Basic concepts of population genetics - Bioversity International

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Consequences of a decreasing population size Genetic drift, with random variation of allele frequencies Inbreeding Homozygosity: fixation and loss of alleles Subpopulation differentiation AA aa AA AA AA aa aa aa AA Aa AA Aa Aa aa aa Aa AA aa aa Aa Aa Aa AA AA aa Aa Aa Aa Aa Population size is reduced AA AA aa AA Aa AA Aa Mating among relatives aa AA Copyright: IPGRI and Cornell University, 2003 Population genetics 40 Events that reduce population size: Domestication 40 aa aa aa aa AA aa aa Aa AA AA Aa AA AA AA aa Homozygosity increased Subpopulations (inbreeding, clonal reproduction) Long-range dispersal (founder effect) Regeneration of genetic resources collections aa aa aa aa aa aa aa aa aa AA AA AA AA AA AA AA AA AA Population differentiation Fixation (continued on next slide)
Consequences … (continued) A bottleneck develops when the population size drops sharply The founder effect occurs when a few individuals colonize and become established in a new environment p = 0.5 (frequency of A 1 ) q = 0.5 (frequency of A 2 ) N A1A1 A1A1 A1A2 A1A1 A1A1 A1A2 A1A1 A2A2 A2A2 A2A2 A2A2 A1A2 A2A2 A1A1 A2A2 A2A2 A1A2 A1A1 A1A2 A1A2 A1A1 A1A2 A1A2 A2A2 A 2 A 2 Bottleneck Copyright: IPGRI and Cornell University, 2003 Population genetics 41 41 A 2 A 2 p = 0.0 (frequency of A 1 ) q = 1.0 (frequency of A 2 ) A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 A2A2 Small populations are highly vulnerable to extinction because the surviving sample may not be representative of the pre-crash genepool. Both effects depend on the number of survivors (or colonizers) and the rate of population growth. The graphic in the slide shows a bottleneck effect. To the left is a population in Hardy-Weinberg equilibrium with allele frequencies of 0.5. If a sudden reduction occurs, then the original size restored, the result may be a loss of alleles and the fixation of others. In the example (right), only A 2 A 2 survived and allele A 1 was lost. time
Page 1 and 2: Genetic diversity analysis with mol
Page 3 and 4: Definitions: Population genetics T
Page 5 and 6: Phenotypic variation Pink Pale crea
Page 7 and 8: Genotype is … The description of
Page 9 and 10: What is polymorphism? ‘Presence
Page 11 and 12: Population structure Three levels o
Page 13 and 14: Allele frequency Allele frequency
Page 15 and 16: Genotype frequency This is the fre
Page 17 and 18: Demonstrating the H-W principle Gen
Page 19 and 20: The chi-square test This hypothesi
Page 21 and 22: Calculating allele frequencies: Exa
Page 23 and 24: Locus A B D … with a codominant m
Page 25 and 26: Locus A Locus B Locus D … with a
Page 27 and 28: ... with a codominant gene having m
Page 29 and 30: Random mating Mating that takes pl
Page 31 and 32: Inbreeding coefficient It compares
Page 33 and 34: Forces shaping genetic diversity M
Page 35 and 36: Migration It is the movement of in
Page 37 and 38: Selection It is the inherited abili
Page 39: Effective population size Ne is th
Page 43 and 44: Appendix 1 Copyright: IPGRI and Cor
Page 45 and 46: By now you should know … The bas
Page 47:
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