Practice question

Quantitative inheritance produces continuous distribution influenced by multiple loci and environment. Traits such as total biomass, grain yield, tiller number, seed number per inflorescence, and harvest index depend on additive effects of polygenes controlling photosynthesis, assimilate partitioning, and reproductive efficiency. Somaclonal variation that perturbs phytohormone homeostasis or minor regulatory genes often generates incremental shifts rather than novel discrete phenotypes. Evaluation requires replicated randomized blocks, measurement with balances and counters, and statistical analysis of variance to separate genetic change from environmental fluctuation. Heritability estimates tend to be moderate to low. Breeders track yield components because slight reductions indicate somaclonal deterioration affecting economic performance. Hence classification of yield and seed number as quantitative characters accurately reflects their polygenic control, continuous range, and sensitivity to tissue culture induced minor gene mutations accumulated over subcultures. Genomic regions controlling quantitative traits identified through QTL mapping show small additive effects distributed across chromosomes. Somaclonal variation may disrupt these QTLs via minor insertions or methylation changes, causing measurable yield depression. Hence precise phenotyping over seasons remains essential to quantify continuous variation and guide selection for agronomically superior somaclones.