An introduction to population genetics / by Ching Chun Li.

  • Li, Jingchun.
Date:
1948
Catalogue details

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

Credit: An introduction to population genetics / by Ching Chun Li. Source: Wellcome Collection.

    46/344 (page 30)
    Taking p = .50 + .15 = .65 a nd q — .20 + -15 — .35 we find that % 2 = 34.8. = 5.9). Forone degree of freedom, P = 4 X 10 -9 approximately. Evidently, the observed data is not in agreement with those expected on the basis of Hard'y law. Ts there a satisfactory explana tion to this apparent exception? The author is not familiar with the underlying cause for Ñicoletti's findings but the following possibilities may account for the apparent deviation from that expected: (1) The sample is not a random one or it is too small; (2) the technique of determining the blood types is not entirely trustworthy, (3) there is marked inbreeding among the Sicily population as the observed proportion of heterozygotes (MN type) is too low, and (4) the population understudy is heterogeneous {i. e. consisting of more than one random-mating homogeneous unit). The purpose of citing this example here is to show that sometimes one encoun ters facts apparently contrary to theory and, then, the job is to find out why. For most races, the value of the M-N gene frequency ratio (u) is be tween unity and two; that is, the gene which produces the antigen M is usually more frequent than its allele which is responsible for antigen N- Eskimos and Hindus, however, have very high frequencies of iVf-producing genes, so that the M-N gene frequency ratio is greater than 2 while the Ainus and Australian aborigines have very low M- gene frequency so that the M-N ratio is less than unity. It suffices to say that the gene frequencies are different in the various human races; therefore the study of gene fre quencies is very valuable to anthropologists and historians as well as to gene ticists. A more extensive discussion of this problem would be beyond the scope of this introductory book. § 4. Mother-child combinations It is sometimes, useful to know the frequencies of certain types of mother-child combinations both in theoretical inquiries and in application of legal medicine. These frequencies are of course functions of gene fre quencies. Consider the combination : Mother M-child M. This combination can arise only from the following two matings: ( i) Mother M Father M, frequency in general population = p 2 X p 2 = p^ (ii) Mother' M Father MN, frequency in general population = p 2 X 2 pq = 2 p s q.