Lecture 4 Chapter 23: Evolution of Populations
Lecture 4 Chapter 23: Evolution of Populations Biol 1442
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This 4 page Class Notes was uploaded by Jasmine Rodriguez on Thursday September 8, 2016. The Class Notes belongs to Biol 1442 at University of Texas at Arlington taught by Jill Devito in Fall 2016. Since its upload, it has received 4 views. For similar materials see Ecology and Evolution in Biology at University of Texas at Arlington.
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Date Created: 09/08/16
09/06/2016 BIOL 1442 Lecture 4 Ch. 23 Evolution of Populations ____________________________________________________________________________ ____ From previous sections Violations of HardyWeinberg Equilibrium – are mechanisms of evolution Genetic drift Mutations Natural selection Gene flow among populations Artificial selection Nonrandom mating (sexual selection, assortative mating (mating with similar looking individuals), inbreeding) ____________________________________________________________________________ ____ Chapter 23: Evolution of Populations Question – Pocket mice exhibit polymorphism for coat color (dark vs. light). Which is more fit? Valley of Fire in NM Light colored pocket mice on sand have advantage but dark mice have advantage (10%) and proliferate on the black rocky parts Difference in in 4 nucleotides in MC1r gene In another type of black mice, the dark colored fur was caused by a different genetic mutation This polymorphism was decided by predation Mutations are random. Natural Selection is not random. Geographic Variation gene pool differences among populations B/c what makes them different is the breeding within their own population bc of geographic barriers Cline graded variation in a trait parallels environmental gradient Shorttailed weasel Get larger as it gets more north Bergmann’s rule species get bigger as Alan’s rule – shorter appendages to lose less heat Common for warmblooded animals Hypothesis phenotypic variation in yarrow plants (by altitude) has a genetic component Selection on plants that have a shorter maximum height at higher altitudes. Selection on plants that have a higher maximum height at lower altitudes 09/06/2016 Conclusion genes & environment both contribute to this aspect of plant phenotype “Common Garden Experiment” wild plants from different altitudes were grown in controlled (common) conditions Heights were different in the garden, but not as different as in the wild population Nature and nurture occur simultaneously sometimes Directional Selection natural selection that favors individuals at one end of the phenotypic range Natural selection of one extreme In graph, the bell curve moves to the left or the right Only one direction at a time Diversifying (Disruptive) Selection favors individuals on both extremes of phenotypic range Selects against the medium phenotype In graph, the bell curve splits into two and moves to both left and right Both directions at the same time Stabilizing Selection favors intermediate variants by acting against both extremes Selection against both extremes More medium colored mice In graph, bell curve narrows and Sexual Selection natural selection for mating success; may produce In guppies (and peacocks), females choose the more brightly colored males Sexual Dimorphism – males and females of the same species look very different B/c male looks more colorful than females Intrasexual Selection direct competition (often by males) for mates; male competition They compete and so the bigger and more aggressive males win and get to reproduce 09/06/2016 In salmon, the winning male gets to spawn over the female eggs planted up the stream Male Competition resulting adaptations Examples: antlers, horns, bigger skulls In case of collared lizard, actively look for males in order to fight for their territory but also are brightly colored Intersexual Selection – mate choice; (usually by females) Resulting adaptations: Bright colors, antlers, mating calls, size, etc Female usually is the one who selects b/c she is more invested b/c of offspring care and the limited number of eggs Video distinct male vs. female adult phenotypes (secondary sex characteristics) About jumping spiders are the “peacocks” of spider world Have better eyesight than most spiders Mating ritual – dance and sing Shows how a male spider courts a decoy female spider Polymorphism why would multiple forms persist in a population over many generations? Because over time, one selected phenotype eventually becomes the majority but at that point, it no longer has the advantage and so the opposite phenotype then become the advantage and so the cycle continues Frequency Dependent Selection success of one phenotypic morph declines when it becomes too common in the population The minority has advantage In order for there to be an advantage in using the toll road, there has to be only a few people who use said toll road Balancing (i.e. Frequency Dependent) Selection maintains stable frequencies of multiple phenotypic forms [polymorphism] Sickle Cell Anemia – incomplete dominance RR – normal erythrocytes rr erythrocytes so deformed they cannot carry enough O2 (lethal disease) Rr erythrocytes can carry O2 but not malarial parasite (confers resistance to malaria) “heterozygote advantage” Normal hemoglobin – Glu Sickle Cell Hemoglobin Val Video Explain why the sickle cell allele has not been "weeded out" by natural selection... Because of natural selection of the malaria resistance Frequency Dependent Before modern medicine, sickle cell anemia was lethal Sickle Cell Anemia is not rare High incidence of sickle cell is related to high incidence of malaria Children with the sickle cell were partially protected from malaria and had a lower count of the parasite The mating of two heterozygous parents produce a 1:2:1 ratio. 09/06/2016 The ones with normal hemoglobin can die of malaria The ones with the heterozygotes genes, have the advantage and probably won’t die from malaria Sickle cell disrupts the malaria parasites from being able to reproduce The ones with a homozygous copy of the sickle cell were disadvantages b/c of the inability to adequately transport oxygen in their blood Malaria caused by plasmodium Alternative mating strategies are a fascinating example of frequencydependent selection! Freshwater isopods three different male morphs Beta males mimic females and sneak in to harems Gamma males are tiny and also sneak into harems Alpha males defend harems of females so only they get to reproduce Have to be in the minority in order to have success in mating
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