Question

Three Mark Questions :
(i) Why are Grasshopper and Drosophila said to show male heterogamety? Explain.
(ii)Explain Female heterogamety with the help of an example.

Answer 1

In grasshopper and Drosophila, there is male heterogamy. In those the females have allosomes as XX. In X chromosome there is a gene called SRY. In males there is one X. Chromosome and so there's gene produce testis. Female heterogamety:- In females there are chromosomes as XX. there are two genes. These genes form ovary in those organisms. In most of species like birds, moths and some fish a chromosomal mechanism of sex determination occurs that is basically identical to the XX-XY mechanism. As females are heterogametic it is designated as ZW. The males being homogametic, they are designated as ZZ. This is referred as ZZ-ZW type instead of XX-XY system. It is common in insects, vertebrates like fish reptiles, birds, etc. Females are heterogametic with ZW and males are homogametic with ZZ. Female produces two types of eggs, i.e., 50% with ‘Z’ or 50% with ‘W’ while male produces only one type of sperms, i.e., with ‘Z’. The sex of the offspring depends on the type of egg it was fertilized.