Anthro Lecture 2-26

Anthro Lecture 2-26 - Anthro Lecture 2-26 I Genetics a...

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Anthro Lecture 2-26 I. Genetics a. Genetic data provide important clues about modern human origins b. Brief primer i. Plant and animal cells carry mitochondria ii. Mitochondria regulate energy processing in cells iii. Mitochondria contain small amounts of DNA (mtDNA c. mtDNA is useful for reconstructing evolutionary events i. Inherited only through maternal line 1. No recombination 2. All change is product of mutation ii. Mutation rate is high 1. Change accumulates fairly rapidly 2. Provides information about fairly recent branching events iii. More copies present in cells, compared to nuclear DNA d. We can measure the amount of genetic variation within and between populations i. Remember that DNA consists of two long backbones of alternating sugar and phosphate molecules e. Compute amount of genetic diversity among individuals i. Extract mtDNA from large number of individuals ii. Sequence their mtDNA iii. Characterize same parts of mtDNA sequence for all individuals iv. Compare all pairs in sample at each nucleotide (base pair) v. Compute average number of differences per base pair between individuals vi. Number of differences = amount of genetic diversity
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We can compute variation within and between populations i. Consider 3 chimpanzee subspecies 1. East Africa, Central Africa, West Africa 2. There is generally more variation between populations than within them ii. Now compare the amount of genetic variation among humans from Africa, Asia, and Europe 1. Humans are much less variable than any of the chimp populations a. There is more variation within populations than between them iii. Two humans from the same population are more similar than 2 chimps from the same population iv. Two humans from different populations are more similar than two chimps from same population v. Compared to all the other Great Apes, humans show very little genetic variation II. Why are humans less variable than chimpanzees? a. Think back to genetic drift b. Mutation introduces variation at low rate c. Genetic drift eliminates variations i. Rate of loss depends on population size ii. Big populations are more variable than small populations d. At mutation-drift equilibrium, m = 2Nu i. M = amount of variation ii. U = mutation rate iii. N = population size e. If we use known values of variation and mutation rates, we can estimate the expected size of the modern human population
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Anthro Lecture 2-26 - Anthro Lecture 2-26 I Genetics a...

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