What steps make PCR a chain reaction that can produce millions of copies of a specific DNA molecule in a matter of hours without using host cells?

Write a short essay or sketch a diagram that provides an overview of how recombinant DNA techniques help geneticists study genes.
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Key Concepts
Recombinant DNA Technology
Gene Cloning and Expression
Applications in Genetic Analysis
How has DNA-sequencing technology evolved in response to the emerging needs of genome scientists?
How can gene knockouts, transgenic animals, and gene editing techniques be used to explore gene function?
What roles do restriction enzymes, vectors, and host cells play in recombinant DNA studies? What role does DNA ligase perform in a DNA cloning experiment? How does the action of DNA ligase differ from the function of restriction enzymes?
The human insulin gene contains a number of sequences that are removed in the processing of the mRNA transcript. In spite of the fact that bacterial cells cannot excise these sequences from mRNA transcripts, explain how a gene like this can be cloned into a bacterial cell and produce insulin.
Although many cloning applications involve introducing recombinant DNA into bacterial host cells, many other cell types are also used as hosts for recombinant DNA. Why?
