The phenotypic ratio in F2 generation of a monohybrid self-cross is
Selfing heterozygous F1 Tt generates gametic pool with equal frequencies of T and t from each parent. Punnett square combining maternal and paternal gametes yields three genotypic classes TT 25 percent, Tt 50 percent and tt 25 percent. With complete dominance dominance masks heterozygote, tall phenotype encompasses TT plus Tt totaling 75 percent, dwarf tt 25 percent, giving phenotypic ratio 3 tall to 1 dwarf. Genotypic ratio 1:2:1 differs from phenotypic count, 1:1 and 9:3:3:1 correspond to test cross and dihybrid respectively. Cytological correlation with prophase pairing, metaphase alignment
Ref: Snustad & Simmons, Principles of Genetics, 7th ed., Chapter 3: F2 Phenotypic Ratio
