Alicia WalkerZoology 101 – McIntyre – Microevolution - 23 Apr 2012HOW do species change? Through microevolution (Ex: different colorations of butterflies & humans) and macroevolution- Frequencies of sickle-cell allele - Distrubution of malaria caused by Plasmodiumfalciparum (cerebral malaria, kills within 24-36 hours), parasitic unicellular eukaryotes. - On the map of Africa, if the area has lowerfrequency of sickle-cell allele it means thatthere is less resistance to malaria- More than 12.5% has higher immunity to malaria Macroevolution: large – new species; Generation 103+Microevolution: small – same species; Generation 100-102Genetic variation within populationsIndividual heterozygosity – having different alleles at a gene locusAverage heterozygosity – percent (%) of loci that are heterozygous across genome in a typical individual.Drosophila (fruit fly): heterozygous at 14% of loci yet only 1% of nucleotides differ Origin/Sources of new allelesMutation – sequence of change that forms a new alleleGene duplication – new copies can serve new purposes (i.e. olfaction [smell])Immigration – inflow of existing alleles (form another population) Shuffling allelesSexual reproduction – mixes alleles in each generation Mechanisms of microevolution1) Natural selection – growth, survival, and reproduction 2) Sexual selection – mating success3) Genetic drift – random shifts in allele frequencies4) Gene flow – immigration of allelesNatural Selection – enhanced growth, survival, and reproduction leadto changes in allele frequencies (which leads to adaptation)Alicia WalkerDirectional selection: pushedevolutionary changed in one way(image, bottom far left)Disruptive/diversifying selection:bimodal distribution (very little changein middle); one end or the other aretwo (2) dominate phenotypic traits(image, bottom middle)Balancing (stabilizing) selection: eliminating both the extremes, andthere is a median evolution in themiddle (image, bottom far right)Sexual selection – enhanced mating success leads tochanges in allele frequencies- Intrasexual competition vs. Female (mate) choice(Ex: birds of paradise)o Male frogs make louder calls (naturalselection against them, because ofpredation and chances of higher chances offemales mating with them)o Intrasexual competition (males competewith each other for females Genetic drift - Drift = change in allele frequencies by chance-Situation #1: Traits that are selectively neutral o Human fingerprints have no known selective value, yet adermatoglyphia is rare (just 4 families have this worldwide!) o Adermatoglyphia – no fingerprints-Situation #2: o Founders effect – random shifts as newpopulation goes from small to large-Situation #3:Alicia Walkero Population bottleneck – random shifts as existing population goes form large to small to largeo Disaster or catastrophic evento Conceivable, drift can lead to adaptive change but only by chancGene flow: exchange of alleles among populations byimmigration of individuals - Great Tit birds [Species name: Parus major] - High immigration from mainland - Island off coast of Netherlands- No gene flow between mainland & easternpopulation- But gene flow is central & central population - Mainland had an island specific allele(interbreeding meant lower survival rate; alsoit lead to messed up allele frequencies)Observed genetic variation within populations- Spatial variation is ubiquitouso Enhanced by differences in environmento Decreased by gene flow, which preventsindependent drift- Cline in allele for cold tolerances (spatial variation)o Marine (higher population with this allele) Cold Water - 6°Co Georgia (lowere population with this allele) Warmer Water - 21°C o This variatoiin is decreased by gene flow o Mot moving back and forth between Maine and Georgia for these fishAlicia Walker- Temporal variation is poorlyunderstoodo Enhanced by consistency ofdifferences in environment o Decreased by gene flow, whichprevents independent driftso Right-mouthed fish favorabletrait o Can also be left-mouthed fishfavorable trait; it alternateso Frequency-dependence selection Enhanced by “consistence” of difference in environment Decreased by gene flow, which prevents independent drift Additional topics:Hardy-Weinberg principle – the principle that frequencies of alleles and genotypes in a population remain constant from generation to generation, provided that only Mendelian segregation and recombination of alleles are at work p2 + 2pq + q2 = 1Conditions of Hard-Weinberg Equilibrium1) No mutations. The gene pool is modified if mutations alter alleles or if entire genes are deleted or duplicated.2) Random mating. If individuals mate preferentially within a subset of the population, such as their close relatives (inbreeding), random mixing of gametes does not occur, andgenotype frequencies change.3) No natural selection. Differences in the survival and reproductive success of individuals carrying different genotypes can alter allele frequencies.4) Extremely large population size. The smaller the population, the more likely it is that allele frequencies will fluctuate by chance from one generation to the next (a process called genetic drift)5) No gene flow. By moving alleles into or out of populations, gene flow can alter allele frequencies. Big-Picture Conclusions:1) Microevolution has given rise to extensive spatial & temporal variation in allele frequenciesAlicia Walker2) Despite new alleles & genetic drift and flow existing alleles, natural selection drives adaptive microevolution.PRE-LECTURE QUIZ1) Which of the following is not true? Individual organisms evolve2) Quantitative characters represent the majority of heritable genetic variation. These characters are traits that: Vary along a continuum within a population3) Which of the following is the correct comparison of gene (or allele) variability versus nucleotide variability? Gene variability > nucleotide variability4) Which of these contribute to genetic variation in natural populations? All of these contribute to genetic variation5) Nucleotide mutation rates per year are highest in: RNA viruses6) Based on the Hardy-Weinberg principle, what is the expected frequency of heterozygotes in a population with p=0.7 and q=0.3?7) Which of the following violates the assumptions of Hardy-Weinberg equilibrium? A recent population bottleneck 8) Which of the following consistently causes adaptive evolution? Natural
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