Population Genetics

Population Genetics

1. In a population there are many different phenotypes, proteins, and alleles (DNA)

2. Allele frequencies vary from population to population

   • Africans have a high frequency of the sickle cell allele, Northern Europeans have a high frequency of the cystic fibrosis allele, Ashkenazi Jews have a high frequency of the Tay Sachs allele

3. Hardy-Weinberg Law

   • Frequencies of alleles of the same gene will remain the same from generation to generation provided: that population is infinitely large, mating is random, selection is not occurring, no mutation , no migration
   • Problem: populations vary in size
     • Genetic Drift
       • Random changes in gene frequencies due to chance; seen in small populations
       • Causes
         • Size is small over a long period of time
         • Founder Effect
         • Bottleneck Effect
           • Genetic bottleneck: some genotypes do not survive
   • Problem: there are many situations where mating is not random
     • Positive Assortative mating, Negative Assortative mating
   • Problem: inbreeding
     • Preferential mating between close relatives. Often a necessity if the population is small
   • Problem: Endogamy
     • Marrying within a group