Practice question

Mass selection operates directly on visible phenotypic values of individual plants in a population. Breeder walks field, visually scores traits such as plant height, earliness, seed color, or disease-free appearance, and harvests seeds from best looking individuals to constitute next generation bulk. Underlying genotype is not tested through progeny rows, molecular markers, or combining ability assays. Success depends on high heritability where phenotype mirrors additive genetic value, correlation between observable character and breeding value, and low environmental noise. It is simplest breeding method practiced since domestication, requiring no controlled crosses or pedigree books. However, it cannot distinguish homozygous PP from heterozygous Pp if dominance conceals recessive allele, and is confounded by macro-environmental variation across field blocks. Modification with stratification or selection of many individuals and progeny testing improves its genetic gain for low heritability characters. Heritability and selection intensity determine response to mass selection; high heritability traits like plant height respond quickly, whereas low heritability yield traits require stratified mass selection or honeycomb designs to reduce environmental variance and improve accuracy.