Selective markers in plasmids are used to

Options

A. Identify cancer cells
B. Identify antibiotics
C. Identify recombinants from non-recombinants
D. None of these

Answer

**Step-by-Step Solution:**

1. **Understanding Selective Markers in Plasmids:**
Selective markers are genes that are introduced into plasmids to help identify which cells have taken up the plasmid containing the gene of interest. These markers typically confer resistance to antibiotics.

2. **Examples of Selective Markers:**
Common examples of selective markers include genes that provide resistance to antibiotics such as ampicillin and tetracycline. For instance, the plasmid pBR322 contains both ampicillin resistance (amp^R) and tetracycline resistance (tet^R) genes.

3. **Insertion of Gene of Interest:**
When a gene of interest is inserted into the plasmid, it often disrupts one of the selective markers. For example, if the gene of interest is inserted into the ampicillin resistance gene, the resulting recombinant plasmid will not confer ampicillin resistance.

4. **Plating on Selective Media:**
When the transformed cells (those that have taken up the plasmid) are plated on media containing ampicillin, only the cells that did not take up the recombinant plasmid (non-recombinants) will survive, as they still possess the original ampicillin resistance.

5. **Identifying Recombinants:**
The cells that have taken up the recombinant plasmid (which disrupted the ampicillin resistance) will not grow on ampicillin media. However, they can be plated on tetracycline media, where they will grow since the tetracycline resistance gene remains intact.

6. **Conclusion:**
Therefore, selective markers in plasmids are used to identify recombinants from non-recombinants by allowing the growth of only those cells that have taken up the plasmid with the gene of interest.

**Final Answer:**
Selective markers in plasmids are used to identify recombinants from non-recombinants.

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