Expert: Dana Krempels, Ph.D. - 9/21/2007

Question
QUESTION: Does the possibility of having fraternal twins come from the mother or the fathers' genetic composition?

ANSWER: Dear Beth,

It is more likely that this tendency runs in the maternal line, since multiple ovulations are a process that occurs in the female, not the male.  Males will contribute thousands of sperm, no matter what.  So the limiting factor is the number of ova per ovulation.

Further genetic control of this phenomenon could be exerted at the level of a woman's likelihood to actually be able to *carry* two fetuses to term.  

So I'm thinking it's the mom, *if* the particular twinning does run in the family.  Sometimes it just happens by chance.

Hope that helps.

Dana

---------- FOLLOW-UP ----------

QUESTION: I wasn't talking about the release of the egg(s). I meant what part does the genetic background of the mother's parent's play.
For example I am currently pregnant with twins and on MY mother's side the only twins were my maternal Grandmother's sister's grandchildren. On MY father's side my paternal Grandmother had twin sibblings. So, my question is it more likely then not that my disposition to have twins came from my mother's side or form my fathers' side or is it the combination? I was wondering if it is like bullheadedness when the child gets that likelihood from the Mother's father.
Thank you,
Beth

Answer
Dear Beth,

It is likely, since twinning in both sides of your future children's families has been sporadic, at best, that this is not necessarily genetic, but rather due to chance.

In families that actually do have a genetic tendency towards twinning, the various factors that *promote* twinning are many, and they *do* include the tendency to ovulate multiple eggs during an ovulation cycle.  There isn't a gene labeled "twinning gene."  Twinning is the product of many different genetic and environmental influences.

As I mentioned before, since a genetic tendency towards twinning is expressed in the *female* parent (the father contributes sperm, and as far as we know, the genetics of the fetuses does not affect the mother's likelihood of twinning!), then it is YOUR genes--not your husbands--that are the basis of your genetic tendency (if you are, indeed, expressing that) for twinning.

If one of your twins is a daughter, however, and she shows a genetic predisposition for having twins, those genes for that predisposition may come from (1) you, (2) your husband, or (3) both parent.  It is HER genes that will likely be the major factor in her ability to produce twins, and those can come from either side of the family.

I hope makes it more clear.  Good luck with the twins!  :)

Dana