Mutations are :-

Options

A. Always useful
B. Mostly useful
C. Never useful
D. Rarely useful

Answer

### Step-by-Step Solution:

1. **Understanding Mutations**:
- Mutations are defined as changes in the chemical structure of genes. They can lead to alterations in the structure and function of proteins.

2. **Impact of Mutations**:
- When a mutation occurs in a gene, it can render the corresponding protein less functional or even non-functional. This indicates that mutations often have negative effects on the organism.

3. **Examples of Mutations**:
- A specific example is the point mutation in the beta-globin gene. This type of mutation can lead to less functional hemoglobin, which is detrimental to the organism.

4. **Evaluating the Options**:
- **Always Useful**: This option is incorrect because mutations are not always beneficial; they can often be harmful.
- **Mostly Useful**: This option is also incorrect, as most mutations tend to have harmful effects.
- **Never Useful**: This option is incorrect because there are instances where mutations can be beneficial.
- **Rarely Useful**: This option is correct because, while most mutations are harmful, there are rare cases where they can provide advantages, such as resistance to diseases.

5. **Conclusion**:
- Based on the analysis, the correct answer is that mutations are "rarely useful."