$ Those two pairs of genes which if present in dominant stage, do not produce any expression but when present collectively in dominant stage, produce a phenotypic expression are called complementory genes.
! Inheritance of purple flower colour in Pea gives a phenotypic ratio of 9:7, as a result of selfing of F-1 -offsprings.

Options

A. If both As and R are correct and R is correct explanation of As
B. If both As and R are correct but R is not correct explanation of As
C. If As is correct, R is wrong
D. If both As and R are wrong.

Answer

To solve the question regarding complementary genes and the inheritance of purple flower color in pea plants, we will follow a step-by-step approach.

### Step 1: Understand the Concept of Complementary Genes
Complementary genes are defined as two pairs of genes that do not express a phenotype when present individually in their dominant forms. However, when both pairs are present together in their dominant forms, they produce a specific phenotypic expression.

**Hint:** Remember that complementary genes require interaction between different genes to express a trait.

### Step 2: Analyze the Assertion
The assertion states that those two pairs of genes, when present in dominant stage, do not produce any expression but collectively produce a phenotypic expression. This aligns with the concept of complementary genes.

**Hint:** Focus on how the interaction of genes is necessary for the expression of a trait.

### Step 3: Understand the Example of Purple Flower Color in Peas
The reason given in the question refers to the inheritance of purple flower color in pea plants, which follows a phenotypic ratio of 9:7 when F1 offspring are selfed. This indicates that two genes are involved in determining the flower color.

**Hint:** Look for the relationship between the genes and the resulting flower color ratio.

### Step 4: Identify the Genes Involved
In the case of purple flower color, let’s denote the two genes as:
- Gene 1: C (dominant) and c (recessive)
- Gene 2: P (dominant) and p (recessive)

When both dominant alleles (C and P) are present, the phenotype is purple flowers. If either gene is present in its recessive form (cc or pp), the flowers will be white.

**Hint:** Consider how the presence of dominant and recessive alleles affects the phenotype.

### Step 5: Determine the F2 Generation Ratio
When F1 plants (all purple flowers) are selfed, the resulting F2 generation shows a phenotypic ratio of 9 purple flowers to 7 white flowers. This is indicative of complementary gene action, as both dominant alleles must be present for the purple phenotype to be expressed.

**Hint:** Remember that the ratio reflects the interaction of the two genes.

### Step 6: Conclusion
Both the assertion and the reason are correct. The assertion accurately describes complementary genes, and the reason provides a specific example of how these genes interact in pea plants to produce a 9:7 phenotypic ratio. However, the reason does not directly explain the assertion; they are related but not causally linked.

**Hint:** Distinguish between correlation and causation in genetic explanations.

### Final Answer
Both the assertion (A) and the reason (R) are correct, but R is not the correct explanation of A.