The Genetics of Twinning

So, I found out today that my great-Grandma and Grandpa Hanneman have 13 sets of twins in their family!  In fact, my great-grandma herself was a twin!  Apparently her sister died at birth, so that's why I never knew she was a twin.

It sounds like there are twins (and even some triplets) down other lines of my family, but we don't know just yet where in the family tree they fall.

I've always wondered what role genetics plays in the conception of twins, but only now do I have the motivation to look into it!  I did some reading on the Internet (I know you can't trust everything you read on the Internet, but several sites confirmed the same information), and here is what I came up with:

• Fraternal twins run in families on the mother's side only, if she inherits the gene for hyper ovulation (the tendency to release multiple eggs during ovulation).  Men can carry this gene and pass it on to their daughters; but since men don't ovulate, a family history of twins doesn't make them any more likely to have twins themselves.*
  
• Identical twins are random and do not run in families except by coincidence.*  The biological mechanisms that prompt the single fertilized egg to split in two remain a mystery.**

Obviously we won't know for a while if our twins are fraternal or identical, but we do know they are blessings from the Lord!  Praise God that He has blessed our family tree with many children! :-)

*http://multiples.about.com/od/pregnancy/a/familytwin.htm
**http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Twins_identical_and_fraternal?open