I was surfing around the internet the other day and came across the Quintessential Quintuplets manga, which has an anime currently airing. Its harem comedy humor isn’t really my thing, but I might watch it if it gets an English dub at some point. What did interest me was that we learn that the quintuplets are monozygotic quintuplets, so what exactly does that mean and what does it have to do with twins and other instances where there are multiple births, aka the mother has more than one child at once? Now since we are going to be talking about births and babies let me quickly get some terms out of the way.
Fertilization is the process where the male sex cell or sperm, fuses with the female sex cell, or egg. Each of the cells contains 1 copy of chromosome #1 through #22. The egg also contains an X chromosome while the sperm will contain either and X or a Y. When the sperm and egg fuse, they create a cell called a zygote.
It is the zygote that then develops into the baby, which typically takes about 9 months.
Normally we humans have 1 child at a time, but there are instances of multiple births where more than one child is born at the same time. The most common type of multiple births is twins, which are not all that common. In the USA the likelihood of having a twin is around 16.7 twins per 1000 births according to a 2012 study. However, interestingly enough the Yoruba people of western Africa have around 100 twins for 1,000 births. Now there are some genetic traits involved in twins as women who have a family history of having twins are more likely to have twins. However, in the case of the Yoruba people, it is thought that their diet plays a large role in their high rate of having twins. This is because the species of yam that is native to western Africa is high in phytoestrogen (plant estrogen), which is theorized to affect female physiology regarding childbirth, at least according to studies done in 1995 and 2008. On the opposite end is southeast Asia, which has a very low rate of twins at 9 twins for 1,000 births.
Next there are triplets where three children are born at the same time, and I had to do a bit of digging to find some data on the chance of having triplets. The chance of having triplets or higher numbers of multiple births in the United States in 2017, according to the CDC, was 0.33 sets of triplets or more per 1,000 births. Additionally, the rate appears to be decreasing since at least 2010 according to the data. Now for the big question: how do multiple births happen?
Normally the mother only releases 1 egg at a time, and that one egg is fertilized, leading to the child that is then born after 9 months. However, sometimes the mother can release more than one egg at a time, and it is possible for both eggs to be fertilized, leading to two or more zygotes, and multiple births depending on the number of eggs released.
2 eggs = dizygotic twins
3 eggs = trizygotic triplets
It is possible to have more, but as you saw in the previous section it is highly unlikely. In any case what you might scientifically call Dizygotic twins, we commonly refer to as fraternal twins. In layman’s terms they are siblings that are born at the same time. They can both be the same sex, or be one of each. For an anime example we have Johan and Anna from the Japanese psychological thriller, Monster.
Mono means 1and monozygotic means 1 zygote which is the norm in human reproduction, so how do you get two or more children from 1 zygote? To answer that I need to briefly touch on the initial stages of human development. After the egg is fertilized and becomes a zygote, it begins to divide; 1 cell becomes 2, 2 becomes 4, and so on. This continues until the zygote becomes a morula, or ball made up of around 200-300 cells.
The morula then undergoes a transformation where a cavity forms inside of it, becoming a blastocyst. Now the reason that I had to go over this is to explain where monozygotic or identical twins come from. During the early stages of development, it is possible for the morula and/or blastocyst to actually divide in half, forming a completely new morula or blastocyst.
As we can see in the diagram because of the split happening during the early stages of development monozygotic twins are identical because they share the same DNA, hence the name identical twins. We can see this with the Hitachiin twins from Ouran Highschool Host Club.
Warning Extra Science Content
Twins are often used in various biological disciplines like psychology to look at whether a particular phenomenon is caused by genetics, the environment, or some combination of the two. Fraternal twin studies can be used to determine the extent to which genetics influences a particular trait, because theoretically the twins being born at the same time would share near identical environments. On the other hand, identical twins, especially twins separated at birth can be used to determine the extent the environment influences a trait as they would be genetically identical. NASA actually performed their study of how long-term space flight affects the human body using the identical twins Mark and Scott Kelly.
Extra Science Content Over
Triplets and Quadruplets
When it comes to triplets or even higher numbers of multiple births, they can be completely monozygotic, completely dizygotic, or some combination of the two. As previously stated, triplets are much less common, especially monozygotic triplets where the embryo splits three times. However, we do see them in anime and my example today is the Chi-chans from A Centaur’s Life.
Quadruplets can also be monozygotic or dizygotic and are even more rare than twins or triplets. I do remember reading an article last year about a woman who had identical fraternal twins. Now you might be thinking but wait I thought you said identical and fraternal twins are two completely different things. And the answer is yes, identical and fraternal twins are different things, but this will make sense in the end. The mother was going to have fraternal twins, but then each fraternal twin split into an identical twin, so 2 became 4, hence calling them identical fraternal twins. Now when it comes to anime I could only find one example of quadruplets, Syaoran Li’s sisters from Card Captor Sakura.
Neither the anime or manga gives any information as to whether they are monozygotic or dizygotic quadruplets, but I think I can safely say that they are dizygotic twins. This is because they do not share the same eye color, despite otherwise looking nearly identical. Also, I know that certain environmental factors can cause eye color to change with age, which could explain their different eye colors. However, we know very little about the sisters, so I would not want to speculate any further on that.
Yes, it is possible to have quintuplets naturally without the help of modern medical technology. However, they are very rare and many times not all of the children survive infancy. This is due to the fact that they are born prematurely. The first set of recorded quintuplets known to have survived past infancy were the Dionne quintuplets, who were born 2 months premature in 1934. Additionally, the quintuplets were monozygotic or identical. Now when it comes to the odds of having quintuplets, I couldn’t find any sources I would completely trust for scientific data. One website said that while having quintuplets is possible, calculating the odds is impossible due to how rare they are, which makes sense to me. Long story short, yes monozygotic quintuplets are possible, but the odds are very, very, low.
Now this brings us to the Quintessential Quintuplets, who are stated in the manga to be monozygotic and it is entirely possible according to real world science.
But, wait a minute, you said that Syaoran’s sisters were dizygotic because of their different eye colors and the Quintessential Quintuplets all have different hair colors.
That is a fair point but in the manga the Quintessential Quintuplets all share the same hair color most of the time and the manga tells us that they all have the same hair color. The hair colors were probably changed for the anime as a way for us to easily tell the quintessential quintuplets apart from one another.
I hope that you enjoyed my explanation of multiple births and yes, the quintessential quintuplets are entirely possible. So, I will be calling this one confirmed.