Medical Myth: Twins skip a generation

This month's medical myth debunked: Is it really true that twins skip a generation? Our expert, Dr Max Pemberton is here to debunk another myth. 

Where did the myth come from?

There is a lot of confusion around twins and the different types so there’s no surprise that there are myths around twins too. To understand why the idea that they can skip a generation is a myth, it’s important to understand about the two types of twins that exist.

Usually just one egg is released by the ovaries each month, but if two eggs are released and then fertilised, then non-identical twins occur. These twins therefore come from two separate eggs fertilised by two separate sperms so they are genetically the same as a brother or sister, it’s just that they develop in the womb together.

The other type of twin is identical twins. This is quite different and much rarer and occurs when a single fertilised egg splits in two as it’s growing. The resulting babies are from exactly the same fertilised egg and are therefore genetically identical. 

 

What about non-identical twins?

Usually, one egg develops and is released from the ovaries each month. However, a certain gene that has been identified that, when present, can increase the chances that a woman will release more than one egg at a time when she ovulates.

As explained earlier, if these are then fertilised, then non-identical twins occur. This gene doesn’t ‘skip’ generations though. However, as boys don’t ovulate, it’s possible that if one generation has all boys, then the effects of this gene wouldn’t be seen until these males then have their own daughters which they pass the gene on to and they may then have twins.

This would give the illusion that the twins have ‘skipped’ a generation.

 

What about identical twins?

No gene has been found that’s responsible for causing identical twins, so it’s not passed down in families and certainly doesn’t skip generations. If there are more than one set of identical twins in a family, this is just coincidence.