Question

A eukaryotic gene has "sticky ends" produced by the restriction endonuclease EcoRI. The gene is added to a mixture containing EcoRI and a bacterial plasmid that carries two genes conferring resistance to ampicillin and tetracycline. The plasmid has one recognition site for EcoRI located in the tetracycline resistance gene. This mixture is incubated for several hours, exposed to DNA ligase, and then added to bacteria growing in nutrient broth. The bacteria are allowed to grow overnight and are streaked on a plate using a technique that produces isolated colonies that are clones of the original. Samples of these colonies are then grown in four different media: nutrient broth plus ampicillin, nutrient broth plus tetracycline, nutrient broth plus ampicillin and tetracycline, and nutrient broth without antibiotics.Bacteria that contain the plasmid, but not the eukaryotic gene, would grow __________.A) in the nutrient broth plus ampicillin, but not in the broth containing tetracycline. B) only in the broth containing both antibiotics. C) in the broth containing tetracycline, but not in the broth containing ampicillin. D) in all four types of broth. E) in the nutrient broth without antibiotics only.

Answer 1

D. In all four types of broth.

Explanation:

The plasmid will provide the origin of replication to the gene in question as it is a self-replicating body in the bacterial cell. The recombinant DNA technology is used for the purpose but here the plasmid itself has resistant gene for ampicillin and tetracycline.

The plasmid minus the eukaryotic gene can survive on all the media with or without antibiotics as it is resistant to both. In normal media, it will also survive and grow. So, colonies are seen after incubation in all the four media.

The plasmid is ampicillin resistant so grow in all the media.

The plasmid is also tetracycline-resistant so would grow in media having broth of tetracycline or both ampicillin and tetracycline.