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01:119:115 (825)
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Lecture

# Ch. 19

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School
Department
Biological Sciences
Course
01:119:115
Professor
D'arville
Semester
Spring

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Ch. 19 Evolution 2 -- Population Genetics & Microevolution 4 / 5 / 12 Evolution is a process of adaptation to the environment. Natural selection acting on variation (preserving if beneficial, removing if detrimental) is the means by which this adaptation occurs How do populations evolve?? • Variation is the ‘raw material’ for selection ← Scales of evolution • Microevolution: short-term, small-scale changes, below species level populations; result of a change in gene frequency • Macroevolution: long-term, large-scale changes above the species level ← Population: all individuals of the same species in a particular area at the same time. Share a common gene pool Gene pool: sum of all alleles of all genes in a population Genetics: way to measure evolution Frequency of genotypes and alleles are stable --> genetic equilibrium Frequency changes --> evolution Allele frequency: heterozygous crossing Ex: A = 0.9 a = 0.1.....AxA= P^2 = 0.81 Hardy-Weinberg equation: • Describes a population in equilibrium (not evolving) • Predicts changes in offspring gene frequencies (permits tracking changes from generation- to-generation) • Says gene frequencies don’t change by themselves • Describes an idealized population that is not evolving (i.e. Genetic equilibrium) • That is, under certain conditions, populations allele frequencies are in genetic equilibrium • 5 conditions necessary for H-W equilibrium: 1. No mutations 2. No migration 3. Large population size (i.e. No genetic drift) 4. Random mating: 5. No natural selection Equation: Q^2 = frequency of aa 2pq = frequency of Aa 1 = all the individuals in a population Ex: how many people are ‘carriers’ for albinism? 2pq, albinism is recessive (q), 1 in 20.000 are albinos (q^2) If q^2 = 1/20,000, then q = 1/141 Ex: what proportion of mouse population will have white coats if: P = 0.8 Q = 0.2 0.64 + 2(0.16) + 0.04 = 1 Random mating Offspring genotypes AA: 25% Aa: 50% aa 25% Non-random mating Offspring genotypes AA: 42% Aa: 17% Aa42% P^2 + 2pq + q^2 = 1 The 5 microevolutionary processes that cause departures from H-W equilibrium: i. Mutation: c
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