(i) Mutations These are sudden heritable changes which are supposed to be the primary
source of genetic variation. They are of following two types

(a) Chromosomal Mutations They arise due to changes in chromosome number
and changes in structure.

(b) Gene Mutations These are changes in gene structure and expression due to
addition, deletion, substitution or inversion of nucleotides.

(ii) Non-random Mating Repeated mating between individuals of certain selected traits
changes the gene frequency, e.g., selection of more brightly coloured male bird by a
female bird may increase the gene frequency of bright colour in the next generation.

(i) Gene Flow (Gene Migration) It is the movement of alleles into and out of a gene pool
Breeding of immigrants with the host population adds new alleles to the gene pool of
the host population.