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Unformatted text preview: BIOLOGY UNT IV EXAM OUTLINE NATURAL SELECTION When an allele is favored by selection, whether it is dominant or recessive will change the rate at which it reaches fixation in a population , but will not change the ultimate outcome Example: Tay-Sachs disease (completely lethal before reproduction) o W A/A = 1.00 o W A/a = 1.00 o W a/a = 0.00 After fertilization: o A/A = 0.81 p 2 W A/A = 0.81 x 1.0 = 0.81 o A/a = 0.18 2 pq W A/a = 0.18 x 1.0 = 0.18 o a/a = 0.01 q 2 W a/a = 0.01 x 0.0 = 0.00 Adds up to 0.99, so to arrive at the genotype frequencies in the next generation we divide through by the mean fitness of the population, W. o A/A = 0.81 p 2 W A/A = 0.81 A/A = 0.81/0.99 = 0.818 o A/a = 0.18 2 pq W A/a = 0.18 A/a = 0.18/0.99 = 0.182 o a/a = 0.01 q 2 W a/a = 0.00 a/a = 0.00/0.99 = 0.00 o A/A = 0.818 o A/a = 0.182 o a/a = 0.00 The sickle-cell allele causes mutations in hemoglobin but also confers malaria resistance It exemplifies heterozygote advantage & balancing selection In frequency-dependent selection, the fitness of any morph declines if it becomes too common in the population o Example is the scale eating fish that are right and left mouthed Darwins Postulates: 1. Individuals vary 2. At least some variation is heritable 3. Some individuals leave more progeny than others 4. The variation in survival and reproduction is not random, but depends on heritable trait variation o Outcome: (genetic) variants with higher survival and/or reproduction increase in frequency in population Sexual Selection o Natural selection for mating success o Can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics peacocks o Intrasexual selection is competition among individuals of one sex for mates of the opposite sex (males fighting for mates) o Intersexual selection occurs when individuals of one se (usually females) are choosy in selecting their mates from individuals of the other sex may depend on the showiness of the males appearance SPECIATION Speciation is the origin of new species and is at the focal point of evolutionary theory Micoevolution consists of adaptations that evolve within a population, confined to one gene pool Macroevolution refers to evolutionary change above the species level Chapter 24 Biological species concept - a species is a group of population whose members have the potential to interbreed in nature and produce viable fertile offspring Reproductive Isolation - the existence of biological factors ( barriers) that impede members of two species from producing viable, fertile offspring Reproductive isolation increases with time of separation Gene flow is the movement of gametes or individuals between populations resulting in genetic changes in a population (for example, changes in allele frequencies) The critical issue is the reduction of gene flow between populations, so that populations can diverge in...
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