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Genetic variation in populations can be analyzed and quantified by the frequency of alleles. Two fundamental calculations are central to population genetics: allele frequencies and genotype frequencies.〔Brooker R, Widmaier E, Graham L, and Stiling P. ''Biology'' (2011): p. 492〕 Genotype frequency in a population is the number of individuals with a given genotype divided by the total number of individuals in the population.〔Brooker R, Widmaier E, Graham L, and Stiling P. ''Biology'' (2011): p. G-14〕 In population genetics, the genotype frequency is the frequency or proportion (i.e., 0 < ''f'' < 1) of genotypes in a population. Although allele and genotype frequencies are related, it is important to clearly distinguish them. Genotype frequency may also be used in the future (for "genomic profiling") to predict someone's having a disease or even a birth defect.〔(【引用サイトリンク】title=Neural Tube Defects: an Evaluation of Genetic Risk )〕 It can also be used to determine ethnic diversity. ==Numerical example== As an example, let's consider a population of 100 four-o-'clock plants (''Mirabilis jalapa'') with the following genotypes: *49 red-flowered plants with the genotype AA *42 pink-flowered plants with genotype Aa *9 white-flowered plants with genotype aa When calculating an allele frequency for a diploid species, remember that homozygous individuals have two copies of an allele, whereas heterozygotes have only one. In our example, each of the 42 pink-flowered heterozygotes has one copy of the a allele, and each of the 9 white-flowered homozygotes has two copies. Therefore, the allele frequency for a (the white color allele) equals : This result tells us that the allele frequency of a is 0.3. In other words, 30% of the alleles for this gene in the population are the a allele. Compare genotype frequency: let's now calculate the genotype frequency of aa homozygotes (white-flowered plants). : Allele and genotype frequencies always sum to less than or equal to one (in other words, less than or equal to 100%). The Hardy–Weinberg law describes the relationship between allele and genotype frequencies when a population is not evolving. Let's examine the Hardy–Weinberg equation using the population of four-o'clock plants that we considered above: if the allele A frequency is denoted by the symbol p and the allele a frequency denoted by q, then p+q=1. For example, if p=0.7, then q must be 0.3. In other words, if the allele frequency of A equals 70%, the remaining 30% of the alleles must be a, because together they equal 100%.〔Brooker R, Widmaier E, Graham L, and Stiling P. ''Biology'' (2011): p. 492〕 For a gene that exists in two alleles, the Hardy–Weinberg equation states that (''p''2) + (2''pq'') + (''q''2) = 1 If we apply this equation to our flower color gene, then : (genotype frequency of homozygotes) : (genotype frequency of heterozygotes) : (genotype frequency of homozygotes) If p=0.7 and q=0.3, then : = (0.7)2 = 0.49 : = 2×(0.7)×(0.3) = 0.42 : = (0.3)2 = 0.09 This result tells us that, if the allele frequency of A is 70% and the allele frequency of a is 30%, the expected genotype frequency of AA is 49%, Aa is 42%, and aa is 9%.〔Brooker R, Widmaier E, Graham L, and Stiling P. ''Biology'' (2011): p. 493〕 Genotype frequencies may be represented by a De Finetti diagram. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Genotype frequency」の詳細全文を読む スポンサード リンク
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