What do white colonies indicate in blue-white screening?

What do white colonies indicate in blue-white screening?

• A. They represent a lack of recombinant plasmids
• B. They indicate contamination in culture
• C. They have recombinant plasmids and cannot hydrolyze X-gal
• D. They produce blue pigment in media

Answer: (C)

White colonies in blue-white screening indicate that these colonies contain recombinant plasmids that cannot hydrolyze X-gal. Blue-white screening is a technique used to determine the presence of recombinant DNA in bacterial colonies. In this method, a plasmid containing a gene for lactase (the enzyme that breaks down X-gal) is used. When the plasmid is taken up by competent bacterial cells and is not recombined with the DNA insert, the bacteria can produce lactase, which hydrolyzes X-gal, leading to blue colonies. Conversely, when the plasmid includes an insert of foreign DNA, it interrupts the gene for lactase. As a result, the bacteria containing these recombinant plasmids cannot produce the lactase enzyme to hydrolyze X-gal, leading to the formation of white colonies. This clear distinction between blue and white colonies allows researchers to identify colonies that potentially contain the desired recombinant plasmid with the gene of interest.

White colonies in blue-white screening indicate that these colonies contain recombinant plasmids that cannot hydrolyze X-gal. Blue-white screening is a technique used to determine the presence of recombinant DNA in bacterial colonies. In this method, a plasmid containing a gene for lactase (the enzyme that breaks down X-gal) is used. When the plasmid is taken up by competent bacterial cells and is not recombined with the DNA insert, the bacteria can produce lactase, which hydrolyzes X-gal, leading to blue colonies.

Conversely, when the plasmid includes an insert of foreign DNA, it interrupts the gene for lactase. As a result, the bacteria containing these recombinant plasmids cannot produce the lactase enzyme to hydrolyze X-gal, leading to the formation of white colonies. This clear distinction between blue and white colonies allows researchers to identify colonies that potentially contain the desired recombinant plasmid with the gene of interest.