Population Genetics Its importance Its predictive value Ch 23

Population? Define - Group of interbreeding organisms (a species) - Reside within a specified geographic region Example: Humans in the Pacific northwest Grey whales in Puget Sound Genetically related Gene pool =all the alleles within the population

Gene frequency in a population p= frequency of dominant allele or f(dominant allele) q= frequency of recessive allele or f(recessive allele) 1= p+ q If p=0.3, then q=1-0.3=0.7

The frequency of every possible combination of a given pair of alleles in a population can be determined mathematically with: 1=(p+q)(p+q) Expand: 1=p 2 + 2pq +q 2 F(homozygous dominants) F(heterozygotes) F(homozygous recessives)

If the frequency of cystic fibrosis, a recessive allele, is 0.4 in Europe, 1. what is the frequency of the normal allele? 2. What is the frequency of people with the disease? 3.What is the frequency of carriers? 4.If the population size is 20,000, how many people have the disease? Want to solve for p p=1-0.4= 0.6 Want to solve for q2 q 2 =0.4 2 =0.16 Want to solve for 2pq 2pq=2(0.4)(0.6)=0.48 q 2 (20,000)=3,200

Genotype of population-->phenotype Some phenotypes adaptive (advantageous)--> increased fitness (fertility) Some:neutral --> fitness unchanged Others: negative --> decrease fitness Consider: frogs adaptive traits neutral negative Ability to leap away from predators Color of toenails Inability to live in arid environment

Genetic change--> phenotypic change-->impacts fitness Changes in a population’s gene pool --> changes in gene frequency in a population Evolutionary ecologists take all these factors into account. Focus on: Microevolution

Hardy-Weinberg equilibrium 1=p 2 + 2pq +q 2 1= p+ q Assumes: no change over time; no evolution from one generation to the next Equilibrium Conditions 1. No DNA mutation 2. No natural selection 3. No migration (no gene flow between populations) 4. Random mating 5. Large population

Hardy and Weinberg must be joking! A static environment; no change! I would question that. When changes in allele frequencies occur, how does one determine the cause? What significance does it have if any?