12.4 Using Genomic Sequence to Find a Specific Gene 15 44200 GRIFFITHS FREEM Ch-12 First Pages Sen 12-10-2003 p 15 Application File on File chromosome maps in a variety of ways, by relating the locations of DNA markers to cytogenetic landmarks such as chromosome bands or to chromosome breaks of known position. Let’s look at some common techniques. IN SITU HYBRIDIZATION MAPPING If part of a ge-nome has been cloned, then it can be used to make a la-beled probe for hybridization to chromosomes in situ. The logic of this approach is identical with that of any hybridization technique, such as Southern blotting, ex-cept that here largely intact chromosomes are the target for probe hybridization (rather than DNA on a mem-brane). In this technique, cells are broken open and their chromosomes are spread out on microscrope slides. The DNA of the chromosomes is denatured so that their DNA is largely single stranded. Then the labeled probe, also denatured, is added to the preparation; the probe
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