Population genetics and Hardy-Weinberg Section 27.3 – Nov 18, 2014

Population genetics Individuals CANNOT evolve – evolution happens at population level Genetic changes occur within a population over generations = phenotypic changes Microevolution – change in gene frequencies within a population over time

Population genetics  Population – all members of a single species that occupy a certain area and breed together Example of two different populations?? Gene pool – (following Mendel’s laws) the total number of alleles at all the gene loci in all members (that are capable of sexual reproduction)

Hardy-Weinberg Equilibrium p2 + 2pq + q2 = 1 p2 = frequency of DD genotype (homozygous dominant) 2pq = frequency of Dd genotype (heterozygous) q2 = frequency of dd genotype (homozygous recessive)

Hardy-Weinberg Equilibrium Example: Uses Punnett squares to determine genotype frequencies

Hardy-Weinberg Equilibrium “allele frequencies in a gene pool will remain at equilibrium, and thus constant after one generation of random mating in a large, sexually reproducing population as long as five conditions are met” No mutations No genetic drift No gene flow Random mating No selection Why is it that in real life these conditions are almost NEVER met?

Hardy-Weinberg Equilibrium Hardy-Weinberg equilibrium states that allele frequencies in a gene pool within a population do not change If they do change = microevolution Use Hardy-Weinberg to detect deviations from equilibrium Deviations suggest that one or more of the five conditions is occurring

Example: Moths

Example In some areas of Africa, the recessive sickle-cell allele has a frequency of 0.3. The frequency of the normal hemoglobin allele is calculated as: 1-0.3 = 0.7 0.72 = 0.49 =SS 2(0.7)(0.3) =0.42 = Ss (42% of the population) 0.32 = 0.09 = ss (9% of the population affected by sickle-cell anemia) 0.49 + 0.42 + 0.09 = 1 p p2 2pq q2

Complete “Check Your Progress” pg. 552 #1-2 Handouts Hardy-Weinberg explained by Yogi Bear Hardy-Weinberg Problems

Some people think that the dominant allele of a gene should constantly increase in frequency in a population, and quickly force out the recessive allele. Use the Hardy-Weinberg principle and/or equation to explain why this idea is incorrect. What false assumptions could cause people to have this incorrect idea?