Doctors disprove the occurring opinion that twins are brothers or sisters with identical appearance who were born almost in at one time at one mother whereas the twins who were born under similar conditions differ externally and have a different floor. It appears, all children born in one pregnancy are twins. However, some difference nevertheless is available.
Features of biology of twins and twins
The modern medicine cannot explain a twin phenomenon up to the end. There are three options of development of pregnancy leading to their emergence. In the first case the ovum begins to be divided after fertilization one spermatozoon into several parts. As a result identical or monoovular twins who at incubation had or the general placenta and a fetal bubble, or on a separate placenta and a fetal bubble are born.
Also each twin can develop in the fetal bubble, having at the same time a placenta, the general with the brother / sister.
The second option are monogerminal or semi-identical twins who are born quite seldom and as a result of difficult pregnancy. The polar body of an ovum usually dies off before fertilization, however in this case it does not occur, and, after hit of one or two spermatozoa, in it the second child develops. And, at last, the third option – the birth of dizygotic twins - is possible at fertilization of two ova two spermatozoa. Such twins coincide on a set of genes approximately for 50% and throughout pregnancy develop in separate fetal bubbles and placentae.
External features of twins and twins
So, what difference between twins and twins? monoovular twins with an identical set of genes have the most similar appearance. At them the blood type, a floor and fingerprints coincides. Happens so that a certain number of monoovular twins (about 25%) is born with interesting difference – mirror similarity.
Mirror similarity – full identical similarity of two twins whose appearance absolutely repeats appearance of each of them.
Semi-identical (monogerminal) twins at all external similarity can be born heterosexual whereas the dizygotic twins who are twins are similar as ordinary children from some parents. Also twins can be heterosexual, and same-sex. According to the medical point of view, twins are both twins, and triplets – in other words, all children who were born in one pregnancy are considered as twins. Their main difference is determined by fertilization type (monoovular, semi-identical, dizygotic) and external similarity – twins are most similar, and twins differ on appearance, having only similar external lines.