The manifold effect of selection

On biometrical genetics

“…The use of such markers early provided evidence that at least some of the determinants of continuous variation must be carried on the chromosomes, and later, through the now highly developed technique of chromosome assay, that where the test could be applied all, or virtually all, of these determinants must be nuclear (see Mather and Harrison, 1949). In recent years, Thoday (1961) and his colleagues have gone further, and using the special stocks available in Drosophila melanogaster have shown how, under favourable circumstances, components of a polygenic system can be related to specific loci in the chromosomes.…”

Polygenic variability in chromosomes of Drosophila melanogaster obtained from the wild

“…Previous experience had accorded with this view, it having been observed in particular that :-(i) the speed and extent of advance under selection is the greater the more widely different, in respect of gene content, the parental lines are expected from their origin to be (Mather, iL.i Sismanidis, 1942) ; (ii) the changes wrought by selection have a determinacy which would be difficult to understand if they depended on differences arising by mutation (Sismanidis, 1942 ;Mather and Harrison, 1949) ; (iii) change in homozygous lines, where selection must utilise variation arising de novo, is very slow (Mather, 1941 ;Mather and Wigan, 1942).…”

“…But even taking the bare minimum of five differences in these second chromosomes (assuming the change in B/B to be due to a gene in chromosome II), it is clear that the variation must be regarded as polygenic. It must be remembered, too, that Mather and Harrison (1949) found evidence of at least two gene differences affecting this character in chromosome X and at least three in chromosome III. Gene differences are, in fact, ubiquitous and it is pointless to argue whether there are only ten (which good fortune has enabled us to unearth so readily) or whether there are really a hundred of which the ten are a chance sample and whether the ten differences are in single genes or in compound effective factors (Mather, 1949).…”

Assortative mating for a metrical characteristic in Drosophila

“…Mather and Harrison (1949) showed mating preferences for two wild type stocks of flies and selected lines derived from them. Santibañez and Waddington (1958) summarised many of the earlier relevant experiments in Drosophila, and showed a tendency for positive assortative mating for a series of inbred lines in experiments they carried out.…”