Difference Between Identical and Fraternal Twins (With Table)

Most of the women get pregnant with one baby, while some get pregnant with two, three, four, or even more than that at a time. This mostly depends upon that genetic factors, but it is also possible a couple gets pregnant with more than one baby for the first time in the family history.

Conceiving two babies are terms as twins. This is not very rare but not as common as well. Mostly twins look similar with several same features, and for a stranger, it is difficult to distinguish between them. There are two types of twins, identical twins and fraternal twins. Both of them are similar but more different at the same time.

Identical vs Fraternal Twins

The difference between identical and fraternal twins is that both of them have different scientific names. Monozygotic twins are identical twins, while dizygotic twins are fraternal twins. They are formed by different processes. In the case of identical twins, it is formed when the fertilized eggs split into two eggs, and therefore twins are born, while in fraternal twins, more than one egg is fertilized by the sperm, in case of identical twins, both share the same placentas while in fraternal twins both of them have different placentas, fraternal twins can be only Di-Di Twins while identical twins can be Di-DI twins, Mono-Di, Mono-Mono, and conjoined twins as well, except them there is much other difference among them, those are mentioned below.

In identical twins, the fertilized eggs of the women get divided into two parts within few days of conception, and the reason behind calling them monozygotic is that they are formed from the same zygotes. The fertilized eggs split then developed into two babies, and as they originally belonged to the same eggs, both of them may share the same placenta. It is a less common type of twin.

Fraternal Twins are types of twins born with different eggs. It happens wham two eggs of the women get fertilized by the sperm. They are called dizygotic as they are formed with two different zygotes. Usually, one egg is fertilized, but in this case, two eggs of the woman fertilize, which results in two babies, and as babies are born with different eggs, they also have different placentas. These types of twins are common.

Comparison Table Between Identical and Fraternal Twins

Parameters of ComparisonIdentical TwinsFraternal Twins
Also calledMonozygotic TwinsDizygotic Twins
Formed byForming several fetuses.Separate fertilisation
PlacentasMay be SameDifferent
Chorionicity and AmnionicityCan be Di-Di twins and other twins (Mono-Di, Mono-Mono, etc.)Only Di-Di Twins
HereditaryNot hereditaryHereditary

What are Identical Twins?

Identical twins look exactly like a mirror image of each other. They are also called maternal twins. Around 1 in 333 pregnancies, there is a chance of identical twins as they are not formed due to any hereditary factor and hence not passed down in genes. Fewer women can have identical twins when then fertilized eggs get split. There is a high chance that both babies share the same placenta. They can be Di-Di Twins where embryos are split after 3 to 2 days of fertilization, Di-Mono Twins where embryos are split after 3 to 8 days of fertilization, Mono-Mono Twins where embryos are divided after 8 to 13 days of fertilization, and lastly Conjoined Twin where embryos division take place after 13 days of fertilization. There is a high chance that babies, in this case, have joined body parts.

Both babies share identical chromosomes as they are formed from the same egg and sperm. Also, there is a high chance they have the same eye color and other physical characteristics as well. They may have the slightest difference due to the environmental factors they are birthing in.

What are Fraternal Twins?

These twins are not genetically identical but have only 50 percent of the genetic identity, and therefore, they are also known as non-identical twins. Most twins belong to this type of twins as they are born due to hereditary factors. Twins born as fraternal can be of different sex. Therefore they can be Boy and boy, girl and girl, and girl and boy. 

The most interesting fact about fraternal twins is that babies can also belong to two different people or, in simple terms, have two different gathers. This happens when the eggs get fertilized by different sperms. It is rare but a fact. There is also a chance that both of the babies might not be born on the same day. 

They are the result of hyper ovulation. It was a condition when women released more than one egg. They are common in Africa and rare in Asia. The embryos in this twin also split after 2-3 days of fertilization. It is easy to distinguish between babies in this as they can be of different sex and characteristics.

Main Differences Between Identical and Fraternal Twins

  1. In terms of genetic identity, both of them are different as identical twins as born from the same egg carry identical genomes whereas fraternal twins born from different eggs but same female have only 50% identical genomes.
  2. In terms of appearance identical twins are alike; it is comparatively more difficult to distinguish between both of them whereas fraternal twins are like siblings that can be differentiated relatively easier.
  3. They also differ when it comes to sexes, where again the fertilized eggs play the vital role, as identical twins share the same part of eggs, therefore, both of them have same-sex along with the same blood group while different eggs may also lead to different or same-sex and different blood groups in case of fraternal twins.
  4. Identical twins are less common as they are not due to hereditary factors it can happen to any woman and therefore only one-third of the twins are identical whereas fraternal twins are always hereditary which is common and hence two-third of the twins are fraternal.
  5. Some Twins are more like to suffer from TTTS that is a twin-to-twin syndrome that can be life-threatening to one or both babies, this syndrome is more like to develop in identical twins whereas there is a low risk of TTTS in Fraternal Twins.

Conclusion

Therefore with all the above differences, it will be easier to distinguish between types of twins, whether they are identical or fraternal. Both of them are different due to different formation patterns. Despite their differences, they have certain similarities, such as; both of them are produced during the same pregnancy, both of the babies or twins share many similar features and personality characteristics, eye color of both types, and twins are different from each other.

The maximum number of babies that can be born at a time is 8. Differentiating between twins or babies for a stranger can be quite a difficulty, but for their parents, it is as easy as to differentiate between two different normal babies.

References

  1. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/491444
  2. https://psycnet.apa.org/record/1937-04406-000
  3. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/490991
  4. https://link.springer.com/article/10.1007/BF01070219
  5. https://jamanetwork.com/journals/jamapsychiatry/article-abstract/493164
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