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Evolution and Populations –Essential Questions p. 431-435
How can a lethal gene exist in a gene pool and not disappear? What is genetic drift? Explain each of the three different types of genetic drift. According to the Hardy-Weinberg Principle, what five things must occur to prevent genetic drift? 5. When do mutations pass from one generation to the next?
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Population Genetics
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Alleles that are lethal in a homozygous individual may be carried in a heterozygote and thus maintained in a gene pool. Know the conditions for Hardy-Weinberg equilibrium in a population and why these conditions are not likely to appear in nature. Know how to solve the Hardy-Weinberg equation to predict the frequency of genotypes in a population, given the frequency of phenotypes.
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– genes have at least two alleles
Genetic Variation – genes have at least two alleles Gene Pool – all genes, including all of the different alleles, present in a population
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Relative Frequency – the number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur - evolution is any change in the relative frequency of alleles in a population
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Genetic Drift Stabilizing selection Disruptive Selection
Directional Selection
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Lethal genes remain in a gene pool at low frequency if they are recessive. They are carried by hybrids (heterozygous individuals).
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Sources of Genetic Variation
Mutations – changes in a DNA sequence - additions, deletions, substitutions of nucleotides, and rearrangement of chromosomes neutral, harmful, or beneficial to be passed on they must be in sex cells
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Hardy-Weinberg Principle
Genetic Equilibrium – allele frequencies remain constant as long as there remains: 1. random mating 2. a very large population 3. no movement into or out of the population 4. no mutations 5. no natural selection *** NOT likely to happen in nature
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p2 + 2pq + q2 =1 p + q = 1 2pq = % of Aa q2 = % of aa
p2 = % of AA 2pq = % of Aa q = % of aa q = # of a alleles p = # of A alleles
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Use the chart to determine the frequency of the AA genotype
Use the chart to determine the frequency of the AA genotype. What is the frequency of the A allele? Flowers(population 100) AA Aa aa
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