From the moment I was born, I was never alone. About three months into my mom’s pregnancy she discovered that she was having twins. Now when people hear the term “twins” most automatically jump to mental image of two identical looking people with the same features and personality. However if you have ever met a pair of twins, you know that in most cases that could not be more wrong. Take my twin sister and I. If you were to look at the two of us you would see my sister with long straight blonde hair and narrower features like my mom and me who has long curly red hair with rounded features just like my dad. Now people can usually conclude that we are sister’s due to some shared features, but most are shocked to learn the fact that she is a mere 60 seconds older than me.
As most of you probably already know, twins are categorized as either fraternal or identical. This relates to the way in which the egg either splits, creating two identical halves or two eggs are fertilized at the same time. As you can probably conclude from my earlier description of my sister and I, we are fraternal twins. As described in an article on Very Well fraternal twins share about 50% of the same genetic makeup, which happens to be the same amount as any other pair of siblings. This means that fraternal twins are no more similar than other siblings. So while we may share the same birthday, that is truly the only thing distinguishing my sister and I from any other set of siblings.
The occurrence of fraternal twins can actually run in the families due to the hereditary influence. Hyperovulation relates to the condition in which a woman releases more than one egg every cycle. As I said earlier, fraternal twins occur due to the fertilization of more than one egg, so with hyperovulation, the probability of more than one egg being fertilized is greater. This gene can in fact be passed down to a daughter, which therefore increases her likely hood of having fraternal twins. Since the trait is carried on the X chromosome men also have the ability to pass the trait on to their daughters. However the chances of fathering a set of fraternal twins are not increased if a man is a carrier of the gene, only if the mother possess it. This phenomenon is the reason behind the assumption that twins tend to skip a generation.
Two twin facts that may come as a surprise is that fraternal twins can actually be conceived at different times and fathered by two different men. Now you may be asking yourself “How is that possible?”. As I previously disclosed earlier in my blog post, fraternal twins result from the fertilizing of two separate eggs so there is a possibility that after one is fertilized another one is as well days later from other sexual relations. This incredible phenomenon of twins being conceived days apart from each other is referred to as superfetation. Also relating to that discussion if the eggs were fertilized by two different men than the eggs would have different fathers. Superfecundation is the name behind this phenomenon. Twins are not as simple as one may believe.