Hardy-Weinberg Law: Comparing Genotypic exp with freq
1. Calculate the allelic frequencies
2. Find the expected genotypic frequencies
3. Compare the observed and expected genotypic frequencies using a chi-square test
How do you calculate the degrees of freedom for the Chi-Square test in Hardy-Weinberg proportions?
In general, the degrees of freedom for a chi-square test of Hardy-Weinberg equilibrium equal the number of expected genotypic classes minus the number of associated alleles
Positive assortative mating
Tendency for individuals sharing a particular trait to mate
Negative assortative mating
Tendency for individuals that do not share a particular trait to mate
Inbreeding
Preferential mating between related individuals
Outcrossing
Avoidance of mating between related individuals
How does inbreeding affect homozygosity and allele frequencies?
Inbreeding leads to an increase in homozygosity at all loci, but no change in allele frequencies
Inbreeding depression
The increased appearance of lethal and deleterious traits with inbreeding
Processes that bring about change in allelic frequency
Mutation
Migration
Genetic Drift
Natural selection
Genetic Drift
Sampling error/random effects due to small population size
What are the overall affects of migration?
Gene pools of populations become more similar
Increases genetic variation within the recipient population
Genetic drift results in...
the divergence of populations and often results in one allele becoming fixed
What are two causes of genetic drift?
Founder Effect
Genetic bottleneck
Three related effects of genetic drift are:
1. Change in allelic frequency
2. Reduced genetic variation
3. Different populations diverge genetically with time
Natural Selection
The differential reproduction of genotypes when individuals with adaptive traits produce a greater number of offspring than that produced by others in the population
Fitness
The reproductive success of one genotype compared with the reproductive successes of other genotypes in the population
Calculating fitness (W)
Divide the mean number of offspring produced by a genotype by the mean number produced by the most proliﬁc genotype
Selection coefﬁcient (s)
The relative intensity of selection against a genotype
Calculating the selection coefﬁcient
s = 1 - W
General Selection Model
know table 25.4
Three Different types of selection
Selection against a dominant allele is very efﬁcient
Selection against an autosomal recessive allele is inefﬁcient
Balancing selection where the heterozygous genotype is most ﬁt
Do problem on slide 21
calculate relative fitness and next generation frequency of an allele
Mutation's long-term effect on allelic frequency
Equilibrium reached between forward and reverse mutations
Migration's long-term effect on allelic frequency
Equilibrium reached when allelic frequencies of source and recipient population are equal
Genetic drift's long-term effect on allelic frequency
Fixation of one allele
Natural Selection's long-term effect on allelic frequency