Epistasis implies

Options

A. One pair of genes can completely mask the expression of another pair of genes
B. One pair of genes independently controls a particular phenotype
C. One pair of genes enhances the phenotypic expression of another pair of genes
D. Many genes collectively control a particular phenotype

Answer

### Step-by-Step Solution:

1. **Understanding Epistasis**:
- Epistasis is a genetic phenomenon where the expression of one gene is completely masked by another gene. This means that the presence of one gene can inhibit or suppress the effects of another gene.

2. **Identifying the Options**:
- The question provides four options regarding what epistasis implies:
- A) One pair of genes can completely mask the expression of another pair of genes.
- B) One pair of genes independently controls a particular phenotype.
- C) One pair of genes enhances the phenotypic expression of another pair of genes.
- D) Many genes collectively control a particular phenotype.

3. **Analyzing the Correct Option**:
- Based on the definition of epistasis, option A is correct because it directly states that one pair of genes can completely mask the expression of another pair of genes. This aligns with the definition of epistasis.

4. **Providing an Example**:
- An example of epistasis is the coat color in mice, where one gene (C) can mask the effects of another gene (B). If the gene C is in a homozygous recessive state (cc), it results in a white coat regardless of the genotype of gene B.

5. **Conclusion**:
- Therefore, the answer to the question is option A: "One pair of genes can completely mask the expression of another pair of genes."