AP BIOLOGY

Detailed explanation-1: -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. Bacteria without a plasmid die. Each bacterium with a plasmid gives rise to a cluster of identical, plasmid-containing bacteria called a colony.

Detailed explanation-2: -Only some bacterial cells absorb new DNA. Since the plasmid includes both the DNA of interest and a gene that confers resistance to a specific antibiotic, applying the antibiotic to the bacterial cells (i.e., antibiotic selection) can help determine which cells were genetically modified.

Detailed explanation-3: -Historically, antibiotics have also been used to disrupt genes at the chromosomal level. Scientists introduce an antibiotic resistance cassette within the coding region of the gene they are trying to disrupt or delete, which both inactivates the gene and acts as a marker for the mutation.

Detailed explanation-4: -Plasmids can transfer between different bacteria This means that a bacterium can become resistant to multiple antibiotics at once by picking up a single plasmid. They then become multidrug-resistant. Furthermore, genes that influence bacterial virulence are also frequently found on plasmids.

Detailed explanation-5: -Antibiotics commonly used for plasmid selection These antibiotic resistance genes not only give the scientist with an easy way to detect plasmid-containing bacteria, but also provide those bacteria with a pressure to maintain and replicate your plasmid over multiple generations.