Population GeneticsPopulation-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

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 EquationsP + Q = 1 P2 + 2PQ + Q2 = 1 (100%)P2=frequency of homozygous dominantP=frequency of dominant allele2PQ= frequency of heterozygous dominantQ2=frequency of homozygous recessiveQ=frequency of recessive allele

16% of a population has a recessive disease. Calculate the allelic frequencies

check your workQ2=.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

Hardy-Weinberg EquationsEquilibrium of gene pool frequencies will remain in effect if

there are no pressures on the populationDetermines allelic frequencies of genesIf frequencies don’t change over time, evolution is not

occurring population in equilibriumConditions for HW equations to workLarge gene pool (no genetic drift)Isolation of population (no gene flow)No mutations can occurRandom matingNo 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 typesBottleneck 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

Forest Open

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 FibrosisSickle 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 resistantSs-normal, resistantss-sickle cell, resistantWhat happens in the US where

malaria is not prevalent?