Practice question

The expected occurrence of a restriction site in random sequence is calculated as genome size multiplied by 1/4^n where n is recognition length. For a six-base cutter, 4^6 equals 4096, so frequency is one site per 4096 base pairs. In the human haploid genome of approximately three billion base pairs, division yields 3x10^9 divided by 4096 equals approximately 7.3x10^5 sites. Considering GC content bias and approximations used in textbooks, this value is often reported in order of roughly one million sites, approximated as 1.2x10^6, demonstrating why six-base enzymes are considered rare cutters for genome mapping.