In the `F_(2)` generation, genotypic and phenotypic ratios are identical in case of

Options

A. Complementary genes
B. Mendelian dihybrids
C. Mendelian monohybrids
D. Incomplete dominance

Answer

To solve the question regarding the genotypic and phenotypic ratios in the F2 generation, we will analyze the options provided and understand the concept of incomplete dominance.

### Step-by-Step Solution:

1. **Understanding the Terms**:
- Genotypic ratio refers to the ratio of different genotypes produced in the offspring.
- Phenotypic ratio refers to the ratio of different phenotypes (observable traits) produced in the offspring.

2. **Identifying the Options**:
- The options given are:
- A) Complementary genes
- B) Mendelian dihybrids
- C) Mendelian monohybrids
- D) Incomplete dominance

3. **Analyzing Incomplete Dominance**:
- In incomplete dominance, the phenotype of the heterozygous genotype is an intermediate of the two homozygous phenotypes.
- For example, in snapdragon flowers, if red (RR) and white (rr) flowers are crossed, the F1 generation will be all pink (Rr).
- When these F1 individuals (Rr) are crossed, the F2 generation will have a phenotypic ratio of 1 red: 2 pink: 1 white, which is also the same as the genotypic ratio (1 RR: 2 Rr: 1 rr).

4. **Comparing Other Options**:
- **Mendelian dihybrids**: In a dihybrid cross, the phenotypic ratio is typically 9:3:3:1, which is different from the genotypic ratio.
- **Mendelian monohybrids**: In a typical monohybrid cross, the phenotypic ratio is 3:1, which does not match the genotypic ratio of 1:2:1.
- **Complementary genes**: This concept also does not yield identical genotypic and phenotypic ratios.

5. **Conclusion**:
- The only scenario where the genotypic and phenotypic ratios are identical in the F2 generation is in the case of **incomplete dominance**.

### Final Answer:
The correct answer is **D) Incomplete dominance**.