Answer:
C. The green allele is recessive to the yellow allele
Explanation:
Complete dominance occurs when one gene variant or allele referred to as the 'dominant allele' completely masks the expression of another allele referred to as the 'recessive allele' in heterozygous individuals, i.e., in individuals carrying one copy of the dominant allele and one copy of the recessive allele for a particular locus/gene (whereas homo-zygous individuals carry the same alleles for a given locus/gene). Mendel crossed pure lines of pea plants, i.e., homo-zygous lines for different traits such as seed color (yellow and green) and seed shape (round and wrinkled). In this case, the parental cross was YY x yy, where the 'Y' allele is dominant and encodes for yellow seed color, and the 'y' allele is recessive and encodes for green seed color. From this cross, Mendel obtained a hybrid F1 (i.e., all progeny was heterozygous with genotype Yy). An expected 3:1 ratio as observed in this case (6,022 yellow and 2,001 green seed >> 3:1 ratio) is characteristic of the progeny that results from mating between F1 heterozygous parents, where each parent has one dominant allele and one recessive allele, i.e., F1 parental cross: Yy x Yy >> F2: 1/4 YY (yellow color); 1/2 Yy (yellow color); 1/4 (green color) >> 3:1 ratio of yellow to green seeds.
