Abstract
The phenotypic and genotypic properties of second cycle hybrids are predicted from the means and variances of the F2 generation of two crosses between pairs of inbred varieties of Nicotiana rustica (V1 × V5 and V2 × V12). The predicted properties are compared with the observed properties of the second cycle hybrids generated by crossing the first cycle recombinant inbred lines with the F1 of the original cross (the L3 generation of an inbred line triple test cross) which, in the absence of a linkage disequilibrium, are identical with the second cycle hybrids produced as a diallel set of crosses among the first cycle inbred lines. In the presence of a linkage disequilibrium the diallel set of crosses has a smaller linkage bias than the inbred line × F1 crosses.
The agreement between the predicted and observed phenotypic properties of the second cycle hybrids is good over a wide range of characters in both crosses. The overall correlations between the observed and expected proportions are 0·81 and 0·88 for the V1 × V5 and V2 × V12 crosses, respectively. Furthermore, the genotypic predictions show that only few of the second cycle hybrids and second cycle inbred lines will be superior to the best first cycle inbred lines which were themselves superior to their own better parents and their heterotic F1's.
Genetical explanations of the origins of the superior derivatives of an initial cross are explored using a development of the standard notation of Mather and Jinks (1982).
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Pooni, H., Jinks, J. & de Toledo, J. Predicting and observing the properties of second cycle hybrids using basic generations and inbred line × F1 crosses. Heredity 54, 121–129 (1985). https://doi.org/10.1038/hdy.1985.16
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DOI: https://doi.org/10.1038/hdy.1985.16
