Factors Affecting Hardy–Weinberg Equilibrium 

i. Gene migration or gene flow: When individuals migrate to another place or population, new genes or alleles are added to new population and are lost from old population, in turn changing the frequencies. When gene migration occurs many times, it is called gene flow. 

ii. Genetic drift: Changes occurring in frequencies by chance is called genetic drift. Sometimes, due to changes in allele frequency in new population, some form a different species. This effect is called founder effect and the original drifted population is called founder. 

iii. Mutation: Advantageous mutations lead to new phenotypes and over few generations, result in speciation. 

iv. Genetic recombination: During gametogenesis, variations due to recombination result in new phenotypes. 

v. Natural selection: Heritable variations that enable survival of the fittest will leave greater number of progeny. Natural selection can have following three effects: 

a. Stabilisation: Larger number of individuals acquire mean character value so peak gets higher and narrower. 

b. Directional change: Large number of individuals acquire value other than mean character value so peak shifts in one direction. c. Disruption: Large number of individuals acquire peripheral character values at both ends of the distribution curve and hence 2 peaks are formed.