Studies in quantitative inheritance XI. Genetic and environmental correlation between body size and egg production inDrosophila Melanogaster
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The variation of body size and egg production between individuals of a laboratory population ofDrosophila melanogaster has been examined. Estimates of genetic and environmental contributions to the phenotypic variation have been derivedby comparing the variability of the flies of the wild population with that of genetically uniform flies from crosses between inbred lines reared under similar favourable conditions. Apparently about 50 % of the variance of body size and about 60 % of the variance of egg production is attributable to genetic segregation.
From the results of two-way selection for body size and also egg production, the heritability of the two characters is estimated as respectively 0.43 and 0.18, suggesting that most of the genetic variation in body size behaves as additive in the statistical sense, while non-additive effects predominate in the variability of egg production.
There is a clear-cut phenotypic correlation between size and egg production among the individuals of the wild population and this is mostly genetic in origin. Selection for large and small size leads to comparatively little change in egg production. A series of different genotypes, each represented by a number of genetically identical individuals; were prepared by combining haploid sets of chromosomes from the wild population with a haploid set from an inbred line—and these provided no evidence of genetic correlation between size and egg production. Hence the genetic correlation in the wild stock is essentially non-additive in behaviour.
Gene-environment interaction has been demonstrated for both egg production and body size by comparing estimates of variance and heritability on the live medium with those found on a synthetic medium which permits normal growth. It is suggested that gene-environment interaction will be particularly important under the suboptimal condition in which the population usually lives.
Reduction of the body size of genetically uniform flies by varying the nutrition of the larvae leads to a proportional reduction in the rate at which eggs are laid.
The variability of development time has also been examined in preliminary experiments which indicate that about half the variance is genetic in origin. Under favourable conditions there is a high correlation between length of development and body size, while egg production tends to be negatively correlated, suggesting that egg production and growth rate are genetically associated.
The results are discussed in relation to the stability of average body size in. the population and the ease with which selection either way leads to striking change. There are strong indications that the apparently continuous variation of attributes such as size or egg production are heterogeneous with respect to the effects on physiology and development which contribute to the final variation, while the relative contribution of different sorts of effect may vary according to environmental conditions.
- Gordon, C. &Sang, J. H. (1941). The relation between nutrition and exhibition of the geneantennaless (Drosophila melanogaster).Proc. Roy. Soc. B,130, 151–84.Google Scholar
- Hogben, L. T. (1933).Nature and Nurture. London.Google Scholar
- Kempthorne, O. (1954). The correlation between relatives in a random mating population.Proc. Roy. Soc. B,143, 103–13.Google Scholar
- Reeve, E. C. R. (1954). Natural selection for body size inDrosophila. IXth Int. Congr. Genetics, Abstract.Caryologia, vol. suppl. 1954.Google Scholar
- Robertson, F. W. (1955). Selection response and the properties of genetic variation.Cold Spr. Harb. Symp. Quant. Biol. 20, 166–177.Google Scholar
- Robertson, F. W. &Sang, J. H. (1944). The ecological determinants of population growth in aDrosophila culture. I. Fecundity of adult flies.Proc. Roy. Soc. B,132, 258–89.Google Scholar
- Sang, J. H. (1956). The quantitative nutritional requirements ofDrosophila melanogaster.J. Exp. Biol. 33, 45–72.Google Scholar
- Woole, B. (1952). Environmental effects in quantitative inheritance. InQuantitative Inheritance, ed. Reeve & Waddington. London: H.M.S.O.Google Scholar