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Bb-Chap.15-Lect.-FA10_1 (1)

Bb-Chap.15-Lect.-FA10_1 (1) - How Are Populations Genes and...

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1 How Are Populations, Genes, and Evolution Related? Changes an individual experiences as it grows & develops are NOT evolutionary changes Evolutionary changes : Occur from generation to generation Cause descendants to differ from ancestors Occur at the population level
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2 The Gene Pool Population : group of organisms of the same species living in a given area Gene pool : sum of all genes in a population at any one time All alleles of all genes in all individuals of a population Allele frequency : frequency (proportion) of each allele in a population
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3 The Gene Pool Example : coat color in hamsters (FIG. 15-2) Population of 25 hamsters contains 50 individual alleles (either B or b at each gene locus) of the coat color gene (hamsters are diploid) If 20 of those 50 alleles are the dominant black coat allele ( B ), then what is the frequency of the black allele?
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4 Evolution Evolution is specifically the change of allele frequencies in a population’s gene pool over time If allele frequencies change from one generation to the next, the population is evolving If allele frequencies do not change from generation to generation, the population is NOT evolving
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5 The Equilibrium Population Hardy-Weinberg principle : under certain conditions , the frequencies of alleles & genotypes in a sexually reproducing population remain constant from one generation to the next Equilibrium population idealized population in which allele freq.’s do not change from generation to generation [Read “A Closer Look: Hardy-Weinberg…” top of page 288 in textbook— used in LAB ! ]
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6 The Equilibrium Population An equilibrium can be maintained as long as ALL 5 of the following conditions are met: 1. No mutation 2. No gene flow between populations 3. Population must be very large 4. Mating must be random 5. No natural selection “Hardy-Weinberg Equilibrium ” = population is NOT evolving
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7 What Causes Evolution? Five factors contribute to evolution : 1. Mutation 2. Gene flow (migration in/out of populations) 3. Small population size 4. Nonrandom mating 5. Natural selection *(these are opposites of equilibrium factors!)
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8 Source of Genetic Variability Mutations in DNA base sequence of gene Usually little or no immediate effect Source of new alleles Passed to offspring only if they occur in cells that give rise to gametes (eggs, sperm) Beneficial, harmful, or neutral Arise spontaneously , not as a result of , or in anticipation of , environmental necessity
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9 WHAT DO THESE RESULTS DEMONSTRATE?
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10 Gene Flow Gene flow : movement of alleles from one population to another --- MIGRATION Immigration adds alleles to a population Emigration removes
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