Final answer:
The F1 cross of two heterozygous pea plants (RrYy) will yield a phenotypic ratio of 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green peas in the F2 generation, as determined by a forked-line or branched diagram for independent assortment.
Step-by-step explanation:
The question involves a genetic cross between pea plants with different traits. The parent generation had round yellow peas and green wrinkled peas. According to Mendelian genetics, round seed shape (R) is dominant to wrinkled seed shape (r), and yellow color (Y) is dominant to green color (y). Therefore, the F1 generation all displayed the dominant phenotypes: round seeds with yellow leaves.
To find the phenotypic ratio of the cross between the F1 generation, we can use a forked-line or branched diagram. Since all F1 individuals have round yellow peas, their genotype must be RrYy (heterozygous for both traits). When these F1 plants are crossed with each other, the phenotypic ratio of their offspring (F2 generation) will be 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green.
This 9:3:3:1 ratio is arrived at by multiplying the probabilities of independent assortment for each trait (3 round : 1 wrinkled from the R/r allele and 3 yellow : 1 green from the Y/y allele). Using the branch diagram method, we take each trait separately to determine the probability of phenotypes for that trait, and then multiply these together to obtain the combined phenotypic ratio for both traits.