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Two individuals, G. H. Hardy & W. Weinberg, showed mathematically that for any given gene present in a population of individuals (diploid and sexually reproducing), the allele and genotype frequencies will not change from generation to generation (forever) if three conditions are met: 1. The population of individuals carrying this gene is infinitely large. 2. Individuals in this population mate randomly with respect to this gene (s). 3. There are no evolutionary forces acting upon this gene (natural selection, genetic drift, migration, mutation, etc) Hardy & Weinberg devised a formula that shows the relationship between allele frequencies and genotype frequencies when the three conditions mentioned above are met; this is known as the Hardy-Weinberg Formula. Q. What is the formula? A. The formula for a gene with 2 possible alleles is: (p q)2 = 1, which is the same as p2 2pq q2 = 1 Where p = frequency of one allele and q = frequency of the other allele p2 = expected freq. of homozygotes for one allele 2pq = expected freq. of heterozygotes q2 = expected freq. of homozygotes for the other allele Q. What if I am dealing with a gene with more than 2 alleles, what formula do I use? A. The formula is basically the same except the number of allele frequencies plugged into the formula increase. For example, a gene with 3 possible alleles (Eg. A1, A2, A3) will have the formula: (p q r)2 = 1, which is the same as p2 q2 r2 2pq 2pr 2qr = 1 Where p = freq. of the first allele, q = freq. of the second allele and r = the frequency of the third allele. p2 = Freq. of homozygotes for first allele q2 = Freq. of homozygotes for second allele r2 = Freq. of homozygotes for third allele 2pq = Freq. of heterozygotes for first and second allele 2pr = Freq. heterozygotes for first and third allele 2qr = Freq. heterozygotes for second and third allele Q. What good is this formula? Why bother using it? A. If you are studying a gene (s) in a particular population, you can use the allele frequencies that you have estimated from a sample of this population to generate expected genotype frequencies for that population (by plugging your allele frequencies into the Hardy-Weinberg Formula). If the genotype frequencies you get by using the Hardy-Weinberg Formula are not the the frequencies you actually observe in your sample, then one of the three assumptions outlined above (top of page) are not being met. Consequently, you have a basis for investigating the reasons why. This is the investigation of why and how gene frequencies change in populations over time--in effect, the study of evolution. #Proteins #HardyWWeinberg #genes #phenotype #geneExpression #DNA #mutation #migration #geneticDrift #Cancer #Genetics101 #NaturalSelection #gene #generation #GeneticsLecture #Allele #genotypeFrequencies #GeneticsExamQuestionsSolutions #GeneticTesting #alleleFrequenciesAndGenotypeFrequencies #GeneticExamQuestionsSolutions #genotype #MolecularBiology #genomes #geneticCode #chromosome #PopulationGeneticsFieldOfStudy #alleles #Genetics #NikolaysGeneticsLessons
