Correlations were a little higher in monozygotic twins than dizygotic.
Monozygotic twins share 100% of their genes, whereas dizygotic twins share on average only 50%.
It is generally accepted that the most powerful of the designs is the twin study, using either genetically identical (monozygotic) twins, or fraternal (dizygotic) twins.
Dizygotic twinning is associated with maternal age and perhaps with social class.
The monozygotic twin sample comprised five male and five female pairs and the dizygotic twin sample three male and three female pairs.
In the absence of such findings it may be that one link between dizygotic twinning and reproductive potential may simply be high coital rates.
If the twins are dizygotic, there is only a 10% probability that the second twin will develop the disorder.
All the twin pairs thought to be dizygotic were proved to be so with a difference in one or more of the blood groups.
