When both alleles express their effect on being present together, the phenomenon is called

Options

A. Co-dominance
B. Dominance
C. Incomplete dominance
D. Pseudodominance

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about a genetic phenomenon where both alleles express their effects when present together.

2. **Identifying Key Terms**:
- Alleles: Different forms of a gene.
- Expressing effects: This means that the traits associated with both alleles are visible in the phenotype.

3. **Exploring Genetic Concepts**:
- **Co-dominance**: This is a genetic scenario where both alleles in a heterozygous individual fully express themselves. An example is the ABO blood group system, where both A and B alleles are expressed in individuals with AB blood type.
- **Dominance**: In this case, one allele masks the effect of another. Only the dominant trait is expressed.
- **Incomplete dominance**: Here, neither allele is completely dominant, resulting in a blend of traits (e.g., red and white flowers producing pink flowers).
- **Pseudo dominance**: This refers to a situation where a recessive trait appears to be dominant due to the absence of the dominant allele.

4. **Conclusion**: Based on the definitions and examples, the correct answer to the question is **co-dominance**, as it specifically describes the situation where both alleles express their effects simultaneously.

**Final Answer**: The phenomenon is called **co-dominance**.

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