Transcript 11/29 Population Genetics

25.1 Genotypic and Allelic Frequencies Are
Used to Describe the Gene Pool Of a
Population
• Calculating genotypic frequencies
• F = No.AA individuals/N
• N: total no. of individuals
• F: frequency of AA alleles.
• Calculating allelic frequencies
• Frquency of an allele = No. copies of the
alleles/No. copies of all alleles at the locus in
a population.
25.2 The Hardy-Winberg Law Describes the
Effect of Reproduction on Genotypic and
Allelic Frequencies
• Hardy-Weinberg Law
• Assumption: population is large, randomly
mating, not affected by mutation, migration, or
natural selection.
• Prediction 1: the allelic frequencies of a
population do not change.
• Prediction 2: the genotypic frquencies
stabilize.
Genotypic frequencies at H-W equilibrium
• p+q=1
• p2 + 2pg + q2 = 1
• P2: homozygous dominant allele pair frequency.
• Q2 :homozygous recessive allele pair frequency.
• 2pq: heterozygous allele frequency.
Concept Check 1
What is the expected frequency of heterozygotes
in a population with allelic frequency X and Y that
is in H-W?
a.
b.
c.
d.
X+Y
XY
2XY
(X- Y)2
Concept Check 1
What is the expected frequency of heterozygotes
in a population with allelic frequency X and Y that
is in H-W?
a.
b.
c.
d.
X+Y
XY
2XY
(X- Y)2
25.3 Nonrandom Mating Affects the Genotypic
Frequencies of a Population
• Positive assortative mating:
• a tendency of like individuals to mate.
• Negative assortative mating:
• A tendency of unlike individuals to mate.
Inbreeding
• Increases frequency of homozygotes in
population
• Rate is affected by how closely related
mating pairs are
Concept Check 2
What is the effect of outcrossing on a population?
a.
b.
c.
d.
Allelic frequency changes in the population.
More heterozygotes will be produced in the population.
Fewer heterozygotes will be produced.
It will reach the H-W equilibrium
Concept Check 2
What is the effect of outcrossing on a population?
a.
b.
c.
d.
Allelic frequency changes in the population.
More heterozygotes will be produced in the population.
Fewer heterozygotes will be produced.
It will reach the H-W equilibrium
25.4 Several Evolutionary Forces Potentially
Cause Changes in Allelic Frequencies
• Mutation
• Migration
• Genetic Drift
• Founder effect
• Genetic bottle neck
• Natural selection