Three strains of green-seeded lentil plants appear to have the same phenotype. The strains are designated G₁, G₂, and G₃. Each green-seeded strain is crossed to a pure-breeding yellow-seeded strain designated Y. The F₁ of each cross are yellow; however, self-fertilization of F₁ plants produces F₂ with different proportions of yellow- and green-seeded plants as shown below.

For each set of F₂ progeny, provide a genetic explanation for the yellow : green ratio. What are the genotypes of yellow and green F₂ lentil plants in the G₂ x Y cross? 

Verified step by step guidance

1. Step 1: Understand the parental genotypes and phenotypes. The green-seeded strains G₁, G₂, and G₃ are crossed with a pure-breeding yellow-seeded strain Y. Since all F₁ progeny are yellow, yellow is dominant over green.
2. Step 2: Analyze the F₂ phenotypic ratios for each cross. For G₂ x Y, the F₂ ratio is 7 green : 9 yellow (or 7/16 green and 9/16 yellow). This ratio suggests that more than one gene is involved in determining seed color, indicating a dihybrid interaction rather than a simple monohybrid.
3. Step 3: Propose a genetic model for G₂ x Y. Since the F₂ ratio deviates from the classic 3:1, consider two genes with dominant and recessive alleles interacting. The yellow phenotype likely requires at least one dominant allele at both loci, while green appears when recessive alleles are present at either or both loci.
4. Step 4: Assign genotypes to the parental strains based on the F₂ ratio. The pure-breeding yellow strain Y would be homozygous dominant at both loci (e.g., AABB). The green strain G₂ would be homozygous recessive at one locus and homozygous dominant at the other (e.g., aaBB or AAbb), leading to the observed 9:7 ratio in F₂.
5. Step 5: Determine the genotypes of yellow and green F₂ plants in the G₂ x Y cross. Yellow F₂ plants have at least one dominant allele at both loci (A_B_), while green F₂ plants are homozygous recessive at one or both loci (aaB_, Aabb, or aabb). This explains the 9:7 phenotypic ratio observed.

Key Concepts

Mendelian Inheritance and Dominance

Mendelian inheritance explains how traits are passed from parents to offspring through dominant and recessive alleles. In this question, yellow seed color is dominant over green, as all F1 progeny are yellow. Understanding dominance helps predict phenotypic ratios in F2 generations.

Genotypic Ratios and Punnett Squares

Genotypic ratios describe the distribution of different allele combinations in offspring. Punnett squares are tools to visualize these combinations and predict phenotypic ratios. The varying F2 ratios suggest different genetic mechanisms or allele interactions in each green strain crossed with yellow.

Complementation and Multiple Alleles

Complementation occurs when mutations in different genes produce the same phenotype but restore normal function when combined. The different F2 ratios imply that green seed color in G1, G2, and G3 may result from mutations in different genes or alleles, affecting segregation patterns and phenotypic ratios.