Final answer:
The parent plants' genotypes were both Yy (heterozygous yellow) which resulted in 50 yellow-seed and 50 green-seed offspring, showcasing a 1:1 phenotypic ratio that can arise from such heterozygous crosses.
Step-by-step explanation:
If a cross between two pea plants produces 50 yellow-seed offspring and 50 green-seed offspring, the parental genotypes must have been heterozygous yellow (Yy) and heterozygous yellow (Yy). The reason for this assumption is that the phenotypic ratio of the offspring is 1:1, indicating that both parents contributed both dominant (yellow-seed) and recessive (green-seed) alleles. Since yellow is the dominant trait, green seeds only appear in the recessive homozygous condition (yy).
To understand the cross, we can create a Punnett square where both parents have the genotype Yy. This setup will result in the following genotypic probability: 25% YY (yellow seeds), 50% Yy (yellow seeds), and 25% yy (green seeds). However, in a phenotypic ratio, the yellow-seed (YY and Yy) offspring will be indistinguishable from each other, making the anticipated ratio of yellow to green seed offspring 3:1 in a large enough sample. Given the actual results of 50 yellow and 50 green, this particular cross may have had a smaller sample size or experienced deviation from expected ratios due to chance.