Migration

• It refers to the movement of some individuals of a population into another population and their intermating with the individuals of the latter.
• Migration may lead to change in gene frequency depending upon :

I. Migration ratio = Proportion of migrant individual / total number after migration of individual

ii. The difference between gene frequencies of migrant individual and that of population into which migration has occurred.

Mutation

• A sudden heritable change ( not produced by segregation or recombination) in the characteristics of an organism is called mutation.
• It may be non recurrent or recurrent.

i. Non-recurrent mutation:

• It takes place only once. i.e. the same mutation willn’t occur in a future generation of a population.
• So, if there is a non-recurrent mutation in a gene, the mutant allele will be lost in one of the subsequent generation.

ii. Recurrent mutation:

• When a given mutation occurs regularly although at a very low frequency, it is called recurrent mutation.

iii. Selection:

• It is defined as differential rates of reproduction of different genotypes in a population.
• When differential reproduction is the consequences of natural factors, it is called natural selection and when it is brought about by human efforts, it is termed as artificial selection.
• Selection may operate on gametes or the haploid (n) phase (gametic selection) or it may acts on zygotes or the diploid ( 2n) phase ( Zygotic selection).

iv. Random drift:

• Random fluctuation in gene frequencies of a population due to chance or sampling error is called random genetic drift.
• Change in gene frequency due to drift doesn’t occur in same direction in all generation.
• Random drift is greater in smaller population than in larger one.
• Random drift is the consequence of sampling error.
• The rate at which genes become fixed in a population is estimated by formula 1/2 N and is called ‘rate of fixation’.
• Under certain circumstances, random drift may produce notable changes in gene frequencies ever in the face of selection or migration from other population.