Tuesday, June 7, 2011

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).


  1. Interesting, but I think you vastly under-estimated the number. I'm no biologist, but see the following discussion of meiosis and chromosomal crossover:
    So, for each of the 23 chromosomes you provided, it's not simply a question of did you provide copy A or copy B but which of the probably infininite combinations of A and B did you provide? An accurate calculation would replace the 2 (base of the exponent) with something much, much larger! So, 70 trillion is a gross underestimate, even without random mutation.

    Anyway you slice it, however, Aida is more unique and special than we can ever comprehend...

  2. Yeah, I think you're right. The 1 in 70 trillion would be the absolute minimum, but any of the combination of chromosomes would bump that number up way beyond what I was considering. Thanks.