In the technique of positional cloning, a researcher begins with a DNA library and selects a clone that is tightly linked to the gene of interest. That clone, or a piece of it, is then used as a probe to isolate an overlapping clone from a different DNA library. The second clone is used to isolate a third overlapping clone from the first library, and so on, until the researcher has “walked” along the chromosome to the desired locus. 

(a) How can the researcher walk consistently in the same direction along the chromosome during the cloning process? 

(b) What could happen if a long repetitive DNA sequence such as a transposon was situated between the starting clone and the gene of interest?