Question

What is the purpose of a selectable marker such as the antibiotic-resistance gene ampR?

l. Selectable markers allow a researcher to identify cells that have incorporated the recombinant plasmid.

ll. Selectable markers produce antibiotics, which kill cells that have not incorporated recombinant plasmid.

lll. Selectable markers prevent cells that have incorporated one plasmid from incorporating another.

lV. Selectable markers allow a researcher to identify the recombinant plasmid.

V. Selectable markers are only effective in viral vectors.

Answer 1

Answer- Part I is the correct answer.

Selectable markers allow a researcher to identify cells that have Incorporated the Recombinant plasmid. A selectable marker is a stretch of gene which is incorporated into a plasmid which helps in the maintainence of plasmid within a cell.

A selectable marker gene gives cell an ability to grow in selective conditions. It is mostly an antibiotic resistance gene or a herbicide resistance gene.

Example: ampR gene is a kind of selectable marker gene found on plasmids and those cells which have this plasmid is resistant against the antibiotic ampicillin. This means, it confers a bacteria the ability to grow even in the presence of the ampicillin in the medium. Normally, an ampicillin breaks the cell wall of a bacteria but in the presence of ampR selectable marker containing plasmid, catalysis of beta lactum ling of ampicillin would take place and the bacteria can grow.

Option II is incorrect because selectable markers do not produce antibiotics, rather they are genes which provide resistance against antibiotics.

Option III is incorrect because a selectable marker only helps the researcher detects that the cell has taken up the plasmid or not.There is no such proof that it prevent cells that have incorporated one plasmid from incorporating another.

Option IV is incorrect because selectable marker allows the researcher to identify the cell which would have incorporated the Recombinant plasmid and not the individual identification of a Recombinant plasmid.

Option V is incorrect because selectable markers are not only effective in viral vectors but are also effective in other vectors like bacterial plasmids.

So, option I defines the purpose of a selectable marker like antibiotic resistance gene like ampR.