Initial clues about the genetic/chromosomal mechanism of sex determination can be traced back to some of the experiments carried out in:

Barr body in mammals represents

In the given figure, the part indicated by $B$ is produced by which process?

Assertion : In humans,the gamete contributed by the male determines whether the child produced will be male or female.
Reason : Sex in humans is a polygenic trait depending upon a cumulative effect of some genes on $X-$ chromosome and some on $Y-$ chromosome.

Give differences: Male heterogamety and Female heterogamety.

$A$ man receives his $X$ chromosome from