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.
Key Takeaways
- Identical twins originate from a single fertilized egg, while fraternal twins develop from two separate eggs.
- Identical twins share 100% of their genetic material, whereas fraternal twins share about 50%.
- Identical twins have the same physical characteristics, but fraternal twins can display significant differences in appearance.
Identical vs Fraternal Twins
Identical twins are babies that are born when fertilized eggs of a woman is divided into two parts, and so they share the same placenta and look alike when born. Fraternal twins are twins born when two separate eggs of a woman get federalized, and although they are born together, they look different.
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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
| Parameters of Comparison | Identical Twins | Fraternal Twins |
|---|---|---|
| Also called | Monozygotic Twins | Dizygotic Twins |
| Formed by | Forming several fetuses. | Separate fertilisation |
| Placentas | May be Same | Different |
| Chorionicity and Amnionicity | Can be Di-Di twins and other twins (Mono-Di, Mono-Mono, etc.) | Only Di-Di Twins |
| Hereditary | Not hereditary | Hereditary |
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
- 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.
- 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.
- 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.
- 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.
- 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.
- https://jamanetwork.com/journals/jamapsychiatry/article-abstract/491444
- https://psycnet.apa.org/record/1937-04406-000
- https://jamanetwork.com/journals/jamapsychiatry/article-abstract/490991
- https://link.springer.com/article/10.1007/BF01070219
- https://jamanetwork.com/journals/jamapsychiatry/article-abstract/493164
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Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.
