Fraternal twins are those kinds of twins who are dizygotic which means that they have developed from two different eggs that have been fertilized by two different sperm cells. Identical twins on the other hand are those twins who are monozygotic which means that they are developed from a single fertilized egg that split.
Besides the differences in definition and method of development, there are many other differences between identical and fraternal twins and the following are some of the main ones:
- One of the main differences between identical and fraternal twins is that identical twins are always of the same gender whereas on the other hand fraternal twins are usually of the different gender.
- Another main difference between these two types of twins is that the genetic code in identical twins is nearly identical whereas the genetic code in fraternal twins is like any other sibling which is not identical.
- In the case of identical twins, the blood type is always the same but in case of fraternal twins, the blood group or type of the twins may be different.
- The causes which are responsible for identical twins are still unknown but on the other hand, the causes of fraternal twins are hereditary predisposition, use of certain fertility drugs and IVF treatment.
- In case of fraternal twins, the appearance of the twins is as similar as any other pair or set of siblings but as the name suggests, identical twins look extremely similar, though due to some environment factors, they may begin to look slightly different from one another.
- The risk of TTTS or twin to twin transfusion syndrome in the case of identical twins is higher than in the case of fraternal twins and this is yet another difference between the two.
- The likelihood of birth of identical twins is uniform throughout the world and is about 3 in 1000 which means that about 3 of every 1000 twins are identical. But in the case of fraternal twins, the likelihood varied from country to country. The likelihood is over 20 per 1000 twins in some parts of Africa but is only 6 per 1000 twins in Japan. Two thirds of all twins in the world are fraternal.
- In the utero, identical twins may be contained in one sac but on the other hand, fraternal twins develop separate sacs.
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