Which term describes the ampicillin resistance gene present in recombinant DNA that allows E. coli cells to become resistant to ampicillin?

Selectable marker

(c) selectable marker

In genetic engineering, a selectable marker is a gene that confers a specific trait, such as resistance to an antibiotic, which allows researchers to identify and select cells that have successfully incorporated recombinant DNA. In this scenario, the ampicillin resistance gene present in the recombinant DNA allows the host E. coli cells to become ampicillin-resistant when they take up the recombinant DNA. Therefore, the ampicillin resistance gene functions as a selectable marker in this process.

A selectable marker in genetic engineering serves as a means to identify and distinguish cells that have successfully taken up the foreign DNA (transformants) from those that haven't (non-transformants). It also allows researchers to selectively promote the growth of the transformed cells while inhibiting the growth of non-transformed cells.

During the process of transformation, a piece of foreign DNA is introduced into a host bacterium, such as E. coli. To identify which bacteria have successfully incorporated the foreign DNA, scientists need a way to distinguish them from the bacteria that have not taken up the DNA.

One common method is to use genes that confer resistance to antibiotics as selectable markers. E. coli cells, in their natural state, do not carry resistance against certain antibiotics like ampicillin, chloramphenicol, tetracycline, or kanamycin. Researchers engineer vectors, such as plasmids, to carry both the foreign DNA of interest and a gene that provides resistance to a specific antibiotic.

After introducing the engineered vector into the host bacteria, the bacteria are exposed to the antibiotic. The cells that have successfully taken up the vector and incorporated the foreign DNA will now possess the antibiotic resistance gene and can survive in the presence of the antibiotic. These cells are called transformants.

On the other hand, non-transformed cells that did not incorporate the vector will not have the antibiotic resistance gene and will not survive in the presence of the antibiotic. They will be eliminated, leaving behind the transformants.

In this way, selectable markers play a crucial role in genetic engineering experiments by enabling researchers to selectively grow and isolate the cells that have successfully undergone transformation and taken up the desired DNA fragment.