Lecture 6 BIO 311D 2nd Edition Outline of Last Lecture I Linked genes II Mechanisms of sex determination III XX mammals are genetic mosaics IV Intro to population genetics Outline of Current Lecture I Hardy Weinberg population equations II Assumptions of H W equilibrium III How can microevolution happen Current Lecture I Hardy Weinberg population equations A B C The equation is a quantitative expression relating allele frequency and genotype frequency Normal sexual reproduction normal meiosis and random fertilization results in the same allele and genotype frequencies in the next generation thus Hardy Weinberg equilibrium Practice Problems 1 If the alleles for a certain trait single locus simple dominance had frequencies of p 0 7 and q 0 3 then a what is the frequency of homozygous dominant individuals p 2 49 b What is the frequency of heterozygous individuals 2pq 42 c If this trait phenotype was determined for 100 individuals randomly chosen from the population how many would show the recessive trait 9 2 Within a population of butterflies the color brown B is dominant over the color white b and 25 of all butterflies are white Given this simple information calculate the following a the percentage of butterflies in the population that are heterozygous and b the percentage of homozygous dominant individuals P2 25 2pq 50 3 In a population of mice 4 0 04 of the individuals are albino phenotype showing simple recessive trait so their genotype is aa and the rest are all agouti brown phenotype showing the dominant trait A a what is the frequency of the white allele a 2 of the agouti allele A 8 allele frequency b what proportion of the mice are heterozygotes Aa 32 genotype frequency c what proportion of the mice are homozygous dominant 64 genotype frequency d In a sample of 50 mice taken from this population how many mice would be expected to show the dominant trait 32 number of individuals showing A trait II A B C D Assumptions of H W equilibrium Large population size so less effect of chance events No gene flow into out of a population or between populations Mutations not significant Random mating E III No natural selection How can microevolution happen A When the H W assumptions aren t met microevolution occurs B Non random mating Assortative mating either positive or negative is non random Sexual selection adds to non random mating Extreme case is inbreeding causes an increases the percentage of homozygous recessive genotype in a population C Genetic drift changes in gene frequencies caused by stochastic factors usually chance fate use of particular gametes operates most strongly in small populations
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