Question

The possible number of SalI restriction sites in a 9 kb double-stranded DNA with equal base proportion (nearest integer) is \(\underline{\hspace{1cm}}\).

Hint:

For restriction sites: Expected sites = sequence length / \(4^n\), where \(n\) is recognition length.

Answer 1

Correct Answer: 2

SalI recognizes a 6 bp sequence (GTCGAC).
Probability of any specific 6 bp sequence when bases are equally distributed:
\[ P = \left(\frac{1}{4}\right)^6 = \frac{1}{4096} \]
Expected number of sites:
\[ N = \frac{9000}{4096} = 2.20 \]
Rounded to nearest integer:
\[ N = 2 \]