Practice question

In random DNA with equal base frequencies, the probability of any specific n-base sequence occurring is 1 divided by 4 raised to power n. For tetranucleotide GATC, probability equals 1/256. To estimate frequency in a large genome, divide total size by 256. For a genome of one million base pairs, 1,000,000 divided by 256 yields approximately 3906 expected cleavage sites. This statistical model explains why four-base recognition enzymes generate numerous small fragments averaging 256 base pairs, useful for frequent cutting and fingerprinting, whereas six-base enzymes cut far less frequently.