II. Assumptions of H-W equilibriumLecture 6 BIO 311D 2nd EditionOutline of Last Lecture I. Linked genesII. Mechanisms of sex determination III. XX mammals are genetic mosaicsIV. Intro to population geneticsOutline of Current Lecture I. Hardy Weinberg population equationsII. Assumptions of H-W equilibriumIII. How can microevolution happen?Current LectureI. Hardy Weinberg population equationsA. The equation is a quantitative expression relating allele frequency and genotype frequencyB. Normal sexual reproduction (normal meiosis and random fertilization) results in the same allele and genotype frequencies in the next generation, thus “Hardy- Weinberg equilibrium” C. Practice Problems1. 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? p2 =.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. Assumptions of H-W equilibriumA. Large population size, so less effect of chance eventsB. No gene flow into/out of a population or between populations C. Mutations not significant D. Random matingE. No natural selectionIII. 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 populationC. Genetic drift: changes in gene frequencies caused by stochastic factors (usually chance fate/use of particular gametes) operates most strongly in small
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