The presence of feathers in dinosaurs and birds indicates that they are evolutionarily related. Dinosaurs had feathers not for flying but instead these feathers provided
insulation to these warm-blooded animals. However, the feathers in birds are used for flight. This proves that reptiles and birds are closely related and that the evolution of
wings started in reptiles.

Those organs which have the same basic structure but different functions are called homologous organs.
The wings of a butterfly and the wings of a bat cannot be regarded a homologous because they have different basic design though they are used for the same purpose of flying. 

Variant genotypes can be produced by
(a) Mutation in genes and chromosomes.
(b) Recombination of genes.
(c) Hybridization of genes.

The main difference lies in the difference in the sex chromosome of sperm (male gamete) and egg (female gamete). The main difference between sperms and eggs of humans is that half of the sperms of a male (father) will have X chromosomes and the other half will have Y chromosomes. All the eggs of female (mother) will have only X chromosomes.
Importance.
(a) If the father contributes X chromosome, then the baby born will be a girl.
(b) If the father contributes Y chromosome, then the baby born will be a boy. Thus, the sperm determines the sex of a child.

(a) It plays an important role in organic evolution because it is parallel to natural selection.
(b) It helps to produce new species having useful traits in less time.