Practice question

Phenotype of a single cross-pollinated plant poorly reflects its transmitting ability because heterozygosity, dominance, and micro-environment mask genotype. Superior appearance may result from favorable interlocus interactions or non-heritable environmental boost, not additive alleles that can be passed to progeny. Progeny testing evaluates half-sib or S1 families derived from selected plant in replicated trials, providing estimate of breeding value, general combining ability, and heritability. In recurrent selection, selected S1 plants are selfed and testcrossed to a common tester; progeny mean performance indicates whether parent carries concentration of favorable alleles affecting yield and adaptation. Without such testing, selection would favor non-heritable phenotypic deviates and genetic advance stalls. Progeny testing also distinguishes homozygous superior from heterozygous impostors, enabling accurate selection for low heritability traits where h² less than 0.3, which is typical for yield components requiring replicated evaluation. Combining ability terminology from Sprague and Tatum distinguishes general combining ability due to additive effects measured by progeny testing from specific combining ability due to dominance, guiding choice of testers and selection intensity in recurrent population improvement schemes worldwide.