Which of the following are correct?
a) PCRs are defined as the organisms, which carry foreign genes
b) SCID is a group of rare genetic disorders
c) Cloning is the production of GMOs, eg, Flavr-savr tomato
d) The bacteria use restriction endonucleases to destroy the DNA of invading foreign viruses

Options

A. a, b & c are correct
B. a & b are correct
C. b & d are correct
D. a & c are correct

Answer

To determine which statements are correct, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement a**: "PCRs are defined as the organisms, which carry foreign genes."
- **Analysis**: This statement is incorrect. PCR (Polymerase Chain Reaction) is not an organism; it is a technique used to amplify (make multiple copies of) DNA. Therefore, this statement is false.

2. **Statement b**: "SCID is a group of rare genetic disorders."
- **Analysis**: This statement is correct. SCID stands for Severe Combined Immunodeficiency, which is indeed a group of rare genetic disorders caused by mutations that affect the immune system. This statement is true.

3. **Statement c**: "Cloning is the production of GMOs, e.g., Flavr Savr tomato."
- **Analysis**: This statement is incorrect. Cloning refers to the process of making identical copies of an organism, while GMOs (Genetically Modified Organisms) involve altering the genetic material of an organism to introduce new traits. The Flavr Savr tomato is an example of a GMO, but cloning and genetic modification are different processes. Therefore, this statement is false.

4. **Statement d**: "The bacteria use restriction endonucleases to destroy the DNA of invading foreign viruses."
- **Analysis**: This statement is correct. Bacteria use restriction endonucleases as a defense mechanism against invading viruses (bacteriophages) by cutting the viral DNA, thus preventing the virus from replicating. This statement is true.

### Conclusion:
Based on the analysis:
- **Correct Statements**: b) and d)
- **Incorrect Statements**: a) and c)

Therefore, the correct answer is that statements **b** and **d** are correct.