It is believed that the twins - are brothers or sisters who were born in the same time as the two drops similar to each other.
In turn, the twins are called those who are different in appearance and gender. As for the doctors, they are only a condescending smile, hearing this judgment.
After all, in medicine called twin children born in a single pregnancy.
However, the difference between different types of twins still available.
Biological features of the twins
The appearance of light twins - a process that is not yet fully understood by modern medicine. At present there are 3 options for the development of multiple pregnancy, after which the twins are born.
The first option - the egg after fertilizationone sperm begins to divide by 2, 3 or more parts. Later-born babies are called monozygotic or identical twins. This pregnancy can develop in different ways: general for fruit and fetal bladder platsenta- each fruit has its own bag of waters, but they have a common platsenta- each fetus and its placenta bubble.
The second option - monozygotic (poluidentichnye)Twins. This is a fairly rare event. The process of the emergence of such a pregnancy is complicated. The egg before fertilization has a polar body, which must then wither away. If not, it can also develop a pregnancy. Moreover, in this case the polar body and the egg may be fertilized or one or more sperm.
As for dizygotic twins, theyborn when two eggs are fertilized 2 sperm. The percentage of genes in such coincidence is 50% twins. Each of these fruits has its own bag of waters and its placenta.
External features of the twins
Identical twins, who have the samea set of genes is very similar in appearance. However, the similarity with the mirror born only a small percentage (about 25%) of these children. All identical twins have the same blood group, but the majority - and even fingerprints. Identical twins are born only of the same sex.
A curious feature of poluidentichnyh twins -at their outer similarity, they can have a different sex. Dizygotic twins, which is popularly known as twins, are similar to each other as much as ordinary siblings. They can be the same sex and opposite-sex.
How are the twins of twins
Thus, it can be summarized that the difference between twin twins is as follows:
From a medical point of view, the twins are all the children born in a single pregnancy. That is, these are like twins and triplets.
The twins differ in the type of fertilization: poluidentichnye, monozygotic and dizygotic. Poluidentichnymi are superficially similar twins, but they may be identical raznopolymi- - superficially similar and one pola- dizygotic - twins apparently different from each other.