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 single-nucleotide polymorphismschromatid statistically associateddiseasesInternational HapMap Project

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

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?

Hardy Weinberg Equations P + Q = 1 P 2 + 2PQ + Q 2 = 1 (100%) P 2 =frequency of homozygous dominant P=frequency of dominant allele 2PQ= frequency of heterozygous dominant Q 2 =frequency of homozygous recessive Q=frequency of recessive allele 16% of a population has a recessive disease. Calculate the allelic frequencies check your work Q 2 =.16, Q=0.4 (take square root) Q 2 = 16% P + (0.4)=1, P = = P 2 = 36% P 2 =(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

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)

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

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

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

3 Types of Natural Selective

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.

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

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 ForestOpen

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

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

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

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?