Fraternal twins develop when two eggs are fertilized by two different sperm. These two fertilized eggs implant in the uterus and grow. Unlike identical or monozygotic twins, who share 100% of their DNA, fraternal twins only share about 50% of their DNA. For this reason, they are not more similar genetically than the rest of the siblings, if they have any.
Twins and fraternal twins have been the subject of myths and mysteries, as well as being a source of curiosity for many. Being the result of the same pregnancy, there are curiosities that they do not share with the rest of their siblings. If you know any case of twins and you have curious questions about these myths, keep reading because we are going to see some of the most striking curiosities of the twins.
What are the most surprising curiosities of the twins?
They are the most common type of multiple birth
People have more internalized the concept of "twin", understanding with it brothers who are identical twins. It is much more striking to see two identical people than brothers of the same age who are not so similar. But in reality, identical twins are a rarity of nature, while Twin pregnancy accounts for 75% of multiple pregnancies in the world.
Their genetic structures are different
As we have mentioned before, twins appear when two sperm fertilize two different ovules. Because they are two different ovules when they are fertilized and implanted in the uterus, their development is independent. Namely, the ovum of each twin develops its own amniotic sac, placenta, and other different support structures.
They can be of the same sex… or not
As in the case of any other conception, the chromosomes of the father's sperm determine the sex of the future baby. Since fraternal twins originate from two different sperm, each of those two fertilized eggs could be a boy and a girl, or both boys or both girls. Namely, twins can be born of any of the possible sex combinations: boy and girl, two boys or two girls. Of course, we are talking from the genetic point of view. Sex is determined in the womb, while gender is a social construct and something a person decides for themselves later on.
Twins can have two different fathers.
This phenomenon is real and is called super fertilization or bipaternal twins. This happens when a woman releases multiple eggs, which is known as hyperovulation. If this hyperovulation occurs and the woman has unprotected intercourse with more than one partner, these eggs can be fertilized by sperm from two different men.
They can be born on different days
In fact, they can be born in days, weeks, or even in a different month. Suppose a woman releases an egg during her cycle and is fertilized, but her cycle is interrupted. When she reaches the next cycle, thus releasing another egg, she is already pregnant, but that second egg can also be fertilized. This can occur up to 24 days after the release of the first egg, leading to twins being born within a few weeks of each other. This phenomenon is known as superfetation.
They can be totally different
There is no unwritten law that says that siblings born from the same pregnancy have to be alike, although people often think so. But since twins only share 50% of their DNA, they can have very different characteristics and preferences when it comes to their personality. Unlike identical twins, who have a much stronger bond because they share 100% of their DNA, fraternal twins can be polar opposites. This is something that can make parenting difficult, and drive their parents crazy, to say the least.
Twins can also be hard to tell apart
This can be disconcerting. Despite all their differences, twins can be physically very similar. In many families there are siblings who are very similar due to their shared genetic makeup, but their ages are different and, therefore, it is not possible for them to be confused. In the case of twins, they are brothers of the same age and that makes it difficult to tell them apart. Because of this, it is sometimes difficult to distinguish fraternal twins from identical twins. The only accurate way to see the difference is through a DNA zygosity genetic test.