Conjoined twins

And after Identical of fraternal twins post, let's go deeper to one of the most intriguing malformations in human beings: the conjoined twins.

The conjoined twins, also known as Siamese twins, are identical twins joined In utero (in the womb). It happens in 1 of 200.000 newborns, mostly in women (75%) and their survival rate is between 5% and 25%.

The name of Siamese twins comes from Chang and Eng Bunker, Thai brothers born in Siam (now Thailand). They travelled with P.T.Barnum circus, and they were joined by a band of flesh, cartilage and their fused livers at the torso. They were not only showed as "monsters", but also as good skilled acrobats and magicians, as well as good in business matters.

Chang and Eng Bunker. Picture from fineartamerica.com

Now we know what conjoined twins are, why does it happen?

Identical or fraternal twins?

They are so similar... but are they really the same? Today we are going to speak about the difference between identical and fraternal twins.

First of all, a twin is one of two offspring in the same pregnancy. The main difference between identical and fraternal twins is that identical twins come from the same zygote that is divided in two different embryos, and fraternal twins come from two different zygotes fertilized by two different sperm cells.

Twin differences. Picture from www.genomesunzipper.org

Ok, until now it seems easy, more or less. But in real life, what can make us differentiate between both types of twins? Here some clues: