The difference between identical and fraternal twins

Before we start explaining the differences between Identical and fraternal twins let’s start with a short explanation of the origin of both words.

Etymoligically, both terms have the same origin (Latin gemellicium) and are related to the birth of two children at the same time. The only difference was in the use of the term. Over time, the difference between the two terms has become distinct with the change in advances in genetics and knowledge related to the development of human embryos. In the last edition of the RAE technical dictionary, a precise differentiation of the two words is given:

Definition of identical and fraternal twins

  • Identical twins: Were born at the same time and originate from the same egg cell.
  • Fraternal twins: Were born at the same time and originate from two different oocytes.

What is an identical twin?

We speak of fraternal twins when different eggs and sperm have fertilized and the resulting children are born at the same moment, d.h. that they are siblings but otherwise no special feature occurs.

What is a fraternal twin?

However, identical twins are genetically identical because they come from the same egg and sperm and have split at a very early stage and developed individually. For this reason identical twins share the same DNA and therefore the same sex. Strictly speaking, clones. Nevertheless, it must not be forgotten that the effects of the environment can also be genetic and produce differences in twins. In fact, twins have different fingerprints. This means that they have the same "raw materials" but still develop into different individuals.


In gynecology identical twins spoken ( monozygotic, from one egg and one sperm cell, which divide into two) and fraternal twins (dizygotic, from different eggs and sperm). Regardless of their origin, in twin pregnancies, each fetus has its own placenta, amniotic sac and chorion (egg skin). Twin pregnancies can be monochorial and bichorial. In identical twins, both can be the case.

How many pregnancies are statistically identical or fraternal twins?

Statistically 1 out of 80 pregnancies are twins , where two thirds are identical twins and one third are fraternal twins. It is believed that the number of twin pregnancies is even higher, but the development of an embryo stopped at an early stage of pregnancy.

There are both environmental factors (z.B. Nutrition) as well as hereditary factors that can lead to a twin pregnancy. The use of assisted reproduction treatments is a key factor in increasing the incidence of twin pregnancies, as more than one embryo is often used.

Also worth noting, is the importance of twins in biomedical research, as they provide clues to the origin or predisposition of certain genetic diseases give.

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