Chapter 9, Problem 23P

a.	To make a genomic library useful for sequencing an entire genome, why would you ordinarily fragment the genomic DNA by mechanical shearing forces like sonication rather than by cutting the DNA with a restriction enzyme?
b.	Suppose that you wanted to make a genomic library to determine the complete sequence of a newly discovered organism’s genome, but you did not have a sonicator readily available. Explain how you could nonetheless use two or more restriction enzymes to make libraries whose clones could be sequenced so that a computer could assemble the genomic sequence.
c.	Suppose you only had a single restriction enzyme available, and you want to make a single genomic library from which you could assemble the genomic sequence. How might you be able to achieve this goal? (Hint: See Problem 9.) To make this library, would it be preferable to use a restriction enzyme that recognizes a 4-base, 6-base, or 8-base sequence of DNA?