Carrier organism refers to an individual which carries a

Options

A. recessive gene that is not expressed
B. dominant gene tht is not expressed
C. recessive gene that is expressed
D. dominant gene which is expressed

Answer

### Step-by-Step Solution:

1. **Understanding the Terminology**:
- A carrier organism is defined as an individual that carries a gene for a particular trait or disease but does not exhibit the trait or disease itself.

2. **Identifying Gene Types**:
- Genes can be dominant or recessive. Dominant genes express their traits even if only one copy is present, while recessive genes require two copies (one from each parent) to express their traits.

3. **Evaluating the Options**:
- **Option 1**: Recessive gene that is not expressed.
- **Option 2**: Dominant gene that is not expressed.
- **Option 3**: Recessive gene that is expressed.
- **Option 4**: Dominant gene which is expressed.

4. **Analyzing Each Option**:
- **Option 2 and Option 4** are incorrect because dominant genes will always express their traits if present.
- **Option 3** is incorrect as it refers to a recessive gene that is expressed, which contradicts the definition of a carrier.
- **Option 1** is correct because it describes a carrier organism as one that possesses a recessive gene that does not manifest phenotypically due to the presence of a dominant allele.

5. **Conclusion**:
- Therefore, the correct answer is that a carrier organism refers to an individual which carries a recessive gene that is not expressed.