Final answer:
When Mendel crossed true breeding yellow seed plants with true breeding green seed plants, all F1 offspring exhibited yellow seeds, since yellow is the dominant trait. The correct answer is option d.
Step-by-step explanation:
When Gregor Mendel conducted his experiments with pea plants, he noted the inheritance patterns that emerged when he crossed true breeding plants with different traits. Specifically, when Mendel crossed true breeding yellow seed plants with true breeding green seed plants, he observed the resulting F1 generation offspring. Because yellow is the dominant trait for seed color in pea plants, all the offspring of such a cross between true breeding parents exhibit the yellow seed phenotype. In other words, green is a recessive trait, and it is not expressed in the presence of a dominant yellow allele.
Therefore, when answering the quiz question on seed color inheritance in this genetic cross, the correct option is that 100% of the F1 offspring would have yellow seeds. This is because the green allele is recessive and does not appear in the presence of the dominant yellow allele. A simple Punnett square analysis would confirm that if 'Y' represents the dominant yellow allele and 'y' the recessive green allele, all F1 progeny from the P generation parents (YY and yy) will have the genotype Yy, displaying the yellow seed phenotype.
Later, when F1 plants are self-fertilized or crossed with each other, Mendel found that the F2 generation exhibited a 3:1 ratio of yellow:green seeds, thereby re-expressing the recessive green phenotype in a portion of the offspring.
The correct answer to the original question is therefore: d. They would all have yellow seeds.