A human gene, which we will call gene X, is located on chromosome 11 and is found as a normal allele and a recessive disease-causing allele. The location of gene X has been approximated on the map shown here that contains four STSs, labeled STS-1, STS-2, STS-3, and STS-4.

A. Explain the general strategy of positional cloning.
B. If you applied the approach of positional cloning to clone gene X, where would you begin? As you progressed in your cloning efforts, how would you know if you were walking toward or away from gene X?
C. How would you know you had reached gene X? (Keep in mind that gene X exists as a normal allele and a disease-causing allele.)

STS-1 STS-2 STS-3 Gene X STS-4