Estimation of the Components of Heterosis

J L Jinks, R M Jones
1958 Genetics  
N previous papers (JINKS 19544,1956) the analysis of the parents, F,'s, F2's and I backcross generations of an 8 x 8 diallel between inbred varieties of Nicotiana rustica using the method of diallel analysis described by JINKS and HAY- MAN (1953), and extended by SINKS (1954), HAYMAN (1954), DICKINSON and JINKS (1956) and JINKS (1956) have been presented. They showed that nonallelic interactions, as well as additive and dominance effects, play an important role in the inheritance of all the
more » ... e characters followed, namely, final height, time of flowering and leaf size. This finding was subsequently confirmed for a number of diallel sets of crosses in other species where a wide range of characters were followed (JINKS 1955; ALLARD 1956) . What is more important to our present discussion, however, was the finding that the F, generation of crosses showing nonallelic interactions were in general superior in their performance to those of noninteracting crosses. This appears to implicate nonallelic interactions as a major source of heterosis, and we shall now attempt to assess the magnitude of their contribution relative to those of the other components of heterosis. T h e components of heterosis If we define heterosis as the difference between the mean of a n F, family and that of its better parent, the expectations can be expressed in terms of the genetic parameters for additivity ( d ) and dominance ( h ) (MATHER 1949) and the nonallelic interaction components (i, j , and 2) of HAYMAN and MATHER (1955) together with parameters expressing the degree of association or dispersion of the genes in the homozygous parents. Consider first the case in which all genes have similar effects, and all pairs of genes similar interactions. Let the parents P, and P, differ at k loci, and of these let P, have k' of greater effect. Of the l/zk ( k -1 ) pairs of loci, k' ( kk') are dispersed and the remainder associated. The mean parental phenotypes are then T s ( k -2 k ' ) ( k -1 ) j + % k(k-1)Z. If, now, we write r = 1 -2k' k --kr2-1 this becomes = f rZd + -Zi T r.Zl/zj + X%l. p, k-1
pmid:17247752 pmcid:PMC1209876 fatcat:rzh54poqdzcefnhuayibf34s44