Final answer:
To calculate the average frequency of a recognition site in a genome, you determine the probability of each nucleotide occurring, raise this to the power of the length of the site, and then divide the total number of nucleotides by this value.
Step-by-step explanation:
The average frequency of occurrence of a recognition site can be calculated by using probabilities based on the nucleotide composition of the organism's genome. For example, if the recognition site is a 4 nucleotide sequence and each nucleotide has an equal chance of occurring (25% for each of the four nucleotides: adenine, thymine, cytosine, guanine), the probability of the specific sequence occurring is (1/4) ^ (number of nucleotides in the sequence).
In a case where the sequence is 4 nucleotides long, the calculation would be (1/4)^4, which is 1/256, meaning that on average, this particular recognition site would be expected to occur once every 256 nucleotides. To apply this to an entire genome, you would divide the total number of nucleotides in the genome by the expected frequency. This gives you the average frequency of occurrence for that recognition site within the entire genome.
In practice, recognition sites may have different probabilities if the genome has a non-uniform distribution of nucleotides, but the overall approach to calculating average frequency remains the same.