Specific genes or sequences that are single-copy are much more difficult to isolate because they represent such a small percentage of the total DNA of an organism. Southern blot a method of visualizing particular DNA fragments involving electrophoretic separation and transfer of the fragments to a solid support such as a nylon membrane. The membrane can then be exposed to a labeled probe that will bind to the specific fragments of interest and allow their visualization independent of what may be many thousands of other fragments from the gel. When the DNA of interest represents only a fraction of the originally cloned insert , subcloning is often done to facilitate handling of the clones as smaller clones are often less cumbersome to work with. Higher temperature and lower salt conditions result in higher specificity of probes or primers .
Repeat units can be short nucleotide sequences or entire sets of genes .
Many different vectors have been identified and genetically engineered for use in molecular biology. DNA inserted into a vector will be replicated along with the vector. In this manner, DNA of interest can be obtained in large quantities i.e., cloned. See tandem array and core sequence . Use your browser's BACK button to return to text.