HARDY WEINBERG EQUILIBRIUM

It states that allele and genotype frequencies in a population will remain constant from generation to

generation in the absence of other evolutionary influences.

THE HARDY-WEINBERG PRINCIPLE STATES: Genetic equilibrium will be reached if

the frequency of alleles remains stable generation after generation.

Genetic equilibrium = no evolution occurring.

It allow us to predict allele frequencies in living population.

The Hardy-Weinberg principle assumes that in a given population, the population is large and is not experiencing mutation, migration, natural selection, or sexual selection.

In the simplest case of a single locus with two alleles denoted A and a with frequencies f(A) = p and f(a) = q, respectively,

the expected genotype frequencies are f(AA) = p2 for the AA homozygotes, f(aa) = q2 for the aa homozygotes , and f(Aa) = 2pq for the heterozygotes .The genotype proportions p2, 2pq, and q2

are called the Hardy-Weinberg proportions.

KEY POINTS:

The frequency of alleles in a population can be represented by

p + q = 1 The frequency of genotypes in a population

can be represented by p2 +2pq+ q2= 1 Gene pool :total genes and their alleles in a

population, that remain constant.

DIAGRAMMATIC REPRESENTATION OF THE OPERATION OF NATURAL SELECTION ON DIFFERENT TRAITS

HARDY-WEINBERG EQUILIBRIUM DESCRIBES POPULATIONS THAT ARE NOT EVOLVING.

Genotype frequencies stay the same if five conditions are found: very large population: no genetic drift no emigration or immigration: no gene flow no mutations: no new alleles added to gene

pool random mating:

no sexual selection no natural selection:

all traits aid equallyin survival

GENETIC DRIFT When migration of a section of a population

to another place and population occurs , gene frequencies change in the original as well as in the new population.

New genes/alleles are added to the new population and these are lost from the old population.

If this gene migration , happens multiple times then it is gene flow but if the same change occur by chance,

then it is called as genetic drift.

SEWALL WRIGHT EFFECT Standard deviation expression to

calculate allele frequency deviation in different population sizes

σ =√pq/N p = freq. of allele Aq = freq. of allele aN = no. of genes sample for diploid parents carrying 2 alleles σ = √pq/2N

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