Genetic diagnosis by DNA testing:

Options

A. detects only mutant and normal alleles
B. can be done only on eggs or sperms
C. involves hybridisation to ribosomal RNA
D. utilises restriction enzymes and polymorphic site

Answer

### Step-by-Step Solution:

1. **Understanding Genetic Diagnosis**: Genetic diagnosis involves identifying genetic disorders through various testing methods, primarily DNA testing. This process helps in detecting mutations or abnormalities in genes that may lead to genetic diseases.

2. **Types of Genetic Testing**: There are different types of genetic testing, including:
- **Carrier Testing**: Determines if an individual carries a gene for a specific genetic disorder.
- **Prenatal Testing**: Tests the fetus for genetic disorders before birth.
- **Newborn Screening**: Tests for genetic disorders shortly after birth.
- **Preimplantation Genetic Diagnosis (PGD)**: Conducted during in vitro fertilization (IVF) to screen embryos for genetic conditions before implantation.

3. **Analyzing the Options**:
- **Option 1**: "Detects only mutant and normal alleles" - This is partially true but does not encompass the full scope of genetic testing.
- **Option 2**: "Can be done only on eggs or sperms" - This statement is accurate in the context of preimplantation genetic diagnosis, which is performed on embryos created from eggs and sperm during IVF.
- **Option 3**: "Immunization to ribosomal RNA" - This is unrelated to genetic diagnosis.
- **Option 4**: "Utilization restriction enzymes and polymorphic site" - While restriction enzymes are used in some genetic testing methods, this statement does not specifically pertain to the overall concept of genetic diagnosis.

4. **Conclusion**: Based on the analysis, the most accurate statement regarding genetic diagnosis by DNA testing is that it "can be done only on eggs or sperms," particularly in the context of preimplantation genetic diagnosis during in vitro fertilization.

### Final Answer:
The correct answer is **Option 2**: "Can be done only on eggs or sperms."

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