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HARDY WEINBERG
PRINCIPLE
PREM SIDHARTH R
SUBJECT MATTER EXPERT (BIOLOGY-INTERNATIONAL)
FILO EDTECH
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LTD

INTRODUCTION
▪ In a given population one can find out the frequency of occurrence of alleles of a gene or a locus
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▪ Hardy-Weinberg principle stated it using algebraic equations
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▪ The gene pool (total genes and their alleles in a population) remains a constant
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▪ Sum total of all the allelic frequencies is 1
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e
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Such a population would be at equilibrium since the genotypic frequencies would be stable, that is, would not change, from
one generation to the next
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A population is said to be at equilibrium when frequencies of the three genotypes, AA, Aa and aa are p2 , 2pq and q2 ,

respectively
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There would be three genotypes, AA, Aa
and aa, for this gene in the population
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The total number of alleles at this locus in the population would be 2N
since each individual has two alleles at a single locus
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The ration (2D+H)/2N is, therefore, the frequency of A allele
in the population, and is represented by p
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Therefore, p = (2D + H) / 2N
or

p = (D + ½ H) / N and
q = (2R + H) / 2N or = (R + ½ H) / N

Therefore, p + q = 1 and p = 1 – q, or q = 1 – p

HARDY WEINBERG PRINCIPLE
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The value of p and q are known as gene frequencies
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In other words, the proportion of gametes carrying an allele, A or a, is known as gene frequency
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Random mating or random union of the two types of gametes would produce the following
genotypes in a ratio proportionate to the frequencies of the gametes that united to produce them
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▪ Disturbance in genetic equilibrium, or Hardy- Weinberg equilibrium, i
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, change of
frequency of alleles in a population would then be interpreted as resulting in evolution
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GENE MIGRATION
▪ When migration of a section of population to another place and population occurs, gene frequencies
change in the original as well as in the new population
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GENETIC DRIFT AND FOUNDER EFFECT

▪ There would be a gene flow if this gene migration, happens multiple times
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▪ Sometimes the change in allele frequency is so different in the new sample of
population that they become a different species
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NATURAL SELECTION
▪ Natural selection can lead to stabilisation (in which more individuals acquire mean
character value), directional change (more individuals acquire value other than the
mean character value) or disruption (more individuals acquire peripheral character
value at both ends of the distribution curve)



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