Final answer:
To isolate the gene encoding a scorpion toxin, a cDNA library should be created because it includes only those genes that are actively expressed, making the isolation process more efficient.
Step-by-step explanation:
The molecular biologist looking to isolate a gene from a scorpion that encodes a deadly toxin for the purpose of producing it in bacteria should create a cDNA library. This is because a cDNA library contains sequences from only those genes that are actively being expressed and translated into proteins. In contrast, a genomic library includes all genomic DNA sequences – coding, non-coding, introns, and control regions. Since the biologist is interested in the toxin, a protein product, the relevant gene would be actively expressed and therefore, present in the mRNA pool of the scorpion cells producing the toxin. Moreover, creating a cDNA library will streamline the process since it will not include non-coding and regulatory sequences, making the isolation of the toxin gene more efficient.
To create a genomic library, genomic DNA fragments would be cloned into vectors and would contain the entire genetic material of the organism. While this could be used for isolating genes, it may be less efficient for the biologist’s purpose. The creation of a cDNA library involves reverse transcribing mRNA from the tissue expressing the toxin into cDNA, which can then be cloned into vectors. This is advantageous for isolating a gene encoding a protein that is of commercial interest - such as an organic insecticide produced by bacteria.