The biology of twins and the twins
The twin phenomenon of modern medicine can't explain until the end. There are three options for the development of pregnancy, leading to their emergence. In the first case, the egg begins to divide after fertilization, one sperm into several parts. Born as a result of identical or monozygotic twins who during gestation had or shared placenta and amnion, or a separate placenta and the fetal bladder.
Also, each twin may develop in their fetal bladder with the placenta shared with your brother/sister.
The second option or polyidentities are monozygotic twins who are born very rarely and as a result of complicated pregnancy. The polar body of the egg usually dies before fertilization, however, in this case this does not happen, and after hitting one or two of sperm, it develops a second child.
And finally, the third variant – the birth of dz twins is possible when fertilization of two ova by two sperm. Such twins are the same set of genes about 50% during pregnancy developing in separate bubbles and fetal placentas.
Exterior features twins of twins
So, what is the difference between twins and twins? The most similar appearance are identical twins with the same set of genes. They have the same blood group, gender and fingerprints. It so happens that a certain number of identical twins (approximately 25%) is born with an interesting difference – the mirror likeness.
The mirror similarity of the full similarity identical twins, which look completely replicates the appearance of each of them.
Polyidentities (monozygotic) twins despite the external similarity can be born heterosexual, whereas dz twins, which are twins, similar as ordinary children of the same parents. Also twins can be different sexes and same-sex.
According to the medical point of view, twins are twins, and triplets – in other words, all children born in one pregnancy are considered to be twins. The main difference is determined by the type of fertilization (monozygotic, polydentate, dz) and the external similarity – the most similar twins, and twins vary in appearance, having similar external features.