Population Genetics

1. Population Genetics • Population-all the members of a single species that occupy a particular region • Population genetics-studies the genetic diversity of a population • Single nucleotide polymorphisms (SNPs)-variation in DNA sequence at a single nucleotide, important in human diversity • Haplotypes: haplotype is a set of single-nucleotide polymorphisms (SNPs) on a single chromatid that are statistically associated. It is thought that these associations, and the identification of a few alleles of a haplotype block, can unambiguously identify all other polymorphic sites in its region. Such information is very valuable for investigating the genetics behind common diseases, and has been investigated in the human species by the International HapMap Project

2. Microevolution and Population Genetics • Evolutionary changes within a population • Gene pool- all the various alleles at all the gene loci in a population • Can study the allelic frequencies of particular loci look at the % who are heterozygous, homozygous • Peppered Moths

3. Microevolution and Population Genetics • After 1 generation, the allelic frequencies are still the same in equilibrium • Sexual reproduction alone cannot bring about a change in genotype and allele frequencies • What other factors must influence change in genotype?

4. Hardy Weinberg Equations • P + Q = 1 • P2 + 2PQ + Q2 = 1 (100%) • P2=frequency of homozygous dominant • P=frequency of dominant allele • 2PQ= frequency of heterozygous dominant • Q2=frequency of homozygous recessive • Q=frequency of recessive allele • 16% of a population has a recessive disease. Calculate the allelic frequencies • check your work • Q2=.16, Q=0.4 (take square root) Q2 = 16% • P + (0.4)=1, P = 1- 0.4 = 0.6 + P2 = 36% • P2=(0.6)2=0.36 or 36% +2PQ= 48% • 2PQ= 2(0.4)(0.6)=0.48 or 48% 1 = 100% Frequency is a number between 0 and 1

5. Hardy-Weinberg Equations • Equilibrium of gene pool frequencies will remain in effect if there are no pressures on the population • Determines allelic frequencies of genes • If frequencies don’t change over time, evolution is not occurring population in equilibrium • Conditions for HW equations to work • Large gene pool (no genetic drift) • Isolation of population (no gene flow) • No mutations can occur • Random mating • No selective pressure for or against traits (no natural selection)

6. Processes That Lead To Microevolution • Mutations-change in the DNA, low rate, not “directed” • Non-random mating-organisms pick their mate, sexual selection, assortative mating • Gene flow-genes move with individuals when they move out or into a population; reduces genetic differences between populations • Genetic Drift-natural disaster causes a crash in population size, allele frequency changes due to chance events Calculate the changes in allele frequencies

7. Processes That Lead To Microevolution • Gene flow-genes move with individuals when they move out or into a population • Mutations-change in the DNA • Non-random mating-organisms pick their mate

8. Processes That Lead To Microevolution • Genetic drift-random fluctuations in allelic frequencies due to chance occurrences, natural disasters • 2 types • Bottleneck effect-stressful situation greatly reduces size of population • Founder effect-a few individuals leave original colony to establish a new one • Both can result in inbreeding, homozygosity, loss of variability

9. 3 Types of Natural Selective

10. Types of Natural Selection • Stabilizing Selection-favors most common (intermediate) phenotype Human birth weight average of 7 lbs Seven-foot-six Yao Ming and his wife, six-foot-two Ye Li, had a baby girl …She weighed seven pounds, six ounces.

11. Types of Natural Selection • Directional Selection-shift in allelic frequency in a consistent direction in response to environmental pressures: peppered moths, pesticide/antibiotic resistance, guppy color

12. Types of Natural Selection • Disruptive Selection-favors the extreme phenotypes; eliminates the intermediate. Finch beak size large and small beaks because only have large, small seeds, predation favors 2 types of snail shells Forest Open

13. Sexual Selection • Adaptive changes in males and females that lead to an increased ability to secure a mate • Female choice • Good gene hypothesis • Runaway (sexy son) hypothesis, the term runaway refers to an exaggeration of the trait until checked by survival cost • Sexual dimorphism • Males larger, more colorful than females Raggiana Bird-of-Paradise

14. Sexual Selection:Male Competition • Cost-benefit analysis benefit of mating worth the cost of competition among males • Dominance hierarchies  higher ranking individuals have greater access to resources vs lower ranking individuals, cost/benefit of dominance • Territoriality types of defense behaviors needed to defend a territory

15. Natural Selection Favors Diversity • Environments change, it would not be beneficial to contain all the alleles that allow an organism to fully adapt to 1 particular environment • Maintenance of variation among a population has survival and consequently reproductive advantages Subspecies of rat snakes represent separate populations

16. Heterozygous Advantage • Heterozygote is favored over the 2 homozygotes • Sickle Cell Anemia, Cystic Fibrosis • Sickle cell mutation in hemoglobin protein is maintained at a high frequency in populations where malaria is prevalent • Recall: 1 copy offers resistance to malaria, but 2 copies results in sickle cell anemia • SS-normal, not resistant • Ss-normal, resistant • ss-sickle cell, resistant • What happens in the US where malaria is not prevalent?