Reminder genotype frequencies are the frequencies of

This preview shows page 9 - 11 out of 16 pages.

Reminder:Genotype frequenciesare the frequencies of the three possible genotypes (AA, Aa, aa). Allele frequenciesare the frequencies of the two alleles (A with frequency p; a with frequency q)In general:Solving population genetics problems usually follows this pattern: (1) Find the allele frequencies; there are 2 methods to use depending on what you know: (1a) if you know all the genotype frequencies (1b) if you know at least one of the genotype frequencies andcan assume that the population is at HWE. You can then find the other genotype frequencies. (2) Predict the genotype frequencies in the next generation. (3) See if the population is at HWE. The particular steps:(1a) Find the allele frequencies given all three genotype frequencies. This is the most general way to get allele frequencies; it works under allconditions (at HWE and not at HWE). You do it by calculating the number of alleles contributed by each genotype to the gene pool. • since each individual has two alleles to contribute, the size of the gene pool is the number of individuals times 2. • each AA individual contributes 2 A’s to the pool • each Aa individual contributes one A and one a to the pool • each aa individual contributes 2 a’s to the pool For example: given this population genotypenumberAA 30 Aa 20 aa 50 you calculate the total # of individuals = 30 + 20 + 50 = 100; this lets you calculate the genotype frequencies: genotypenumbergenotype frequency (number divided by total)AA 30 30/100 = 0.3 Aa 20 20/100 = 0.2 aa 50 50/100 = 0.5 Now, you can get the allele frequencies in two ways: either calculate the contributions using the numbersof each genotype (easy): contributions to gene pool genotypenumbertotal allelesA allelesa allelesAA 30 60 60 Aa 20 40 20 aa 50 100 0 total # of alleles = 100 x 2 = 200 (or 60 + 40 + 100 = 200) total # of A’s = 60 + 20 = 80 frequency of A = p = 80/200 = 0.4 total # of a’s = 20 + 100 = 120 frequency of a = q = 120/200 = 0.6
0
20
100
Evolution 6 - 10 or calculate using the frequencies of each genotype (more advanced): frequency of A = p = (frequency of AA) + (frequency of Aa)/2 = 0.3 + (0.2)/2 = 0.3 + 0.1 = 0.4 frequency of a = q = (frequency of aa) + (frequency of Aa)/2 = 0.5 + (0.2)/2 = 0.5 + 0.1 = 0.6
(1b) Find the allele frequencies given at least one genotype frequency andassuming the population is at HWE. This

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture