Mendel’s monohybrid ratio (3:1) is a result of
Mendel's monohybrid phenotypic ratio 3:1 emerges because F1 heterozygote produces equal numbers of gametes carrying dominant and recessive alleles following homologous segregation in meiosis I. Random fusion of these two gamete types from both parents gives F2 genotypes TT 25 percent, Tt 50 percent and tt 25 percent, collapsing to three quarters dominant phenotype and one quarter recessive under complete dominance. Independent assortment influences dihybrid ratios, random fertilisation alone insufficient without prior segregation, mutation irrelevant to ratio generation itself. Understanding this mechanism aids pedigree analysis, Punnett predictions, linkage mapping and appreciating evolutionary conservation across taxa.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 2: 3:1 Ratio Explanation