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
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?