Balanced Combinations of Polygenes

Abstract

OUR criticism of Scharloo's publication has done its work in eliciting replies and demonstrating that whether, and if so when and where, polygenic balance arises through selection operating on effects- of genes on bristle number, or on pleiotropic effects of those genes, through linkage of those genes to others with more drastic effects on fitness or through random effects, is a more open problem than Scharloo suggests. Prof. Mather points out to us that it has also shown the dangers of taking statements out of their context, for his comment, quoted by Scharloo, that “Pleiotropy in the classical sense is therefore almost useless as a concept for application in biometrical genetics” followed a discussion of the difficulty, general with a biometrical methodology as distinct from classical, of analysing into their ultimate units groups of linked genes (or effective factors as Mather called them) which might indeed be expected to show apparently pleiotropic action (just as they can show apparent over-dominance) even where the ultimate genes themselves did not. The effective factor is the finest unit whose properties biometrical genetics will normally reveal; but its pleiotropy cannot be held to imply pleiotropy of the genes which compose it, and indeed in cases which Mather has analysed demonstrably does not do so.