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

Options

A. lnsertional inactivation of alphagalac- tosidase in recombinant bacteria
B. Inactivation of glycosidase enzyme in recombinant bacteria
C. Non-recombinant bacteria containing beta- galactosidase
D. insertional inactivation of alphagalac- tosidase in non-recombinant bacteria

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: The question is about the difference in color between recombinant and non-recombinant bacteria. This is a common method used in molecular biology known as blue-white screening.

2. **Identifying the Mechanism**: The blue-white screening technique is used to differentiate between bacteria that have taken up a plasmid with a foreign DNA insert (recombinant) and those that have not (non-recombinant).

3. **Role of the LacZ Gene**: The plasmid used in this process contains the LacZ gene, which encodes the enzyme beta-galactosidase. This enzyme is responsible for breaking down lactose and its analogs.

4. **Effect of Foreign DNA Insertion**: When foreign DNA is inserted into the LacZ gene, it disrupts the gene's function. This is referred to as "insertional inactivation." As a result, the bacteria with the recombinant plasmid do not produce beta-galactosidase.

5. **Interaction with X-gal**: X-gal is a colorless compound that is a substrate for beta-galactosidase. In non-recombinant bacteria (those without the foreign DNA insert), beta-galactosidase is produced, which hydrolyzes X-gal, resulting in blue colonies.

6. **Resulting Colors**: In recombinant bacteria, since the LacZ gene is disrupted, beta-galactosidase is not produced, and thus X-gal is not hydrolyzed. This leads to the formation of white colonies. Conversely, non-recombinant bacteria, which can produce beta-galactosidase, will appear blue.

7. **Conclusion**: Therefore, the colonies of recombinant bacteria appear white because of the insertional inactivation of the beta-galactosidase enzyme due to the presence of foreign DNA in the LacZ gene.

**Final Answer**: The colonies of recombinant bacteria appear white in contrast to blue colonies of non-recombinant bacteria because of the insertional inactivation of the beta-galactosidase enzyme.

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