Do Twins Skip a Generation?

The Concept of Generational Twinning

Twins
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A commonly held myth about twins and multiples is that twins skip a generation. Some people think it's unlikely that a twin will have twins, but they may be more likely to have twin grandchildren. Is there any scientific basis for this belief?

Is Twinning Inherited?

The statement is based on the assumption that twinning is genetic and runs in families. However, if that was truly the case—if there was a twin gene—then twins would occur with predictable frequency in those families that carry the gene. Yet, there are very few incidences of families who have twins in every generation of their lineage. The gaps might be why some propose the "skip a generation" theory.

Some twinning can be attributed to genetics. While there is not technically a twin gene, there is a genetic component that makes some women predisposed to conceiving twins. Hyperovulation, the tendency for a woman to release more than one egg in a menstrual cycle, may be genetically influenced. If two or more eggs are fertilized, dizygotic (fraternal) twinning can occur. However, monozygotic (identical) twins are thought to be random; no genetic component has been identified that increases identical twinning.

Genetics of Hyperovulation

So far, the studies of specific genes have shown conflicting results as to whether they cause hyperovulation or increase the chance of having fraternal twins. Any discussion of a gene that causes hyperovulation is only theoretical. With that caveat, here is how the genetics would play out.

If the cause of twinning is related to hyperovulation, only the mother's genetics would influence the chances for her to have twins. The father’s role is irrelevant for the current generation. If relatives note that "twins run on your mother's side," a woman might be more likely to have twins, but not if "twins run on the father's side." This is only true for that generation, as the father's genetics will influence the chances of his offspring having twins.

If the gene was dominant, a woman would only need to have one parent pass the gene to her in order for her to hyperovulate. Things get more complicated if the gene is recessive and a woman would need to get copies of the gene from both parents in order to express it.

Twins Skipping a Generation

Children receive genes from both parents, and the mythical gene for hyperovulation might be passed on by either the mother or the father. While the mother expresses the gene by hyperovulating, the father would be a silent carrier of the gene.

The daughter of a couple where the father or mother is a carrier of hyperovulation genes may be more likely to have twins. The son of the couple would not, although he may be a carrier of the genes and his daughter may be more likely to have twins. If this gene existed and the couple didn't have a daughter, their sons wouldn't be more likely to have twins, but their granddaughters would, and the trait would have skipped a generation.

Example

Let’s look at a family example to understand this further. In this example, the gene is dominant and is expressed by females even if it is inherited from just one parent.

  • First Generation (Twins): Adam and Eve. Let’s assume that Eve has the gene for hyperovulation. They have six children. Two of them are fraternal boy twins, Jesse and James.
  • Second Generation (No Twins): Jesse and James grow up. They each produce three children, but no twins. Although they carry the gene for hyperovulation, they don’t ovulate. Therefore they don’t influence the possibility that their partners will conceive twins.
  • Third Generation (Twins): Jesse’s children; James’ children. These are the grandchildren of Adam and Eve. Jesse’s oldest daughter, let's call her Madonna,  gives birth to fraternal girl twins, Thelma and Louise. James’ youngest daughter, Beyonce, gives birth to fraternal boy/girl twins, Luke and Leia. Jesse and James may have passed the hyperovulation gene to their daughters.
  • Fourth Generation (?): What do you think will happen? The female offspring may have twins. Or they may not. The male offspring don’t contribute to the chances of their partner’s producing twins. But they may have twins or multiples for a variety of other reasons, and they can silently pass the hyperovulation gene on to future generations.

    From this example, you can see why it would appear that twins skip a generation. But it’s not a hard and fast rule. With many other factors contributing to twinning, the theoretical hyperovulation gene would simply be one factor that influences the process.

    A Word From Verywell

    Until a gene for twinning is identified, this discussion is simply a fun exercise in understanding genetics. As more and more couples use assisted reproduction drugs and technologies, the topic becomes more and more cloudy. You may be on dubious ground when discussing this for a family as fertility treatments may have played a role in hyperovulation and the birth of twins.

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