Human biochemical genetics / by H. Harris.

  • Harris, Harry, 1919-1994.
Date:
1959
Catalogue details

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

Credit: Human biochemical genetics / by H. Harris. Source: Wellcome Collection.

    27/328 (page 15)
    NATURE AND NURTURE I5 to increase the frequency of the more favoured genotypes in the different locaHties. Changes in the environment would tend to result in changes in the frequency of particular genes because the balance of selective pressures would be altered. Thus, paradoxically, dif¬ ferences in the genetical structures of different populations can be a function of the differences in the environments in which they live. The exploration of these possibilities in terms of the biochemical effects of specific genes and their influence on biological fitness in different environments is still in its infancy. One of the complications is that a high frequency of one particular genotype in a population necessarily implies the occurrence of others which may be very different in terms of fitness. For example, it seems very probable that individuals heterozygous for the gene which determines the formation of one type of haemoglobin, haemoglobin S, are at some selective advantage in certain parts of Africa, compared with people not carrying this gene. However, a high frequency of this gene in a population necessarily means that a significant proportion of all children born will be homozygous for it. Such individuals develop a severe anaemia and frequently die in childhood or adolescence. Thus, while the gene in a single dose may be advantageous to the organism, the gene in double dose results in a drastic reduction of fitness. The particular frequency a gene assumes in a given population will reflect the fitness of all the different genotypic combinations in which it may occur. Where several alleles exist, the number of possible combinations at the one locus is increased and the situation becomes increasingly complex. Different genotypic combinations may in general be expected to differ from one another to a greater or lesser degree in any one environment, and their relative differences in fitness to vary from one environment to another. REFERENCES (1) Garrod, A. E. (1902). Lancet, 2, 1616. (2) Garrod, A. E. (1908). Lancet, 2, 1, 73, 142, 214. Ò) Garrod, A. E. (1923). Inborn Errors of Metabolism, 2nd ed. Oxford University Press. (4) Munro, T. A. (1947). Ann. Eugen., Lond. 16, 282. (5) Bertinshaw, D., Lawler, S. D., Holt, H. A., Kirman, B. H. and Race, R. R. (1950). Ann. Eugen., Lond. 15, 234. (6) Tijo, J. H. and Levan A. (1956). Hereditas, 42, 1. (7) Ford, C. E. and Hamerton, J. L. (1956). Acta Genet. 6, 264. (8) Himsworth, H. P. (1949). Lancet, 1, 465.