Expert: Bill Russo - 6/26/2006

Question
I am the oldest of 4 girls on my fathers side.  I have a pair of identical sibling girls on his side.  I also have a set of identical twin boys.  Everyone tells me it is from dad.  I say the egg determines quantity and father, the sex.  A female can inherit the trait can't she?  And what are the odds of any of my sons having multiples, or will that come from any female children they may have?  Thanks so much

Answer
Sometimes twinning is hereditary, it's true. However, only fraternal twins are influenced by heredity, and then only in some cases. If your mother or maternal grandmother was or had fraternal twins, you might have inherited a gene for hyper ovulation, increasing your chances of conceiving twins also. Identical twins are a mystery to science. There is no genetic link suggesting a predisposition to inherit a trait for the egg (zygote) to divide. The medical terms for the two types of twinning are monozygotic and dizygotic. When a woman’s ovaries produce multiple fertile eggs in one menstrual cycle, multiple fraternal births can occur. This trait, hyper ovulation, is caused by an overproduction of hormones and is defiantly hereditary. As far as the sex of the embryo, there is no evidence of the male or female contributing more to the outcome. There are plenty of “Old Wife’s Tales” that will predict anything you want them to, but the facts are the facts.