DNATechnology160-page4

DNATechnology160-page4 - along with many transposons....

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Biotechnology - 4 Bacterial recombination can also take place by transduction, a process involving virus vectors, which can bring bits of DNA which were broken off from a previous host's DNA molecule when the virus left that host and add that DNA to a new bacterium. A virus can also be a cloning vector, and virus clone libraries are maintained. Natural Recombination in Eukaryotes Genetic recombination in eukaryotic organisms naturally occurs between homologous chromosomes with the following characteristics: Crossing over occurs anywhere along the chromosome Crossing over, except for mutations, is reciprocal and the crossing over distance is fairly extensive. Genetic recombination can also involve transposons, the jumping or mobile genes discovered in corn by Barbara McClintock in the 1940's, that are able to recognize specific DNA nucleotide sequences on both strands of DNA and make cuts into which they splice the DNA segments they are moving. In the 1970's, enzymes that could make these cuts were identified in bacteria,
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Unformatted text preview: along with many transposons. Because each enzyme recognizes a specific DNA sequence the enzymes were called restriction enzymes (or more properly restriction endonucleases) because they are restricted to one specific DNA code that they can cut. Restriction enzymes are used in recombinant DNA work. Restriction enzymes find sections of DNA where the order of nucleotides at one end is the reverse of the sequence at the opposite end. This way a restriction enzyme can cut tiny "sticky ends" of DNA and match that piece of DNA to "sticky ends" of any other DNA that has been cut with the same restriction enzyme. The cut DNA is then spliced into the second DNA molecule. This is what Barbara McClintock's jumping genes were doing. It's believed that the bacterial restriction enzymes are naturally used as part of the bacterium's defense system, to remove unwanted bacteriophage DNA from its genome....
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