ABSTRACT
At the dawn of its second century genetics accepts gradation between major genes and polygenes and an intimate connection between linkage and allelic association. Half a century ago these propositions were contentious. Fisher (1918) devised a calculus of variances for quantitative traits that united Mendelism with biometry and became a discipline for plant and animal breeding and behaviour genetics. Mather (1949) preferred variances to gene identification and briefly postulated that polygenes lie in heterochromatin while major genes reside in euchromatin (Mather, 1944). Polymorphism was believed to be rare and maintained by selection (Ford, 1940). In conformity to that dictum, population geneticists attributed allelic association to epistatic selection acting in mathematically clever ways that could not be tested (Lewontin and Kojima, 1960; Arunachalam and Owen, 1971).
