Genetics and Identical Twins – Is There a Connection?

Whoa, surprise! Sometimes couples get quite the shock when instead of one developing child appearing on the ultrasound monitor, two are wiggling about! 

And when they finally arrive looking like exact copies of one another, that’s a case of identical twins. And at some point, this leads to questions. 

Do genetics play a role in having identical twins?

Well, scientists don’t think so but they aren’t completely firm one way or the other. While most studies point toward “no,” there are some families who have produced a higher-than-normal number of identical twins. And that has led to some wiggle room for uncertainty among researchers. But overall, they believe genetics and identical twins don’t share much of a sandbox. 

Identical twins and genetics may not necessarily have a strong link, but that doesn’t mean that fraternal twins fall into that same category. Sometimes people are bit confused by the difference and why they are different. Are you one of them? (Pssst… it’s OK.)

Don’t worry, we’ve got you covered! Read on to find the answers to the “how” and “why” questions that may be currently bubbling up in your mind. After you’re through with this brief article, you can sound like an expert to others!

What Causes Identical Twins?

How did Mom and Dad get two copies of what appears to be the same child? Does it run in the family? How are they different from fraternal twins? Let’s dive right in. 

Do Identical Twins Run in Families?

As noted before, some families have produced a higher-than-normal number of identical twins. So, do identical twins run in families? Researchers say…nope. 

Is There an “Identical Twin Gene”?

The “identical twin gene” is a concept some people may believe in, but scientists largely disagree. While it is possible that genes involved in sticking cells together (called “cell adhesion”) may contribute to identical twins being produced, there’s no “identical twin gene.”

Of course, not all twins are identical. There are also fraternal twins, as we mentioned above. Their origin is a bit different.

Do Fraternal Twins Run in Families?

Instead of one egg being fertilized by one sperm, two egg cells are each fertilized by a different sperm. This results in two babies who develop side-by-side concurrently, but they’re no more similar than any other siblings.

This is because each is made of up a different sperm and different egg, so their genetic recipes are different from one another. 

And here’s where things continue to differ between fraternal and identical twins. Fraternal twins can run in families (source).

According to a report in The American Journal of Human Genetics, researchers conducted a study involving data from 2,000 mothers of fraternal twins. They looked at DNA bases called single nucleotide polymorphisms.

(Wow, that’s a big term. You might even be stuck for a moment, trying to think how you might pronounce that term. We can call them “SNPs” from now on. Much easier.)  

These SNPs can vary from person to person. Scientists looked at which ones appeared more frequently in mothers of fraternal twins. After going through piles upon piles of data, they narrowed things down to just two specific SNPs. 

What they found was women who have a copy of each SNP have a 29% higher chance of having fraternal twins.

No such occurrences have been found for identical twins. 

How are Identical Twins Conceived? 

When it comes to identical twins, it starts off the traditional way: one egg being fertilized by one sperm. This creates what’s called a zygote. But then that zygote splits into two, each its own embryo with the exact same genetic makeup. And those two embryos begin to develop in the womb, each a separate baby. 

Chances of Having Identical Twins

Statistically speaking, everyone has the same chance of producing them: about 1 in 250 (source). Whether you have twins in your family or not, those odds don’t change.

So identical twins: scientists don’t think it looks like genetics play a clear role. But it’s a different story for fraternal twins. Glad we have that settled. 

But that leads to another question…

Who Carries the Genes for Fraternal Twins?

Fraternal twins come from the mother’s side. That answer seems simple enough, but let’s dig a little deeper. What specific factors influence that likelihood of fraternal twins in the first place? 

Factors That Influence the Probability of Fraternal Twins

Perhaps you’re looking through your own family history and wondering if it fraternal twins could become a reality for your family. Let’s break it down…

Hyperovulation on Mother’s Side of Family

The women who produce fraternal twins release two eggs during their respective cycles. Releasing these multiple eggs is called hyperovulation, and it is an inherited trait. Women with a mother or sister who have had fraternal twins are about twice as likely to have fraternal twins themselves.

Age

How many birthdays you’ve had is also a factor. Those over the age of 35 have a higher chance of having twins because as they age, women tend to release more than one egg while ovulating.

Ethnicity

Where you’re from plays a role (source). According to data, fraternal twins are the most common among African people. In Nigeria, twins occur one in every 20-30 pregnancies. This, however, comes with a caveat: 

Nigerians who live outside their home country have a lower likelihood of having fraternal twins, so perhaps diet and environmental factors play a role there. 

Twins happen in one of every 60 pregnancies in Western Europe. And the rarest ethnicity to experience this phenomenon? 

Japanese.

Related Questions:

Can a twin have twins? 

Yes, but the above information is what impacts those chances. 

What are the chances of having triplets? 

This only occurs in about one in 10,000 pregnancies (source).

While discussing multiple births, it’s also important to bring up another topic:

How Do Fertility Treatments Impact Having Twins? 

The chance of having a “multiple” pregnancy (more than one baby developing in the same womb at one time) also balloons through the use of fertility medications to undergo ovulation induction or superovulation. (Superovulation is what happens when a woman uses certain drugs to stimulate the ovary to produce up to three eggs within a single cycle.)  

A drug called clomiphene citrate statistically leads 5% to 12% of women taking it to produce twins and less than 1% to have triplets … or more (…quadruplets, quintuplets, sextuplets, etc.)

That’s a lot of diapers to change. 

Parting Thoughts 

Mary Kate and Ashley Olsen; Dylan and Cole Sprouse; Jonathan and Drew Scott; Arnold Schwarzenegger and Danny DeVito … twins are a part of our world. And you never know when another set will make their grand debut on those ultrasound monitors.

Hopefully, now you have a better understanding of the story behind twins and the differences between identical and fraternal.

Maybe you think you could have twins one day. Or maybe someone you know wonders about their chances. Either way, now you can speak about it with a deeper understanding. For others who are curious, don’t hesitate to share this article!