How can the chromosomes be identified?

$A$ 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?

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

Give differences between
$(a)$ Heredity and variations.
$(b)$ Dominant and recessive traits.
$(c)$ Natural and artificial selection.

New species may be formed if
$(i)$ $DNA$ undergoes significant changes in germ cells
$(ii)$ chromosome number changes in the gamete
$(iii)$ there is no change in the genetic material
$(iv)$ mating does not take place

When are the genetic traits of parents transmitted to the offspring?