Task

Red grain colour in wheat is determined by two pairs of polymeric (cumulative) genes: each dominant allele (A₁, A₂) adds equally to colour intensity; a₁a₁a₂a₂ grain is white. The genes are on different chromosomes. A dark-red variety (A₁A₁A₂A₂) was crossed with a white variety; F₁ was intercrossed, giving 1600 F₂ plants. 1) Explain polymery (cumulative and non-cumulative), its role in inheritance of quantitative traits, and give human examples. 2) Write the P, F₁ and F₂ crosses and group the F₂ genotypes by the number of dominant alleles. 3) Determine the F₂ phenotypic classes and their ratio. 4) Find the number of F₂ plants with two dominant alleles and their genotypes. 5) Calculate the number of F₂ plants with the phenotype of either parent. 6) Calculate the number of F₂ plants with at least one dominant allele (coloured) and the share (%) of white-grained offspring when plants with one dominant allele are test-crossed. For each part, write out the law or method used (cross scheme, formulas, reasoning) and all calculations step by step.