What's the difference between identical and fraternal twins?

Interested in finding out what the difference between identical and fraternal twins is and a bit more about twins in general? Well, you're in luck because the difference is pretty easy to explain. Even though there will be a bit of medical language, we'll keep it all nice and simple.


The difference between identical and fraternal twins is created when fertilisation occurs. Fraternal twins are created from 2 separate fertilised eggs so they normally develop separate separate amniotic sacs, placentas, and supporting structures. With identical twins, the siblings are created from one egg that divides into two. They may or may not share the same amniotic sac because that depends on when the single egg splits.


If the siblings are not the same sex, obviously they're fraternal twins rather than identical ones. This means they do not have the same DNA. The boy will have XY chromosomes and the girl will have XX chromosomes. You get boy and girl twins when one X egg is fertilised by an x sperm and a Y egg is fertilised by a Y sperm.

Look alikes

Identical twins have the same DNA but that doesn't mean they will look alike. Environmental factors such as womb position and the siblings' life experiences after birth can change their appearances so often you can't tell if the siblings are twins or not.

Identifying in the womb

It's possible for heathcare professionals to identify whether twins are fraternal or identical while they're still in their mother's womb. With modern ultrasound technology it's possible but only DNA testing can confirm either way.


Although the difference between identical and fraternal twins is created at birth, as the twins grow they also change. Whether twins are telepathic and if they can feel each other's pain, we'll leave to sci-fi writers and chat room users because there's no scientific proof of any of the more far-fetched theories about twins.

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