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Paternal Twins: Definition and Facts

At first sight, paternal twins look exactly alike. They’re the same sex, look exactly alike, and sometimes their parents dress them the same. Sometimes they seem to share the same gestures and personality. But how identical are they really?

newborn paternal twins

What are paternal twins?

Paternal twins are more commonly called identical twins. They can also be described as monozygotic twins. They form when a single egg is fertilized by a single sperm. This forms a zygote. After conception, the zygote splits in half, creating two individual embryos. Paternal twins have the same genetic origins and the same DNA because they come from a single fertilized egg. 

Medical experts are not sure what causes monozygotic twinning. One theory is that the egg divides in half as a malfunction of the normal development process. 

Unlike fraternal twins, paternal twins don’t run in the family, and there’s no hereditary trait that makes it more likely to have them. It seems to be purely a matter of chance and coincidence. Research tells us that monozygotic twins (paternal) occur about half as often as dizygotic twins (fraternal). 

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Fraternal vs paternal twins

The main difference between fraternal vs paternal twins is the number of fertilized eggs involved. Fraternal twins develop when two separate egg cells get fertilized by two separate sperm cells. On the other hand, paternal twins develop when one sperm fertilizes one egg. 

Paternal and fraternal twins are also known as monozygotic and dizygotic twins. Monozygotic twins form when a single egg gets fertilized by a single sperm making zygote. After conception, the zygote splits into two separate parts, creating two individual embryos. Dizygotic twins happen when two eggs get fertilized by two separate sperm. 

Another difference between paternal and fraternal twins is their genes. Monozygotic twins share the same genetic origins and the same DNA. On the other hand, dizygotic twins share about 50% of their genetic traits. 

Paternal twins' feet in mother's hands

Paternal twins’ characteristics

How paternal twins form

Paternal twins or monozygotic twins form when one sperm fertilizes one egg. The zygote then splits in two, creating two identical embryos. Although all paternal twins are formed very early in pregnancy, there’s 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 own amnion, chorion (both of which are membranes that cover an embryo), and placenta. 

Paternal twins’ appearance and behavior

Although they share the same gene set, paternal twins are two unique individuals. They come from the same fertilized egg, but each embryo is influenced by small differences in the environment in the womb. Once they’re born, external environmental factors are also at play. 

At first sight, paternal twins might seem completely identical. However, physical clues like moles, freckles, hairstyle, and body language can distinguish them. Although they share the same DNA, external factors can cause differences in their personality. 

How to know you’re expecting paternal twins

Mothers often wonder about the gender of their baby. It’s not uncommon for a pregnant mother to wonder if she’s carrying twins. Fortunately, modern technology makes it easy to determine if you’re pregnant with paternal twins. 

If you’re an expecting mother, you’ll probably have your first ultrasound sometime between 8–14 weeks of pregnancy. The person performing the ultrasound should be able to identify if you’re carrying multiple babies. The next step would be to identify whether the eggs are sharing the same placenta or have their own separate placentas. 

If you are expecting twins, it’s important to talk with your doctor about your health and nutrition. You may need different supplements than a person expecting a single baby, and you might need more frequent monitoring by your doctor.


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