Hardy weinberg supplement
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The document discusses the Hardy-Weinberg law of population genetics, which explains how allele and genotype frequencies remain constant over generations under specific conditions. It outlines the four assumptions necessary for Hardy-Weinberg equilibrium and illustrates how to calculate allele frequencies and genotypic ratios using real-world examples. Additionally, it addresses factors that can lead to deviations from this equilibrium and provides guidance on maintaining ideal population conditions.
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Hardy weinberg supplement
- 1. Hardy-Weinberg Law of Population Genetics Prepared by Pratheep Sandrasaigaran Lecturer at Manipal International University
- 2. Constant Allele Frequencies • Population genetics looks at phenotypes and genotypes among large numbers of individuals. • Tracking allele frequencies from one generation to the next can reveal evolution in action. Prepared by Pratheep Sandrasaigaran
- 3. Hardy-Weinberg Equilibrium • In 1908 Godfrey Harold Hardy (mathematician) and Wilhelm Weinberg (German physician). • Independently (never met) used algebra to explain how genotypic frequencies are related to allele frequencies. Prepared by Pratheep Sandrasaigaran
- 4. Relating alleles to genotypes • What is an equilibrium? • What is Hardy-Weinberg equilibrium? • Allele and genotype frequencies will remain unchanged, generation after generation, as long as certain conditions are met; four assumptions. • When one of the assumptions isn’t met, the relationship between allele frequency and genotype frequency usually starts to fall apart Prepared by Pratheep Sandrasaigaran
- 5. Four conditions for Hardy- Weinberg Equilibrium • The organism must reproduce sexually and be diploid. • The allele frequencies must be the same in both sexes. • The loci must segregate independently. • Mating must be random with respect to genotype Prepared by Pratheep Sandrasaigaran
- 6. Graphically illustrated Hardy- Weinberg Equilibrium • The Y axis is genotypic frequency in percentage. • The X axis is the frequency of the recessive allele in percentage. • What proportion of the population is homozygous aa when the allele frequency of a is 40 percent? • 20 percent of the population is expected to be aa when 40 percent of the population carries the a allele Prepared by Pratheep Sandrasaigaran
- 7. Relating alleles to genotypes • If frequency of allele a is 40%, then the frequency of allele A is 60%, because p + q = 1. • What is this line for? • The frequency of heterozygotes, Aa. • The highest proportion of the population that can be heterozygous is 50 percent Prepared by Pratheep Sandrasaigaran
- 8. Relating alleles to genotypes • When 50 percent of the population is heterozygous, the Hardy-Weinberg equilibrium predicts that 25 percent of the population will be homozygous for the A allele, and 25 percent will be homozygous for the a allele. • This situation occurs only when p is equal to q. • p = q = 50% Prepared by Pratheep Sandrasaigaran
- 9. Relating alleles to genotypes • The relationship between allele frequencies and genotype frequencies is described by the equation p2 + 2pq + q2 . • Thus, the line marked aa is described by the equation p2 . • The line marked AA is described by the equation q2 . • 2pq describes the frequency of heterozygotes (Aa) Prepared by Pratheep Sandrasaigaran
- 10. Violating the law • There are several ways that populations can wind up out of Hardy-Weinberg equilibrium. • How to ensure no violation? – Large population – No mutation – No natural selection – No migration – Randomly mating populations Prepared by Pratheep Sandrasaigaran
- 11. Solving a Problem • Consider an autosomal recessive trait: a middle finger shorter than the second and fourth fingers. • If we know the frequencies of the dominant and recessive alleles, then we can calculate the frequencies of the genotypes and phenotypes and trace the trait through the next generation. Prepared by Pratheep Sandrasaigaran
- 12. Solving a Problem • The dominant allele D confers normal-length fingers; the recessive allele d confers a short middle finger. • If 9 out of 100 individuals in a population have short fingers (dd) —the frequency is 9/100 or 0.09. • Since dd equals q2 , then q equals 0.3. • Since p + q = 1.0, knowing that q is 0.3 tells us that p is 0.7 Prepared by Pratheep Sandrasaigaran
- 13. Solving a Problem • Calculate the proportions of the three genotypes that arise when gametes combine at random. • Homozygous dominant = DD (p2 ) • 0.7 × 0.7 = 0.49 • Homozygous recessive = dd (q2 ) • 0.3 × 0.3 = 0.09 • Heterozygous = Dd + dD (2pq) • (0.7)(0.3) + (0.3)(0.7) = 0.42 Prepared by Pratheep Sandrasaigaran
- 14. Solving a Problem • Within a population of mouse, the color black (B) is dominant over the white color. 40% of all mice are white. Calculate the following – The percentage of mice in the population those are heterozygous. – The frequency of homozygous dominant individuals Prepared by Pratheep Sandrasaigaran