Expression of a recessive phenotype in a deletion heterozygote is due to:

Options

A. Pseudo-dominance
B. partial-dominance
C. super-dominance
D. co-dominance

Answer

### Step-by-Step Solution:

1. **Understand the Terms**:
- **Recessive Phenotype**: A phenotype that is expressed only when an individual has two copies of the recessive allele (homozygous recessive).
- **Deletion Heterozygote**: An individual that has one normal allele and one allele that has undergone a deletion, resulting in a loss of genetic material.

2. **Identify the Mechanism**:
- In a deletion heterozygote, the presence of a deletion can lead to the expression of a recessive phenotype. This occurs because the normal allele may not be able to compensate for the missing function of the deleted allele.

3. **Concept of Pseudodominance**:
- Pseudodominance refers to the phenomenon where a recessive trait appears to be dominant due to the deletion of the dominant allele or part of its function. In this case, the recessive phenotype is expressed because the dominant allele is either absent or non-functional.

4. **Evaluate Other Options**:
- **Partial Dominance**: This involves a blending of traits and does not apply to the expression of a recessive phenotype in a deletion heterozygote.
- **Super Dominance**: This refers to a situation where the phenotype of the heterozygote is more extreme than either homozygote, which is not relevant here.
- **Co-dominance**: This occurs when both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits distinctly. This does not lead to the expression of a recessive phenotype.

5. **Conclusion**:
- The expression of a recessive phenotype in a deletion heterozygote is primarily due to **pseudodominance**. This is because the deletion of the dominant allele allows the recessive trait to be expressed.

### Final Answer:
The expression of a recessive phenotype in a deletion heterozygote is due to **pseudodominance**.

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