Question

What is subtractive hybridization?

Answer 1

To get the desired DNA segment so that subtractive hybridization could be done, restriction enzyme is very necessary. As this restriction enzyme helps in cutting the desired DNA sample. Then later hybridization takes place.

Complete answer:
Subtractive hybridization is a technique that is used for the isolation of a DNA segment that has been missing from a particular sample of DNA. Now to get the desired DNA segment we will require another DNA sample that has the desired sample.
For suppose a hereditary defect is because of the deletion of the DNA for a specific gene. A sample of DNA from the chromosome of the affected DNA individual will lack this specific segment of DNA. To get the missing DNA, we have to find a healthy individual and extract the DNA segment. Let us understand it through an example- the dmd gene i.e. a gene for duchenne muscular dystrophy, is present on the Xp21 band which is close to the middle of the short or p-arm of the X-chromosome. Using light microscopy, it was found that in a patient this Xp21 band was missing. So to rectify this, a healthy individual was identified from whom subtractive hybridization of the mutant chromosome with normal chromosome could be done so that the dmd gene could be cloned.

Note-
Sometimes a negative approach is adopted to find the cloned gene. Hybridization comes to the rescue as it is used for the removal of genes that are shared by two organisms, leaving behind the ones that are unique.