# Bio115-lecture36

 Hardy-Weinberg Law: Comparing Genotypic exp with freq 1. Calculate the allelic frequencies2. Find the expected genotypic frequencies3. 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 MutationMigrationGenetic DriftNatural 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 similarIncreases 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 EffectGenetic bottleneck Three related effects of genetic drift are: 1. Change in allelic frequency2. Reduced genetic variation3. 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 efﬁcientSelection against an autosomal recessive allele is inefﬁcientBalancing 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 Directional selection: fixation of one alleleOverdominant selection: equilibrium reached Authorlukemlj ID52039 Card SetBio115-lecture36 DescriptionBio115 lecture 36 Updated2010-11-28T21:57:29Z Show Answers