In humans, there are two pairs of sex chromosomes.

$A$ guinea pig having black color,when crossed with a guinea pig having the same color,produced $80$ offspring,out of which $60$ were black and $20$ were white. Now,find out:
$(i)$ What is the possible genotype of the guinea pig?
$(ii)$ Which trait is dominant and which trait is recessive?
$(iii)$ What is this cross called,and what is its phenotypic ratio?

What indication do we get by the reappearance of dwarf plants in the $F_{2}$ generation?

Select the statements that describe characteristics of genes:
$(i)$ genes are specific sequence of bases in a $DNA$ molecule
$(ii)$ a gene does not code for proteins
$(iii)$ in individuals of a given species,a specific gene is located on a particular chromosome
$(iv)$ each chromosome has only one gene

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?

$(a)$ What is geographical isolation?
$(b)$ Illustrate the formation of a species with the help of an example where individuals become very different from each other and are no longer capable of reproduction among themselves.