Question

Find the species in which females are heterozygous having (ZW) chromosomes?
A.humans
B.birds
C.cow
D.bat

Answer 1

Heterogametic sex or digametic sex refers to the sex of the species in which the sex chromosome are not of the same type. The heterozygous genotype includes the individuals which contain identical forms of one gene from each parent. They are in contrast with the homozygous genotype identical.

Complete step by step answer:
Normally the females are having only two X chromosomes and the males are having both X and Y chromosomes. In many species the female is determined by the presence of two X chromosomes are called as heterogametic sex. The males have X and Y chromosomes and can produce different gametes. In the heterozygous condition, the bird females have Z and W chromosomes. Some of the reptiles are also seen in the heterogametic condition.
Additional information: Heterogamesis can lead to reduced or absent meiotic recombination between the sex chromosomes, and in some species this extends to the autosome, a phenomenon called achiasmy. For example, most lineages of male Drosophila melanogaster flies are achiasmy, lacking recombination on all chromosomes, although female show recombination

Hence the correct answer is option(B)

Note: This type of chromosomal system determines the sex of offspring’s in birds, some of fishes, insects and butterflies also. In this system, females show ZW pairs of chromosomes and males show ZZ pairs of chromosomes. No genes are shared between the avian ZW and mammalian XY chromosomes and from a chromosomes between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in humans, rather than X or Y, leading researchers to believe that the ZW and XY sex determination systems do not share an origin, but that the sex chromosomes are derived from the autosomal chromosomes of the common ancestors.