The colonies of recombinant bacteria appear white in contrast to blue colonies of non-recombinant bacteria because of

Options

A. Insertional inactivation of alpha - galactosidase in non-recombinant bacteria
B. Insertional inactivation of alpha - galactosidase in recombinant bacteria
C. Inactivation of glycosidase enzyme in recombinant bacteria
D. Non-recombinant bacteria containing beta-galactosidase

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: The question asks why recombinant bacteria appear white while non-recombinant bacteria appear blue. This is related to a common method used in molecular biology for screening transformed bacteria.

2. **Role of the LacZ Gene**: In the plasmid vector used for transformation, there is a gene called LacZ that encodes the enzyme beta-galactosidase (not alpha-galactosidase as mentioned in the transcript). This enzyme is responsible for breaking down X-gal, a substrate that produces a blue color when cleaved.

3. **Insertion of Foreign DNA**: When foreign DNA is inserted into the plasmid, it can disrupt the LacZ gene. If the foreign DNA is inserted into the LacZ gene, the gene becomes inactive, and beta-galactosidase is not produced.

4. **Colony Color Differences**:
- **Recombinant Bacteria**: If the plasmid contains the foreign DNA, the LacZ gene is disrupted, and the bacteria cannot produce beta-galactosidase. As a result, when these bacteria grow on a medium containing X-gal, they do not produce the blue color, leading to the formation of white colonies.
- **Non-Recombinant Bacteria**: If the plasmid does not contain any foreign DNA, the LacZ gene remains intact, and the bacteria produce beta-galactosidase. These bacteria will cleave X-gal, resulting in blue colonies.

5. **Conclusion**: The white colonies indicate the presence of recombinant bacteria (with disrupted LacZ gene), while the blue colonies indicate non-recombinant bacteria (with intact LacZ gene).

**Final Answer**: The colonies of recombinant bacteria appear white in contrast to blue colonies of non-recombinant bacteria because the insertion of foreign DNA disrupts the LacZ gene, preventing the production of beta-galactosidase, which is responsible for the blue color.

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