That's a good question. There are a number of ways of producing a new genome.
It would depend on how you define mutation. Would you include a copying error or only something caused by something like a cosmic ray? Do you include recombinations of the existing chromosomes of parents?
How would you count changes? Everyone has a few changes from their parents. Do all changes count equally? What about changes that have large effects on the phenotype?
What do you mean by 'based off'?