When many people hear the word “twins” they automatically think of identical twins. But fraternal twins are actually much more common, making up approximately 75% of the twin population.
For a quick refresher, fraternal twins occur when two separate eggs are released and fertilized by two different sperm. Identical twins occur when a single fertilized egg splits in two to form two babies.
Though fraternal twins are much more common than identical twins, many people don’t know much about them. Here are some facts about fraternal twins that may surprise you.
Fraternal Twins Can Be Conceived as Much as 24 Days Apart
Fraternal twins generally are conceived one of two ways – when the mother releases more than one egg during her cycle or when the mother experiences another cycle and releases an egg after she is already pregnant, which can occur up to 24 days after the release of the first egg. For this reason, fraternal twins can be conceived a few weeks apart, though they generally will be born at the same time.
Fraternal Twins Can Have Different Fathers
Because fraternal twins are conceived by two separate eggs being fertilized by two different sperm, sometimes days or even weeks apart, it is possible for fraternal twins to be fathered by sperm from two different men.
Though Not Identical, Fraternal Twins Do Sometimes Look Remarkably Alike
Scientifically speaking, fraternal twins are no different than any other pair of siblings, sharing 50% of their genes. But sometimes fraternal twins of the same gender can look remarkably alike, leading people to assume that they are identical twins. An example of this can be found in famous sisters Mary Kate and Ashley Olsen, who most people assume are identical twins when they are, in fact, fraternal twins.
Fraternal Twins Can Run in Families
It is believed by many scientists that a predisposition to release more than one egg can be genetically inherited, which is why many people will notice a family history of fraternal twins. In fact, female fraternal twins have a 1 in 17 chance of conceiving fraternal twins themselves. Also, once a woman has given birth to one set of fraternal twins she is three times more likely to conceive a second set.
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