You Twins they are born from an embryological phenomenon, where the pregnancy of a mother results in the formation of two (or more) children instead of one, called twin pregnancy.
In other words, these are fertilizations that generate two or more embryos. However, three (triplets), four (quadruplets), five (quintuples), six (sextuples), seven (sevenfolds) or eight (octuplets) children may be born.
Generally, the delivery of twins is a caesarean because of the position of the babies and they can be born at different times.
The formation of twins can occur in two ways, that is, if they are born identical they are monozygotic, if they are born with different physical characteristics, they are dizygotic.
Many stories revolve around this type of training, for example, the sensations they share throughout life.
Types of Gemini
There are two types of twins:
1. single-egg twins
One-egg (monozygotic) or true twins are those who are born identical and therefore are always of the same sex.
For this to happen, a single egg is fertilized by a single sperm with subsequent division of the zygote (egg cell), where the egg divides thus forming two (or more) embryos.
These twins with physiognomic similarity have the same genome (DNA), thus, clones of each other, in addition to sharing the same placenta (only 10% to 15% of identical twins have placentas separated). However, they have different fingerprints and personalities.
Some complications can occur with the division of the egg of monozygotic twins, which stops in the middle of the cell division process and the embryos end up fusing, resulting in the sharing of body parts (be it head, trunk, buttocks or limbs) and often organs internal.
This very rare event is called conjoint twins, associates, xyphopagus or Siamese, however, with the advance of medicine, nowadays many of them can be separated.
2. fraternal twins
Fraternal twins (dizygotic) or multivitelline twins are those who are born with different appearances.
Also called fraternal or false twins, they are generated by two eggs and two sperm and, therefore, are dizygotic (they have two zygotes or egg cells), forming two embryos.
It is interesting to note that they can have different sexes, that is, a girl and a boy are born.
Unlike identical twins, these can show about 50% identification between the genomes where they are usually developed by two amniotic sacs and two placentas.
know more:
- How does human fertilization occur?
- Phenotype and genotype
- Cloning
- human genome project
