By what name is the branch of biology related to the study of heredity and variation known as?

In human males,all the chromosomes are paired perfectly except one. These unpaired chromosomes are:
$(i)$ Large chromosome
$(ii)$ Small chromosome
$(iii)$ $Y$-chromosome
$(iv)$ $X$-chromosome

There is a sub-population $A$ and another sub-population $B$. Both are separated by a natural barrier. What will happen in such a case?

Give reasons for the following:
$(a)$ Traits acquired during the lifetime of an individual are not inherited.
$(b)$ All human beings belong to a single species.
$(c)$ Variations keep on accumulating during reproduction and do not disappear in the next generation.

From the list given below,select the character which can be acquired but not inherited.

There is an inbuilt tendency to variation during reproduction,both because of errors in $DNA$ copying,and as a result of sexual reproduction.