Paternal Twins versus Fraternal Twins: Characteristics and Surprising Facts

At first sight, the paternal twins may look exactly alike. They’re the same gender, look exactly alike, and even dress the same. But how identical are they? Let’s find out.

baby twins brother and sister one hundred days

What are paternal twins?

Paternal twins — more commonly called people identical twins — are monozygotic. Paternal twins form when an egg is fertilized by a single sperm, creating a zygote. After the conception, the zygote splits, creating two individual embryos. Because they come from a single fertilized egg, they share the same genetic origins and DNA.

However, their genetics may still differ from each other. Certain mechanisms happen thereafter the separation of the zygote, which can result in minor external differences in twins. After birth, environmental factors also influence the genetic expressions of twins, so even identical twins will still have individual personalities, behaviours, and physical traits.

It (monozygotic twins) occur in three to four per 1,000 births worldwide. According to various scientific research, most cases of monozygotic twinning don’t result from strictly genetic factors. However, some families may do have higher rates of monozygotic twins, so genetics may play a role. In any case, no single cause for monozygotic twinning has been identified.

What we do know that twin pregnancies are primarily a matter of chance. Monozygotic twins come from all around the world, but their presence varies by geographic location. For example, there are 1.3 cases of identical twins per thousand births in Japan but 50 cases per thousand births in Nigeria. On average, these twins happen in 13 of every thousand births.

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Fraternal vs paternal twins

The primary difference in fraternal vs paternal twins is the number of fertilized eggs involved. Fraternal twins develop when two separate sperm cells fertilize two eggs. In contrast, paternal twins (monozygotic twins) develop when one sperm fertilizes one egg; then, after conception, the zygote splits, creating two individual embryos.

These are (Paternal and fraternal twins) also known as monozygotic and dizygotic twins. Monozygotic twins share the same genetic origins, on the other hand, dizygotic twins share about 50 per cent of their genetic traits. They may differ in gender, and they always have their placenta and amniotic sac. Fraternal twins are as similar to each other as siblings in the same family.
The rate of fraternal twins is influenced by certain factors:

  • family history
  • use of some fertility treatments
  • use of assistive reproductive technology
  • age
  • BMI

Paternal twins’ characteristics

They are formed when one sperm fertilizes one egg. The zygote then splits, creating two identical embryos. Although they form early in pregnancy, there’s some variation in how early the fertilized egg divides

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How paternal twins form

Paternal twins (monozygotic twins) form when one sperm fertilizes one egg. The zygote then splits, creating two identical embryos. Although all paternal twins from early in pregnancy, there’s some variation in how early the fertilized egg divides.

In essence, if the egg splits earlier, the twins will be more independent and will have their membrane coverings (amnion and chorion) and placenta.

  1. If the separation occurs in the first one to four days after fertilization, then each of the monozygotic twins will have their placenta and amnion. And these twins can’t be distinguished from dizygotic twins before birth.
  2. Paternal twins (monozygotic twins) will have one placenta and two amnions if they separate on days four to eight.
  3. If the division took place from 8-12 days, then they will share a placenta and an amnion.
  4. Division after 12 days can lead to incomplete separation of embryos and the formation of сonjoined twins.

Paternal twins’ appearance and behaviour

Although paternal twins share the same genetics, they are two unique individuals. They form the same fertilized egg, but each embryo experiences small differences in their womb environment. Once they’re born, external environmental factors also play an important role.
At first sight, they may seem completely identical. However, physical clues like moles, freckles, hair growth, and body language may distinguish them. Although they share the same DNA, external environmental factors can cause differences in their personality and behaviour.

How to know you’re expecting paternal twins

Most parents may wonder about their baby’s gender. It’s not uncommon for pregnant women to wonder if they’re carrying twins. Fortunately, the modern age of technology makes it easy to determine if you’re pregnant with paternal twins.

If you’re expecting, you’ll probably have the first ultrasound sometime between 8 and 14 weeks. The ultrasound technician can identify whether you’re carrying multiple babies or not. Next, they can also identify whether the eggs share the same placenta and amnion or not. If the separation happened early and monozygotic twins have different placentas and amnion, you possibly won’t know you’re having identical twins until after their birth.

If you are expecting twins, your health care provider will offer proper guidance on nutrition. You may also need different prenatal supplements than a woman expecting a single baby, and you might need more frequent monitoring by a health care expert. Women with twin pregnancies have a higher chance of needing a cesarean section. By making some adjustments to your lifestyle and work routine, you’ll possibly give yourself and your twins a healthy head start.

Some surprising facts about fraternal twins?

1. Possibly they may have two different fathers.

That’s right — this isn’t just something that we’ve seen in movies. It’s a true phenomenon known as superfecundation or bi-paternal twins. It happens when a woman releases multiple eggs (known as hyper-ovulation), has sex with more than one partner, and then the eggs are fertilized by sperm from different partners.

2. They are the most common type of twins.

Most people tend to talk more about identical twins (because how wild, right?), but a twin pregnancy is much more likely to result in fraternal twins. All over around 75 per cent of all twins are fraternal.

3. They have separate supporting structures.

Fraternal twins occur when two different sperm fertilize two separate eggs, both of which then implant in the uterus? Because they are two separate eggs when they’re fertilized and implanted, they usually develop separate amniotic sacs, placentas, and other supporting structures.

4. They can be the same sex or different.

As is the case with any conception, chromosomes from the father’s sperm determine the gender. Since they originate from two separate sperm, each of those eggs could be a boy or girl. It means fraternal twins can both be boys, both be girls, or be a boy and girl. Of course, we are strictly speaking from a genetic standpoint — sex is determined in utero, while gender is a social construct and something a person decides for themselves later.

5. They may not be born on the same day.

They may not even be born in the same week or month! How is this possible? So, let’s say if a woman releases an egg during her cycle and it gets fertilized, but her cycle is interrupted. And by the time she experiences another cycle, thus releasing another egg, she is already pregnant. Then the second egg gets fertilized, too. It can take place up to 24 days after the first egg’s release, leading to twins born a few weeks apart (although they’re often born in the same general timeframe). And this situation is known as superfetation.

6. Can be hard to distinguish from identical twins.

For all of their differences, they could still look extremely similar — just as any siblings with shared genetic makeup can look extremely similar. Since environmental factors can lead to identical twins having slight physical differences, most people can’t distinguish fraternal twins from identical. The only 100 per cent accurate and easy way to tell the difference is through a DNA zygosity genetic test. It is done by swabbing each twin’s cheek.

7. They might be opposites.

Since they only share 50 per cent of their DNA, they can have very different characteristics and preferences. While you’ll undoubtedly love their individualism, it can make mastering their sleep routine a bit of a nightmare. This is why identical twins are usually closer than fraternal twins. When it comes to connection, identical twins have a stronger bond than fraternal twins because they share 100 per cent of their DNA.

8. Fraternal twins are the result of hyperovulation.

We established that they are formed when a woman releases more than one egg, and those eggs get fertilized by different sperm. But why a woman did release more than one egg in the first place? The culprit is hyper ovulation. Or the tendency to release multiple eggs during ovulation.

9. The highest number of fraternal twins come from Africa.

The rate of fraternal twins in Africa is around 14 fraternal twins per 1,000 births. Alternately, the lowest rate of occurrence — six per 1,000 births — is in Asia.

10. Fraternal twins may run in the family.

It’s long been believed by researchers that a woman who has a history of fraternal twins in their families are more likely to give birth to fraternal twins themselves. A woman who is born a fraternal twin has a one in 17 chance of conceiving fraternal twins, and a woman who has given birth to one set of fraternal twins is believed to be three times more likely to conceive another set.

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