Practice question

Because mass selection avoids intensive inbreeding and retains many selected parents bulked together, resulting population preserves substantial genetic diversity and heterozygosity buffer. Broad base of alleles confers buffering against diverse environmental stresses, disease races, and climatic fluctuations, granting stable performance across years and locations. Unlike pure lines that may fail in off-type environments, mass-selected varieties contain mixture of genotypes complementary in stress tolerance, maintaining yield stability due to population buffering mechanism described by Allard. Historically, landraces developed by farmer mass selection in centers of diversity exhibit wide adaptation and resilience to marginal soils. Method also conserves rare minor genes and polygenic complexes underlying local adaptation. Low cost, no need for controlled pollination, and maintenance of variability make it attractive for low-input traditional systems and for initial improvement before advanced pedigree programs requiring purity. Heterogeneous populations also exhibit compensatory growth where different genotypes fill gaps, maintain canopy closure, reduce weed invasion, and provide insurance against complete crop failure under unpredictable monsoon variability common in traditional farming systems and marginal environments.