Methodology in medical genetics : an introduction to statistical methods / Alan E.H. Emery.

  • Alan Emery
Date:
1986
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Methodology in medical genetics : an introduction to statistical methods / Alan E.H. Emery. Source: Wellcome Collection.

    19/216 (page 5)
    ESTIMATION OF GENE FREQUENCIES 5 recognizable. Assuming that the genotypes are in equilibrium, then the gene frequencies can be estimated if the frequency of the rare homozygote is known. Thus in alkaptonuria (a recessive disorder) which affects about one child in every million: 1 ^ 1 000000 therefore a = —^— ^ 1000 but p + q = I therefore p 1 and the frequency of heterozygous carriers is 2pq or 1/500. The standard error of the estimation of(when the estimate ofis based upon the frequency of homozygotes q'^) is [(1 — q^)IAN]^ where N is the number of individuals in the sample. Thus Pearn (1973) ascertained 9 cases of Werdnig-Hoffmann disease (a recessive disorder) in a total of 231 370 births in the North-East of England. 9 Therefore ^ 231 370 = 0.000039 and q = ^0.000 039 = 0.006 24 /1 - 0.000 039 and SE = / V (4) (231 370) = 0.001 04 The 95% confidence limits will therefore be mean ± 1.96 x SE = 0.00624 ± 1.96(0.00104) = 0.004 20 to 0.008 28 Heterozygote is recognizable If a characteristic is suspected of being determined by two codominant alleles, the heterozygote therefore being recognizable, the frequencies of the two genes can be estimated. Since the frequency of heterozygotes (Я) = Ipq if the disorder is very rare then H