In sweet pea, the epistatic interaction between the genes for purple and white colour produced the two colours in the ratio

Options

A. `3:1 `
B. `8:8`
C. `9:3:3:1`
D. `9:7`

Answer

To solve the question regarding the epistatic interaction between the genes for purple and white color in sweet pea, we need to understand the concept of epistasis and how it affects the phenotypic ratios in genetic crosses.

### Step-by-Step Solution:

1. **Understand Epistasis**: Epistasis occurs when the expression of one gene is affected by another gene. In this case, we have two genes controlling flower color in sweet pea: one for purple color (let's denote it as P) and one for white color (denote it as W).

2. **Identify the Alleles**:
- Let’s assume that the allele for purple flowers (P) is dominant over the allele for white flowers (p).
- Similarly, let’s assume that the allele for the second gene (W) is also dominant over the recessive allele (w).

3. **Determine the Cross**:
- If we cross a homozygous purple flower (PP) with a homozygous white flower (pp), all offspring will be heterozygous (Pp) and display the purple phenotype.
- However, if we consider a situation where one gene (for example, the one for white color) is epistatic to the other, it can mask the expression of the other gene.

4. **Analyze the Ratios**:
- In a typical dihybrid cross involving epistasis, the phenotypic ratio can be different from the expected 9:3:3:1 ratio of a standard dihybrid cross.
- For sweet pea, the interaction between the genes for purple and white color can lead to a ratio of 12:3:1, where:
- 12 represents the purple flowers (both dominant alleles present),
- 3 represents the white flowers (one dominant and one recessive allele),
- 1 represents the absence of color (both recessive alleles).

5. **Conclusion**: Therefore, the epistatic interaction between the genes for purple and white color in sweet pea produces the two colors in the ratio of **12:3:1**.