Population Genetics Bio 135 Summer 2009 metabolize the amino acid phenylalanine to the amino acid tyrosinephenylalaninetyrosinemetabolize the amino acid.

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Presentation transcript:

Population Genetics Bio 135 Summer 2009 metabolize the amino acid phenylalanine to the amino acid tyrosinephenylalaninetyrosinemetabolize the amino acid phenylalanine to the amino acid tyrosinephenylalaninetyrosinemetabolize the amino acid phenylalanine to the amino acid tyrosinephenylalaninetyrosine

Population Genetics The study of gene distribution in population How gene frequencies or genotypes are maintained or changed Concerns both genetic factors (mutation and mating) and environmental factor (selection and migration)

What happens with a mutant gene? Existing in decreased number until disappearance- why? Existing in increased number- why? Existing in stable number- why?

Gene frequency in a Population Is a balance between new mutation rate, fitness, selection and other factors

Gene frequencies vary among different ethnic groups 1. Europian / US Caucasian: cystic fibrosis, 2. French Canadian: PKU- metabolize the amino acid phenyalanine to the amino acid tyrosine 3. Ashkenazi Jews: Tay-Sachs- build up of lipid in nerve cells in the brain 4. African: sickle cell anemia- blood disorder 5. Asian:  and β thalassemia- blood disorder

Hardy-Weinberg Law Use in calculating genotype frequency from phenotype data- assumes only 2 alleles in a population p = frequency of dominant allele: A q = frequency of recessive allele: a p+q = 1

Hardy-Weinberg Law Frequency of genotype AA = p 2 Frequency of genotype aa = q 2 Frequency of genotype Aa = 2pq Sum of all genotype = p 2 + 2pq + q 2 = (p+q) 2 = 1

Proportion of each genotype (AA:Aa:aa) will remain constant at equilibrium if allele frequencies remain constant Hardy-Weinberg Law

Factors that disturb Hardy- Weinberg equilibrium (1) No mutations- no new alleles No migration into/out of the population Random mating- all individuals have an equal chance of reproducing Large population- no random chance of shifting allele frequency No Natural Selection occurs

Some of the Five H-W factors always occur Be able to explain why we use H-W equilibrium Hardy-Weinberg equilibrium

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