Abstract
Three random samples of inbred lines, two (B and D) extracted from the V1 × V5 and V2 × V12 crosses of Nicotianarustica and the third (Dc) produced from their double cross (V1×V5)×(V2×V12), have been compared for seven quantitative characters. Theoretically, the genetical expectations of the first, second, third and fourth order statistics of these samples are expected to differ both in the absence and presence of complications like epistasis, linkage disequilibrium and genotype × environmental interactions. However, the magnitudes of these differences depend largely on the numbers of loci (kb1 and kb2) that segregate in the single crosses and on the background loci (kf) that have different alleles fixed in each pair of parents. In practice, the statistics and distributions of B, D and Dc samples differ significantly from each other for most of the characters. The statistics of the Dc sample, on the other hand, have values that often lie between those of B and D samples. In fact the statistical properties of the Dc sample are adequately mimicked by the joint distribution of the B + D inbreds except for range and intertrait correlations.
Further, the extreme recombinant inbreds from the double cross sample are not generally superior to those from the B and D samples. However, they do cover between 88 per cent to 109 per cent of the total range that is jointly covered by the extreme inbreds of the B and D samples. Theoretically the double cross is a better source when almost all of the genetic variability is contributed by the background loci (kf) and the alleles are dispersed between the two pairs of parents.
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Pooni, H., Jinks, J. & Yohannes, D. Comparison of inbred lines extracted from two single crosses and their double cross by single seed descent. Heredity 56, 263–276 (1986). https://doi.org/10.1038/hdy.1986.39
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DOI: https://doi.org/10.1038/hdy.1986.39
