Estimates of genetic parameters from a hybrid derivative in Nicotiana.

I N 1918, FISHER described the genotypic variance as consisting of additive genetic, dominance, and epistatic components. This model was later extended by FISHER, IMMER, and TEDIN (1932) to include the action of any number of genes in the absence of epistasis. WRIGHT (1935) presented a model dealing with epistatic effects of loci in pairs, as has GRIFFING (1950) in a constant parent regression procedure. Three genetic models which include epistatic parameters have been developed independently by COCKERHAM (1954) for a random mating population and by ANDERSON and KEMPTHORNE (1954) and HAYMAN and MATHER (1955) for populations derived from inbred lines. Theoretical considerations suggest that epistasis may play an important role in determining genetic differences in certain situations. Most experimental evidence has been indirect, being derived from expectations based upon simple additivity. In such cases, a number of investigators have postulated the existence of nonallelic interactions to account for observed deviations from linearity. However, quantitative estimates of epistatic effects have been more limited. In presenting their model, ANDERSON and KEMPTHORNE (1954) made applications to two sets of data. HORNER and WEBER (1956) included a digenic interaction component, additive x additive, in an analysis of variances and covariances, as did MATZINGER, MANN and ROBINSON (1960), BRIM and COCKERHAM (1961), and HANSON and WEBER (1961). More recently attempts have been made to estimate more than one interaction parameter in populations derived from inbred lines. Applications of the diallel analysis described by JINKS (1954) and HAYMAN (1954) which provide estimates of more than one epistatic interaction parameter have included inbred lines from the genus Nicotiana (HAYMAN 1958, 1960; JINKS and JONES 1958; POVILAITIS 1964). SMITH (1968) has recently reviewed the investigations on quantitative gene action in Nicotiana. The present paper describes the estimation of three epistatic components, as well as additive and dominance components of an inbred line derived from hybridization. A preliminary report of this investigation has been published previously (DALY 1958).