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1、群体遗传学基础和重测序分析,王理中,Population genetics,genetic structure of a population,genetic structure of a population,group of individuals of the same species that can interbreed,Population genetics,Population genetics,genetic structure of a population,group of individuals of the same species that can interbree
2、d,alleles genotypes,Total= 200 fishes,Genotype and Allele Frequencies,describes a mathematical relationship between allele frequencies and genotype frequencies:,The Hardy-Weinberg Principle,The Hardy-Weinberg Principle Feature 1,Allele frequencies in a population will not change, generation after ge
3、neration. The population is sufficiently large Mating is random Allele frequencies are the same in males and females Selection does not occur (all genotypes have equal in viability and fertility) Mutation and migration are absent,No selection, mutation, drift, migration, non-random mating,The Hardy-
4、Weinberg Principle Feature 2,Another important implication is that for a rare allele, there are many more heterozygotes than there are homozygotes for the rare allele,Testing for H-W Equilibrium Example 1,Only one of the populations below is in genetic equilibrium. Which one?,Only one of the populat
5、ions below is in genetic equilibrium. Which one?,Testing for H-W Equilibrium Example 1,Only one of the populations below is in genetic equilibrium. Which one?,Testing for H-W Equilibrium Example 1,Data: 26 MM, 68 MN, 106 NN, with a total population of 200 individuals. 1. Observed genotype frequencie
6、s: MM: 26/200 = 0.13 MN: 68/200 = 0.34 NN: 106/200 = 0.53 2. Allele frequencies: M: 0.13 + 1/2 * 0.34 = 0.30 N: 0.53 + 1/2 * 0.34 = 0.70 3. Expected genotype frequencies and numbers: MM: p2 = (0.30)2 = 0.09 (freq) x 200 = 18 MN: 2pq = 2 * 0.3 * 0.7 = 0.42 (freq) * 200 = 84 NN: q2 = (0.70)2 = 0.49 (f
7、req) * 200 = 98 4. Chi-square value: (26 - 18)2 / 18 + (68 - 84)2 / 84 + (106 - 98)2 / 98 = 3.56 + 3.05 + 0.65 = 7.26 5. Conclusion: The critical chi-square value for 1 degree of freedom is 3.841. Since 7.26 is greater than this, we reject the null hypothesis that the population is in Hardy-Weinberg
8、 equilibrium.,Testing for H-W Equilibrium Example 2,Population genetics,genetic structure of a population,group of individuals of the same species that can interbreed,alleles genotypes,Patterns of genetic variation in populations Changes in genetic structure through time,Genetic variations,Genetic v
9、ariations,variation,no variation,adaptation to environmental change,Why is genetic variation important?,Why is genetic variation important?,variation,no variation,divergence of populations,Why is genetic variation important?,variation,no variation,divergence of populations,divergence,NO DIVERGENCE!,
10、Ps = S/n,w = Ps / a1,Polymorphism (SNPs),changes in allele frequencies and/or genotype frequencies through time,How does genetic structure change?,mutation migration natural selection genetic drift non-random mating,How does genetic structure change?,changes in allele frequencies and/or genotype fre
11、quencies through time,mutation migration natural selection genetic drift non-random mating,How does genetic structure change?,How does genetic structure change?,mutation migration natural selection genetic drift non-random mating,“gene flow”,migration,HH,hh,h,H,differences in survival or reproductio
12、n,certain genotypes produce more offspring,leads to adaptation,How does genetic structure change?,mutation migration natural selection genetic drift non-random mating,Natural selection,Directional selection (positive selection) Stabilizing selection (negative selection) Disruptive selection (diversi
13、fying selection),Resistance to antibacterial soap,Natural selection,Generation 1: 1.00 not resistant 0.00 resistant,Natural selection,Resistance to antibacterial soap,Generation 1: 1.00 not resistant 0.00 resistant,Natural selection,Resistance to antibacterial soap,mutation!,Generation 1: 1.00 not r
14、esistant 0.00 resistant,Generation 2: 0.96 not resistant 0.04 resistant,Natural selection,Resistance to antibacterial soap,Generation 1: 1.00 not resistant 0.00 resistant,Generation 2: 0.96 not resistant 0.04 resistant,Generation 3: 0.76 not resistant 0.24 resistant,Natural selection,Resistance to a
15、ntibacterial soap,Generation 1: 1.00 not resistant 0.00 resistant,Generation 2: 0.96 not resistant 0.04 resistant,Generation 3: 0.76 not resistant 0.24 resistant,Generation 4: 0.12 not resistant 0.88 resistant,Natural selection can cause populations to diverge,divergence,Selection favors heterozygot
16、es (Aa) Both alleles maintained in population (a at low level),a,A,Selection on sickle-cell allele,How does genetic structure change?,mutation migration natural selection genetic drift non-random mating,Genetic drift,8 RR 8 rr,Before:,After:,2 RR 6 rr,Genetic drift - Bottleneck Effect,a drastic reduction in population (volcanoes, earthquakes, landslides ) Reduced genetic variation Smaller population may not
