Some Restriction Enzymes Cut at Specific and Unambiguous Sequences (E

Multiple Choice

Some restriction enzymes cut at specific and unambiguous sequences (e.g.,NotI at GCGGCCGC) .As such,the distance between two such sites in a large random DNA sequence is 4⁸.However,the sequence recognized by XhoII is said to be ambiguous (Pu-GATC-Py,where Pu = any purine and Py any pyrimidine) .What,therefore,is the expected distance between two XhoII sites in a large random sequence?

A) 4 × 4 × 4 × 4
B) 1 × 4 × 4 × 4 × 4 × 1
C) 2 × 4 × 4 × 4 × 4 × 2
D) 4⁶
E) 4² × 2²