When both alleles of a pair are fully expressed in heterozygotes, they are called

Options

A. Lethals
B. Codominants
C. Incomplete dominants
D. Recessive allele.

Answer

To solve the question, we need to determine the correct term for when both alleles of a pair are fully expressed in heterozygotes. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Question
The question asks about a specific genetic condition where both alleles in a heterozygous organism are fully expressed. This means we are looking for a term that describes this phenomenon.

**Hint:** Think about the definitions of different types of allele interactions.

### Step 2: Review the Options
The options provided are:
1. Lethals
2. Co-dominants
3. Incomplete dominance
4. Recessive allele

**Hint:** Consider what each term means in the context of genetics.

### Step 3: Analyze Each Option
- **Lethals:** These are genes that can cause the death of an organism. This does not relate to the expression of alleles in heterozygotes, so this option is incorrect.

- **Co-dominants:** This term refers to a situation where both alleles in a heterozygote are fully expressed. For example, in blood types, both A and B alleles can be expressed in an AB blood type. This fits the description given in the question.

- **Incomplete dominance:** This occurs when the phenotype of the heterozygote is intermediate between the two homozygous phenotypes. In this case, neither allele is fully expressed, making this option incorrect.

- **Recessive allele:** A recessive allele only expresses its trait when in a homozygous recessive condition. This does not apply to the situation described in the question, so this option is also incorrect.

**Hint:** Identify which option aligns with the definition of fully expressed alleles in heterozygotes.

### Step 4: Conclusion
Based on the analysis, the correct answer is **co-dominants**. This term accurately describes the condition where both alleles are fully expressed in a heterozygote.

**Final Answer:** Co-dominants