Final answer:
Mendel's experiments with pea plants yielded an F2 generation phenotypic ratio of approximately 3:1, representing about 75% yellow seeds and 25% green seeds due to the dominant yellow allele and the recessive green allele.
Step-by-step explanation:
In Mendel's classic genetics experiments with pea plants, crossing a true-breeding yellow seed plant (dominant trait) with a true-breeding green seed plant (recessive trait) yields an F1 generation where all offspring display the dominant yellow seed color because they inherit one allele for yellow and one for green, making them heterozygous. When two F1 plants are crossed to produce the F2 generation, the phenotypic ratio observed is approximately 3:1, meaning approximately 75% yellow seeds to 25% green seeds. Using a Punnett square, Mendel was able to predict this outcome as the result of the segregation of alleles during gamete formation and subsequent fertilization. This demonstrates the basic principles of Mendelian inheritance, where traits are determined by discrete genes that segregate and assort independently.
The F1 offspring from a cross of true-breeding green (yy) and true-breeding yellow (YY) parents will always be heterozygous (Yy) and exhibit the yellow seed phenotype.
Subsequent self-fertilization or cross-pollination among the F1 generation (Yy x Yy) results in an F2 generation with a 3:1 phenotypic ratio of yellow to green seeds. This occurs because the allele for yellow is dominant (Y) and the allele for green is recessive (y).