1 in 70 trillion

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).