Are Twins Hereditary? This Study Will Blow Your Mind

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What makes us humans different from each other? The simple answer to this question is the genes we inherit from our parents. According to the Genetics Home Reference, each human carries between 20,000 and 25,000 genes [1]. Genes determine every single characteristic that you inherit: from the color of your eyes and hair to your gender itself.

Twins can exist in two ways: fraternal and identical. When more than one egg is fertilized, it means that you will be having fraternal twins. These twins may not resemble each other since they are developed from two different eggs and do not share their amniotic sac or placenta. Identical twins, on the other hand, are created when the zygote from the fertilized egg splits into two. This produces identical twins that will share their physical appearances with each other since they are genetically the same [2].

Between the two, fraternal twins seem to run in families, unlike identical twins. Your chances of having identical twins are a lot rarer since it depends on whether or not the zygote splits into two once the egg has been fertilized. This means that chances of you having identical twins are under 0.4% [3].

Fraternal twins, on the other hand, are a lot more common since it requires two eggs to be fertilized at the same time. If you are part of a family that has a history of giving birth to fraternal twins, your chances of giving birth to twins are all the way up to 14%. Although it may seem uncommon for a woman to conceive twins, her chances of having fraternal twins are a lot higher than identical twins.

Having twins depends on two major cases: the levels of specific hormones in a woman’s body and the way in which the woman’s ovaries react to the presence of these hormones in her body. Furthermore, according to the Stanford at The Tech: Museum of Innovation, women who have a history of twins being born in their families can have up to 2.5 times more chances of giving birth to twins – especially if they are cases of fraternal twins.

Genetics play a major role in determining the chances of you conceiving twins. Since it is the woman whose body releases the eggs, if the body releases one egg that splits into two zygotes or more than one egg, it is the woman’s daughter that has a greater chance of giving birth to twins. This means that men who have a history of fraternal twins in their families are not a carrier of this gene. Moreover, this gene can also be passed down to the grandchildren even if their mothers did not conceive fraternal twins. I know – it is all too complicated.

Nowadays, more and more women are opting for modern techniques of artificial fertilization such as in vitro fertilization (IVF) [4]. These techniques involve altering the levels of specific hormones in a woman’s body. As mentioned earlier, having twins depends significantly on how a woman’s ovaries react to these hormones. Therefore, the chances of conceiving twins through artificial fertilization techniques have increased enormously. Women who opt for IVF have a one in four chance of giving birth to twins [5]. This is because increasing the levels of these hormones in a woman’s body may stimulate the release of more than one egg for fertilization.

At the end of the day, identical twins are extremely rare and have nothing to do with the history of your family. On the other hand, fraternal twins are a lot more common and are hereditary.

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