《医学遗传学》7年制课件Population Genetics.ppt

3.2．Selection 1.26 (malaria area) Sickle cell anemia (Aa) 0 Sickle cell anemia (aa) female 1.25 male 0.82 Huntington disease (Aa) female 0.75 male 0.41 Neurofibromatosis (Aa) 0.29 Hemophilia A (male) 0.2 Achondroplasia (Aa) 0 Retinoblastoma (Aa) 0 Tay-Sachs disease (aa) Fitness (f ) Genetic Disease 3.2．Selection Fitness (f ) One can survive and contribute to the gene pool of the succeeding generation. It is a measure of relative fertility. Selection coefficient (S ) means reducing fitness under the action of selection. Mutation pressure The continued production of an allele by mutation. 3.2．Selection Selection pressure The effectiveness of natural selection in altering the genetic composition of a population over a series of generations. 3.2．Selection Number of Deleterious Mutations 11 10 9 8 7 6 5 4 3 2 1 0 Mutation Selection Frequency Mutation will push the mean of this distribution up Selection will push the mean down. AD disease AR disease XR disease XD disease 3.2．Selection 3.2.1．Action of Selection 3.2．Selection 3.2.2．Increasing of Selection Pressure AD disease AR disease 3.2．Selection 3.2.2．Increasing of Selection Pressure 900230 90023 18005 9000 0.0001 0.001 90231 9023 1805 900 0.001 0.01 9240 924 185 90 0.01 0.10 1020 102 20 8 0.10 0.50 559 56 11 1 0.50 0.99 S=0.01 S=0.1 S=0.5 S=1 From q0 to qn Generation needed Change of q 3.2．Selection 3.2.2．Increasing of Selection Pressure AD disease AR disease XR disease 3.2．Selection 3.2.2．Decreasing of Selection Pressure AD disease AR disease XR disease Polymorphism 3.2．Selection The existence of two or more genetically different classes in the same interbreeding population. A polymorphic locus at which the rarer allele has a frequency more than 0.01. Balanced Polymorphism 3.2．Selection Genetic polymorphism maintained in a population because the heterozygotes for the alleles under consideration have a higher adaptive than either homozygote. 3.3．Random Genetic Drift Genetic drift is the random change in allele fre