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d 1s m1ss1ng c 1s m1ss1ng d 1s m1ss1ng c 1s m1ss1ng i

FIGURE 22.09 Restriction Fragment Length Polymorphism (RFLP)

DNA from related organisms shows small differences in sequence that result in changes in restriction map patterns. In the example shown, cutting a segment of DNA from the first organism yields six fragments of different sizes (labeled a-f on the gel). If the equivalent region of DNA from a related organism is digested with the same enzyme we would expect a similar pattern. Here, a single nucleotide difference is present, which eliminates one of the restriction sites. Consequently, digesting this DNA only produces five fragments, since site iii has been mutated and the original fragments c and d are no longer separated. Instead a new fragment, the size of c plus d is seen.

FIGURE 22.10 Antibiotic Resistant Cloning Plasmid

Genes for colicin production

Remove colicin genes and add ampicillin resistance gene

Ampicillin resistance gene

Remove colicin genes and add ampicillin resistance gene

FIGURE 22.10 Antibiotic Resistant Cloning Plasmid

The ColE1 plasmids of E. coli have been modified for use as cloning vectors. The original colicin genes have been deleted so that the bacteria carrying these plasmids no longer produce these antibacterial toxins. In addition, a gene for antibiotic resistance has been added. This provides an easily identifiable phenotype to the bacteria that carry the altered plasmid.

Multicopy plasmids are convenient as vectors since they make plenty of plasmid DNA and also express cloned genes at high levels.

Vectors are often designed to be selected by antibiotic resistance.

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