Abstract
A biometrical genetic model is presented for the testcross performance of genotypes derived from a cross between two pure-breeding lines. The model is applied to obtain the genetical expectations of first and second degree statistics of testcrosses established from F2, first and higher backcross populations and their selfing generations. Theoretically, the testcross mean of these populations is expected to be a linear function of the percentage of germplasm from each parent line in the absence of epistasis. In both F2 and backcross populations, the new arising testcross variance between sublines is halved with each additional generation of selfing. Special consideration is given to the effects of linkage and epistasis, and tests for their presence are provided. The results are discussed with respect to implications in “second cycle” breeding. It is concluded that the choice of base populations between F2 and first backcrosses can be made on the distributions of testcrosses from the first segregating generation. Schnell's (1983) “usefulness” criterion is recommended for choosing the optimum type of base population.
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Melchinger, A. Expectation of means and variances of testcrosses produced from from F2 and backcross individuals and their selfed progenies. Heredity 59, 105–115 (1987). https://doi.org/10.1038/hdy.1987.101
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DOI: https://doi.org/10.1038/hdy.1987.101
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