Identical twins have hundreds of differences across the entire genome. None of those are carefully planned. Prior to that, during generation of sperm and egg,

Identical twins have hundreds of differences across the entire genome. None of those are carefully planned. Prior to that, during generation of sperm and egg, many other unintended mutations occur. Each chromosome typically breaks and misjoins (crossing haphazardly with the matched one) about 3 times. This experiment is really mild by comparison.