Number Crunching

OK, so this story of twins marrying twins and having twins is fun but

Soon afterwards, despite a million-to-one odds, Diane and Craig went on to have identical twins of their own – Colby and Brady, now seven.

Odds of monozygotic twins are some three in a thousand. So the odds of this couple having such is indeed three in a thousand. The one in a million might be reached by counting the odds of the parents being twins, but as that had already happened that doesn\’t influence the odds of their having twins themselves.

When actually checking these numbers I was a little surprised to see that monozygotic twins are not thought to be influenced by genes (unlike non-identical such) but that i in a million is wrong all the same.

4 thoughts on “Number Crunching”

  1. Also, in a world of 6 Billion people, one in a million is going to happen to quite a few of them anyway.

  2. Just the other day, a commentor over at gnxp.com left an interesting link involving
    twinning, chimeras, etc. According to what I’d read in the link, there is a far greater than normal likelihood of homosexuality among male identical twins and that is related to genetic tendency toward increased fertility among their female relatives. It stated that many among the general population were originally (identical) twins in which one didn’t survive–but in many cases had been at least partly absorbed by by he survivor (resulting in an individual some parts of whom are chimerical). Confusing–but maybe worth reading.

  3. And even if you start from the parents and talk about the odds of an identical twin having identical twins, the odds are still only 1/333 x 2/333 = 1:55,555.

    So this is a “journalist’s million”.

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