Abstract
The joint segregation analysis of a mixed genetic model of major gene plus poly-gene was conducted to study the inheritance of oil content in Brassica napus L. Five populations, i.e the populations of 2 parents(P 1 and P 2), F 1, F 2 and F 2:3 (derived from F 2) family, from each of the two crosses (1141B × Ken C 1-1, 32B × Ken C 1-2) were investigated. The frequency distributions of oil content in F 2 and F 2:3 family populations show characteristics of a mixed normal distribution, which indicated that the inheritance of oil content followed a major gene plus poly-gene model. Twenty-one genetic models were established, which could be classified into five types: one and two major genes, polygenes, one and two major genes plus polygenes. The most suitable genetic model could be selected using Akaike's Information Criterion and the fitness of the selected one could be examined by a set of tests. Results show that genetic model D-2 is the most fitting genetic model for the trait. In other words, oil content in oilseed rape is controlled by one additive major gene plus additive and dominance polygenes. For cross 1 (1141B × Ken C 1-1) the heritabilities of major gene and poly-genes in F 2 are 68.21% and 27.17%, respectively, and in F 2:3 are 81.70% and 16.80%, respectively. The additive effect of major gene is–1.74, which indicates that the locus of the allele in parent 1141B may decrease the oil content, but that in parent Ken C 1-1 may increase it. The additive and dominance effects of the polygenes are 1.20 and -1.93, respectively. For cross 2 (32B × Ken C 1-2) the heritabilities of major gene and polygenes in F 2 are 66.20% and 28.10%, respectively, and in F 2:3 were 81.00% and 14.90%, respectively. The additive effect of major gene was -3.74, which also indicates that the locus of the allele in parent 32B may decrease the oil content, but that in parent Ken C 1-2 may increase it. The additive and dominance effects are -1.99 and 0.93, respectively. The heritability of the major gene in F 2:3 is higher than that in F 2 in both crosses, so it would be more efficent to conduct selection in F 2:3 families for high oil content in breeding.
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