One flaw about the child

So, as I get it, to complete the "small" loop, 20 years old Jane must give birth to a baby identical to herself as a baby. This is explained by her partner having the same DNA, so the baby gets the same. Though this can't be true in reality. A lot of factors affect the development of embryo and the DNA in the first cell will always be slightly different even if you clone someone and if you keep going at some point the result will be too different. This coincidence is pretty much astronomically impossible. So, I guess we should just assume that it occurred. I still don't know too much about this stuff, so feel free to correct me. I think this was a brilliant movie, anyway.