In case of inheritance of one gene, `3:1` phenotypic ratio can be explained on the basis of-

Options

A. Incomplete dominance
B. Codominance
C. Dominance
D. Linkage

Answer

To explain the 3:1 phenotypic ratio in the inheritance of one gene, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Basics of Genetics**:
- Genes exist in pairs, with one allele being dominant and the other recessive. The dominant allele will express its trait over the recessive allele.

2. **Identifying the Cross**:
- When we perform a monohybrid cross (a cross between two individuals that differ in one trait), we can use the classic example of pea plants where one trait is dominant (e.g., purple flowers) and the other is recessive (e.g., white flowers).

3. **F1 Generation**:
- In the first generation (F1), when a homozygous dominant (PP) is crossed with a homozygous recessive (pp), all offspring will be heterozygous (Pp) and exhibit the dominant phenotype (purple flowers).

4. **F2 Generation**:
- When the F1 generation (Pp) is self-crossed (Pp x Pp), we can use a Punnett square to determine the genotypes of the offspring in the F2 generation. The possible combinations will be:
- PP (homozygous dominant)
- Pp (heterozygous)
- pp (homozygous recessive)

5. **Calculating the Ratios**:
- The genotypic ratio from the Punnett square will be:
- 1 PP : 2 Pp : 1 pp
- When we look at the phenotypes, both PP and Pp will express the dominant phenotype (purple flowers), while pp will express the recessive phenotype (white flowers). Thus, the phenotypic ratio becomes:
- 3 (dominant) : 1 (recessive)

6. **Conclusion**:
- Therefore, the 3:1 phenotypic ratio can be explained by the principle of dominance, where the dominant allele masks the effect of the recessive allele in the heterozygous condition.

### Final Answer:
The 3:1 phenotypic ratio in the inheritance of one gene can be explained on the basis of **dominance**.

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