A pea with white flowers was crossed to another pea which is also white flower plant. When selfed the `F_(2)` generation produced purple and white in the ration 9:7. The reason for the results is that

Options

A. It is typical monohybrid Mendalian ratio
B. Purple flower colour is dominant over the white
C. It is a complementary factor
D. None of the above

Answer

To solve the problem, we need to analyze the genetic basis of the flower color in pea plants and understand the inheritance pattern that leads to the observed phenotypic ratio in the F2 generation.

### Step-by-Step Solution:

1. **Identify the Parental Generation**:
- We start with two pea plants that both have white flowers. Let's denote the flower color gene as "P" for purple (dominant) and "p" for white (recessive).

2. **Determine the Genotype of the Parents**:
- Since both parents have white flowers, they can be either homozygous recessive (pp) or heterozygous (Pp). However, since they produce an F2 generation with a 9:7 ratio, we can infer that they are likely homozygous recessive (pp).

3. **Cross the Parental Generation**:
- When these two white flower plants (pp) are crossed, they produce F1 offspring. Since both parents are pp, all F1 offspring will also be pp (white flowers).

4. **Selfing the F1 Generation**:
- When the F1 generation (pp) is selfed, we would expect the F2 generation to also be pp, resulting in all white flowers. However, the problem states that the F2 generation produced a 9:7 ratio of purple to white flowers.

5. **Understanding the 9:7 Ratio**:
- The 9:7 ratio suggests that there are two genes involved in determining flower color, which interact in a complementary manner. This means that two different genes (let's call them A and B) are required for the expression of the purple flower phenotype.
- The presence of at least one dominant allele from both genes (A and B) is necessary to produce purple flowers. If either gene is homozygous recessive (aa or bb), the flower will be white.

6. **Genotypic Ratio**:
- The genotypes leading to the observed phenotypes can be represented as follows:
- A_B_ (purple) = 9
- A_bb (white) = 3
- aaB_ (white) = 3
- aabb (white) = 1
- This results in a total of 9 purple flowers and 7 white flowers.

7. **Conclusion**:
- The reason for the 9:7 ratio is due to the interaction of two complementary genes that control flower color in pea plants. The presence of both dominant alleles is necessary for the expression of purple flowers, while the absence of either leads to white flowers.

### Final Answer:
The reason for the results is that the flower color in pea plants is controlled by two complementary genes, leading to a 9:7 ratio of purple to white flowers in the F2 generation.