hardy Weinberg law

2. HARDY WEINBERG LAW – FACTORS AFFECTING
EQUILIBRIUM
FREQUENCIES IN RANDOM MATING POPULATIONS
PREPARED BY....
KIRAN DASANAL
[UG13AGR1879]
The
Hardy-Weinberg
Equilibrium
Allele Frequencies in a
Population
G.H. Hardy
English Mathematician
Dr. Wilhelm Weinberg
German Physician

3. INTRODUCTION
• Cross-pollinated crops are highly heterozygous
due to the free intermating among their
plants. They are often referred to as random
mating populations.
• Mendelian population
• A population, in this case, consists of all such
individuals that share the same gene pool

4. Hardy-Weinberg law
• The Hardy-Weinberg law is the fundamental
law of population genetics and provides the
basis for studying Mendelian populations.
• This law was independently developed by
Hardy (1908) in England and Weinberg (1909)
in Germany.

5. Hardy-Weinberg law

The Hardy-Weinberg law states that the gene
and genotype frequencies in a Mendelian
population remain constant generation after
generation if there is no selection, mutation,
migration or random drift.

8. Example of Hardy-Weinberg law
• Let us consider a single gene with two alleles,
A and a, in a random mating population.
• There would be three genotypes, AA, Aa and
aa, for this gene in the population.
• Suppose the population has N individuals of
which D individuals are AA, H individuals are
Aa and R individuals are aa.
• so that D +H + R = N.

9. Cont…………
• p = (2D + H) / 2N or
= (D + ½ H) / N and
• q = (2R + H) / 2N or
= (R + ½ H) / N
• Therefore, p + q = 1
• 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. This equilibrium is known as Hardy-
Weinberg equilibrium.

11. Factors affecting equilibrium
frequencies

12. Migration
• Migration is the movement of individuals into
a population from a different population.
• Migration may introduce new alleles into the
population or may change the frequencies of
existing alleles.
• In plant breeding programmes, migration is
represented by intervarietal crosses,
polycrosses, etc., wherein the breeder brings
together into a single population two or more
separate populations.

13. Mutation
• Mutation is a sudden and heritable change in
an organism and is generally due to structural
change in a gene.
• It is the ultimate source of all the variation
present in biological materials.
• Mutation may produce a new allele not
present in the population or may change the
frequencies of existing alleles.

14. Random drift
• Random drift or genetic drift is a random
change in gene frequency due to sampling
error.
• Random drift occurs in small populations
because sampling error is greater in a smaller
population than in a larger one.
• The breeder cannot do anything to prevent
this genetic drift, except to use very large
populations.

15. Inbreeding
• Mating between individuals sharing a
common parent in their ancestry is known as
inbreeding.
• Inbreeding reduces the proportion of
heterozygotes or heterozygosity and increases
the frequency of homozygotes or
Homozygosity.

16. Selection
• Differential reproduction rates of various
genetypes is known as selection.
• The breeder is able to improve the various
characteristics by selecting for the desirable
types. In a random mating population.
• selection is expected to change gene
frequencies rather than to eliminate one or
the other allele.

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