Hardy-Weinberg Principle
Factors Affecting Allele Frequency
Mutation Rate
Migration and Isolation
Population Size
Natural Selection
Environmental Change
Genetic Drift
Gene Flow
Non-random Mating
Hardy-Weinberg Principle
Assumptions:
o Population is large enough to make sampling error negligible
o Mating in the population is random
o No selective pressures for or against any genotype so no selection
o No mutation, migration or genetic drift
Frequency of dominant allele = p
Frequency of recessive allele = q
Only two alleles in population so p + q = 100% or 1.0
Possible allele combinations:
o Homozygous Dominant: pp = p²
o Homozygous Recessive: qq = q²
o Heterozygous x2: pq x2 = 2pq
p² + 2pq + q² = 100% or 1.0
Examples:
25% population recessive trait, 75% 36% population recessive trait, 64%
dominant trait dominant trait
q² = 0.25 so q=0.5 q² = 0.36 so q=0.6
1.0 – 0.5 = p = 0.5 1.0 – 0.6 = p = 0.4
2pq = 2x0.5x0.5 = 0.5 2pq = 2x0.4x0.6 = 0.48
So 50% of the population are So 48% of the population are
heterozygous heterozygous
Factors Affecting Allele Frequency
Mutation Rate
Migration and Isolation
Population Size
Natural Selection
Environmental Change
Genetic Drift
Gene Flow
Non-random Mating
Hardy-Weinberg Principle
Assumptions:
o Population is large enough to make sampling error negligible
o Mating in the population is random
o No selective pressures for or against any genotype so no selection
o No mutation, migration or genetic drift
Frequency of dominant allele = p
Frequency of recessive allele = q
Only two alleles in population so p + q = 100% or 1.0
Possible allele combinations:
o Homozygous Dominant: pp = p²
o Homozygous Recessive: qq = q²
o Heterozygous x2: pq x2 = 2pq
p² + 2pq + q² = 100% or 1.0
Examples:
25% population recessive trait, 75% 36% population recessive trait, 64%
dominant trait dominant trait
q² = 0.25 so q=0.5 q² = 0.36 so q=0.6
1.0 – 0.5 = p = 0.5 1.0 – 0.6 = p = 0.4
2pq = 2x0.5x0.5 = 0.5 2pq = 2x0.4x0.6 = 0.48
So 50% of the population are So 48% of the population are
heterozygous heterozygous
