I was talking to Liz about Aida (our new child) the other day. She wanted to see a catalogue of what all the different versions of our children would look like. "Hmm...", I thought. "I think that would be quite a big catalogue." It's currently impossible to produce such a catalogue as we don't know all the genes that contribute to appearances. However, I did figure out how unique Aida is.
There are 46 chromosomes per individual. During reproduction 23 chromosomes come from each parent. Therefore, there are 223 (8,388,608) different possible reproductive cells per parent. Each egg could combine with any of the 223 different sperms, so there are 8,388,6082 or 70,368,744,177,664 (70 trillion) different combinations of people that could result between any human couple.
Aida is not so much one in a million, but 1 in 70 trillion. (This does not take into account random mutation.)
If we were going to look through the catalogue, at one snapshot a second, it would take a million years to see every possible combination.
If Liz and I were any other of the great apes, Aida would be far more unique, 1 in 281,474,976,710,656 (281 trillion) as most of the great apes have 48 chromosomes rather than 46 (one of ours got fused along the way).