True-breeding female gametes homozygous recessive PHENOTYPES parent plant 當 True-breeding homozygous dominant Aa Aa Figure 11.6 Punnett-square method of predicting the probable outcome of a genetic cross. Circles represent gametes. Italic letters on the gametes represent dominant or recessive alleles. The differer squares show the different genotypes possible among offspring. In 学<-学 this case, gametes are from a self-fertilizing heterozygous(Aa)plant. ae Figure 11.7 (Right) Results from one of Mendel's monohybrid crosses. On average. the dominant-to- recessive ratio among An F, plant the second-generation(F2) plants was 3: 1.Fa self-fertilizes and produces PHENOTYPES gametes To Mendel, the ratio suggested that fertilization is a chance event, with a number of possible outcomes And he had an understanding of probability, which applies to chance events and therefore could help him predict the possible outcomes of crosses. Probability simply means this: The chance that each outcome of a given event will occur is proportional to the number of ways it can be 曾 reached Aa用a3 The Punnett-square method, explained in Figure 11.6