These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Lecture 39 Outline of Last Lecture I. Population genetics a. Composition of population genetics b. Gene pool II. Populations a. Characteristics b. Demes III. Allele and gene frequencies a. Polymorphism b. Single-nucleotide polymorphism c. Allele frequency i. Equation ii. Example d. Genotype frequency i. Equation ii. Example e. Trends in frequencies f. Hardy-Weinberg equilibrium i. Conditions ii. Equation iii. Example g. X2 test i. Equation ii. Example iii. Results IV. Patterns of evolution a. Microevolution b. Natural selection c. Genetic drift i. Bottleneck effect ii. Founder effect d. Migration e. Non-random mating i. Assortative mating ii. Positive assortative mating iii. Negative assortative mating iv. Inbreeding v. Outbreeding GCD 3022 1st editionf. Sources of new genetic variation i. Mutations ii. Exon shuffling iii. Horizontal gene transfer iv. Changes in repetitive sequences g. DNA fingerprinting Outline of Current Lecture I. Genetic drift a. Population size b. Bottleneck effect II. Hardy-Weinberg Equilibrium a. PTC Example b. Tongue Rolling Example c. Sheep Example III. Inbreeding a. Allele and genotype frequencies b. Rare recessive genetic diseases Current Lecture I. Genetic drift: the effect that causes allele fixation or loss in a small population over many generations. Can be due to events such as natural disasters, bottleneck effect, or founders effect. Due largely in part to random sampling error that occurs in small populations. a. Population size: this effect is more likely to occur in small populations than large because there are less alleles in the gene pool which results in a greater “ripple” when a random event occurs to the population. In other words, it is much easier to decrease the genetic variation in a small population than a large one because the small population already has limited genetic variation. b. Bottleneck effect: occurs when a random catastrophic event occurs to a population which greatly reduces genetic variability (at random). This can result in the loss of alleles from the population and the individuals who survive the bottleneck event will reproduce, resulting in much less genetic variation in the future generations. II. Hardy-Weinberg Equilibrium: the equation that predicts the frequency of alleles and genotypes in a population assuming that there are no mutations, no genetic drift, no migration, no natural selection, and random mating. a. PTC Example: the ability to taste PTC is an autosomal dominant trait (inability to taste PTC is recessive). In a sample of 500 people, 360 have the ability to taste PTC and 140 do not. i. The recessive allele (q): 140/500 = 0.28 = q2 (0.28)2 = q = .53 ii. The dominant allele (p): 1-0.53 = 0.47 = p (0.47)2 + 2(0.47)(0.53) = 0.72iii. Each genotype: pp = (0.53)2 = 0.28 Pp = [2(0.47)(0.53)] = 0.50 PP = (0.47)2 = 0.22 b. Tongue Rolling Example: the ability to roll your tongue is inherited as a recessive trait. Frequency of tongue rolling allele is 0.6 and the nonrolling allele is 0.4. q = 0.6, p =0.4 p2 + 2pq + q2 = 1 (0.4)2 + 2(0.4)(0.6) + q2 = 1 q2 = 0.36 (frequency of people who can roll their tongues) c. Sheep Example: in a large herd of 5468 sheep, 76 animals have yellow fat, and the rest have white fat. Yellow fat is inherited as a recessive trait. The herd is assumed to be in Hardy-Weinberg equilibrium. i. Frequencies of white and yellow fat alleles in the population 76/5468 = 0.014 = q2 0.118 = q (yellow alleles) 1-.118 = 0.882 = p (white alleles) ii. Number of sheep that are heterozygous (carry yellow allele) 2(p)(q) = 2(0.882)(0.118) = (0.208)(5468) = 1138 sheep III. Inbreeding: mating between related individuals (non-assortative mating) a. Allele and genotype frequencies: allele frequency is not affected by inbreeding because inbreeding does not favor one allele over the other. Genotype frequency is affected though because homozygosity is favored overall. b. Rare recessive genetic diseases: the reason that rare genetic recessive diseases are more common in inbred populations is the favoring of homozygosity in these populations. Overall, there will be more homozygous recessive individuals in the population than an outbred
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