Suppose bacteria are grown on a petri dish that contains nutrient agar and the antibiotic ampicillin. After observing the bacteria growth on the plate for two days, you notice that only some of the bacteria have survived. What is a plausible explanation for your observations

The bacteria that survived were transformed with a plasmid that contains the resistance gene for ampicillin

Explanation:

1. Specially prepared bacteria are mixed with DNA (e.g., from a ligation).

2. The bacteria are given a heat shock, which causes some of them to take up a plasmid.

3. Plasmids used in cloning contain an antibiotic resistance gene. Thus, all of the bacteria are placed on an antibiotic plate to select for ones that took up a plasmid.

4. The plasmid contains an antibiotic resistance gene, a promoter to drive gene expression in bacteria, and the target gene inserted during the ligation.

5. Bacteria without a plasmid die. Each bacterium with a plasmid gives rise to a cluster of identical, plasmid-containing bacteria called a colony.