Describes about population genetics

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POPULATION GENETICS
1. Introduction
2. Terminologies
3. Hardy - Weinberg Law
4. Calculations
5. Factors affecting HWL

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Population is a group of individuals of the same species occupying a given
area that can freely interbreed and produce fertile offspring in nature
POPULATION

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The gene pool consists of all alleles at all gene loci in
all individuals of the population
Gene pool
Allele frequency
The percentage of an organism in a population that
carrying a particular allele

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Total number of allele in population
Allele frequency =
Number of specific type of allele
DOMINANT ALLELE?
Recessive allele?

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Total number of allele in population
Number of specific type of allele
Allele frequencies in a gene pool determine the genetic
change for a population
Composition of a gene pool may change over time due to
certain factors
If no change in allele frequencies from one generation
to the next, the gene pool is considered static
Genetic Equilibrium

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G. H. Hardy W. Weinberg

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Frequency of alleles and genotypes in a
population will remain constant from
generation to generation if the population is
stable and in genetic equilibrium
Five conditions
1. A large breeding population
2. Random mating
3. No mutation
4. No immigration or emigration
5. No natural selection
Hardy-Weinberg equilibrium (1908)

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 Organisms are diploid
 Only sexual reproduction occurs
 Generations are non overlapping
 Mating is random
 Population size is infinitely large
 Allele frequencies are equal in the sexes
 There is no migration, mutation or selection

10. Homozygous
Dominant
Homozygous
Recessive
Heterozygous

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Frequency of dominant allele (B) = p
Frequency of recessive allele (b) = q
B b

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BB Bb bb
(p + q)2 = p2 + 2pq + q2
p2 - Frequency of homozygous dominant
q2- Frequency of homozygous recessive
2pq - Frequency of heterozygous
BB
Bb
bb

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A plot of Hardy-Weinberg equilibrium genotype
frequencies as a function of allele frequencies

15. Calculation

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100 cats
84 black and 16 white
q2 = 16/100 = 0.16
q = √0.16 = 0.4
Frequency of each genotype?
p + q = 1
P + 0.4 = 1
p = 1 – 0.4
= 0.6

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p2 - Frequency of homozygous dominant = 0.6 × 0.6 = 0.36
q2- Frequency of homozygous recessive = 0.4 × 0.4 = 0.16
2pq - Frequency of heterozygous = 2 × 0.4 × 0.6 =0.48

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If it is three alleles
?p q r

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Factors affecting HWL
 Population size
 Type of mating
 Mutation
 Migration
 Natural selection

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Original population
Survivors
New population
Bottle Neck Effect

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