Question

In genetic engineering antibiotic resistance genes are used

• A. for keeping cultures free of infection
• B. as selectable markers
• C. as sequences where replication starts
• D. to select healthy vectors

Answer 1

The correct option is B as selectable markers

Genetic engineering
The modification of the genetic material (RNA or DNA) of organisms to use them to produce commercially important substances is called genetic engineering.

Antibiotic resistance gene
Antibiotic resistance gene is a type of selectable marker to separate the transformed cells from the non-transformants after cloning. Alien gene is inserted at this site. The cells are then placed on the growth medium with the respective antibiotics that retards their growth, hence they can be separated from the non-transformants.

Infection free cultures
Cultures are kept free of infection by using sterile media and working in a sterile environment.

Vectors
Vectors are the DNA molecules which can carry the foreign DNA fragment into the host cells for cloning. Examples include plasmids and bacteriophages. Antibiotic resistance genes are present on vectors to select transformed cells. It cannot select healthy vectors.

Origin of replication
The ori site or origin of the replication site is a specific nucleotide sequence on the vector DNA that initiates replication, without being dependent on genomic DNA for replication. Any piece of DNA when linked to this sequence can be made to replicate within the host cells.

Final answer:
c. as selectable markers