For selection of recombinants, insertional inactivation of antibiotic marker has been superseded by insertional inactivation of a marker gene coding for a chromogenic substrate. Give reasons.

Explanation

**Step-by-Step Solution:**

1. **Understanding Selectable Markers:**
- In genetic engineering, selectable markers are genes that provide a way to identify which cells have taken up a plasmid containing foreign DNA. Commonly used markers include antibiotic resistance genes.

2. **Traditional Method Using Antibiotic Resistance:**
- The PBR322 plasmid is a common cloning vector that contains genes for resistance to antibiotics like ampicillin and tetracycline. When foreign DNA is inserted into one of these resistance genes, it inactivates that gene.
- For example, if foreign DNA is inserted into the tetracycline resistance gene, the recombinant plasmid will lose the ability to confer tetracycline resistance.
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