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25.1 Genotypic and Allelic Frequencies Are Used to Describe the Gene Pool Of a Population

25.1 Genotypic and Allelic Frequencies Are Used to Describe the Gene Pool Of a Population. Calculating genotypic frequencies F = No.AA individuals/N N: total no. of individuals F: frequency of AA alleles. Calculating allelic frequencies

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25.1 Genotypic and Allelic Frequencies Are Used to Describe the Gene Pool Of a Population

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  1. 25.1 Genotypic and Allelic Frequencies Are Used to Describe the Gene Pool Of a Population • Calculating genotypic frequencies • F = No.AA individuals/N • N: total no. of individuals • F: frequency of AA alleles. • Calculating allelic frequencies • Frquency of an allele = No. copies of the alleles/No. copies of all alleles at the locus in a population.

  2. 25.2 The Hardy-Winberg Law Describes the Effect of Reproduction on Genotypic and Allelic Frequencies • Hardy-Weinberg Law • Assumption: population is large, randomly mating, not affected by mutation, migration, or natural selection. • Prediction 1: the allelic frequencies of a population do not change. • Prediction 2: the genotypic frquencies stabilize.

  3. Genotypic frequencies at H-W equilibrium • p + q = 1 • p2 + 2pg + q2 = 1 • P2: homozygous dominant allele pair frequency. • Q2 :homozygous recessive allele pair frequency. • 2pq: heterozygous allele frequency.

  4. Concept Check 1 What is the expected frequency of heterozygotes in a population with allelic frequency X and Y that is in H-W? • X + Y • XY • 2XY • (X- Y)2

  5. Concept Check 1 What is the expected frequency of heterozygotes in a population with allelic frequency X and Y that is in H-W? • X + Y • XY • 2XY • (X- Y)2

  6. 25.3 Nonrandom Mating Affects the Genotypic Frequencies of a Population • Positive assortative mating: • a tendency of like individuals to mate. • Negative assortative mating: • A tendency of unlike individuals to mate.

  7. Inbreeding • Increases frequency of homozygotes in population • Rate is affected by how closely related mating pairs are

  8. Concept Check 2 What is the effect of outcrossing on a population? • Allelic frequency changes in the population. • More heterozygotes will be produced in the population. • Fewer heterozygotes will be produced. • It will reach the H-W equilibrium

  9. Concept Check 2 What is the effect of outcrossing on a population? • Allelic frequency changes in the population. • More heterozygotes will be produced in the population. • Fewer heterozygotes will be produced. • It will reach the H-W equilibrium

  10. 25.4 Several Evolutionary Forces Potentially Cause Changes in Allelic Frequencies • Mutation • Migration • Genetic Drift • Founder effect • Genetic bottle neck • Natural selection

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