a-Provide resistance against a substrate .
b-Inhibits the growth of normal cell in a culture .
c-Helps to create a chromosome map .
The correct option is: d- Both 1 and 2.
A selectable marker in genetic engineering serves two main functions:
- Provide resistance against a substrate: In the context of bacteria, the selectable marker is often a gene that confers resistance to a particular antibiotic or substrate. For example, genes that provide resistance to antibiotics like ampicillin, chloramphenicol, tetracycline, or kanamycin are commonly used as selectable markers. When the recombinant DNA is introduced into the host cells, only those cells that have successfully taken up the recombinant DNA (transformants) will express the selectable marker gene and thus become resistant to the antibiotic. Non-transformed cells, which have not incorporated the recombinant DNA (non-transformants), will remain sensitive to the antibiotic and will not survive in the presence of the substrate.
- Inhibit the growth of normal cells in a culture: Selectable markers allow for the identification and elimination of non-transformed cells in a culture. Since non-transformed cells are sensitive to the substrate (e.g., antibiotic), they will not be able to grow and form colonies in a culture medium containing that substrate. On the other hand, transformed cells (containing the selectable marker gene) will be resistant to the substrate and will survive and grow in the presence of the substrate. This selective growth of transformed cells makes it possible to isolate and identify cells that have successfully taken up the recombinant DNA.
Therefore, both functions of the selectable marker (providing resistance against a substrate and inhibiting the growth of normal cells in a culture) are essential for the success of genetic engineering experiments, as they enable the selection and isolation of cells or organisms that have incorporated the desired recombinant DNA.
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