Practice question

Classical Mendelian dihybrid experiment crossed peas differing in two traits such as seed color Yy and shape Rr. F1 heterozygotes YyRr selfed produce gametes YR, Yr, yR, yr equally. Random union yields F2 phenotypic distribution 9 Y-R- both dominant, 3 Y-rr one dominant, 3 yyR- other dominant, 1 yyrr double recessive. This 9:3:3:1 ratio equals product of two independent 3:1 monohybrid ratios, signifying independent assortment of unlinked genes with complete dominance. Any significant distortion suggests linkage creating parental excess or epistasis collapsing classes, making ratio reference standard.