential for femaleness.
(v) Haplo diploidy mechanism The female is diploid and male is haploid. Haploid male is produced when the egg is not fertilised. This type of development is termed as parthenogenesis. However, fertilised eggs develop as females, e.g. Honeybee, wasp, etc.