As the proud parents of two identical twin boys, I sometimes look at them and wonder, are they truly identical twins? This led me down the path of doing my own research on the topic which I was keen to share my findings.
Before we talk about how identical twins can look different due to DNA mutations, it’s important to discuss the different types of twins that exist and how this matters.
What are the Different Types of Twins
We’ve written about the different types of twins in greater detail in the past but for the purpose of this post we thought it was important to highlight the different types of twins out there. This is due to a certain type of twin not looking alike and even not sharing the same sex. You’ve got two different types of twins which are:
- Fraternal or dizygotic twins – Fraternal twins are created by two separate eggs being fertilised by two different sperm cells. This creates two non-identical twins which don’t share the same DNA. As they don’t share the same DNA, they develop their own looks while having some similarity in their looks due to sharing the same parents. Due to not sharing the same DNA, they can be either boy / girl, boy / boy and girl / girl combinations.
- Identical or monozygotic twins – As the name suggests, identical twins are just that and are created by one fertilised egg splitting into two. This creates two identical babies that will share the same DNA. Due to being identical, you can only get same sex (boy / boy or girl / girl) combinations.
So going back to the title of this post what do you call twins that don’t look alike? The answer is fraternal twins due to not sharing the same DNA and developing their own looks. However with that said, fraternal twins can develop very strong similarities in their looks due to sharing the same parents. No different to how siblings of different ages can look similar even though they were born in different years.
But what about identical twins? Can they look slightly different even though they’re identical? We explore that in the next section.
How Come Identical Twins Can Look Different?
Easy answer – They get different haircuts and boom! They look different.
Serious answer – While sharing the same DNA, identical twins can have their DNA mutate differently. We know that identical twins can have birthmarks on different spots on their body or they may have different dominant hands like we’ve written about in the past. But can identical twins have more significant difference between one another beyond birth spots on their body? Yes.
Not all identical twins are necessarily identical in their looks. Take these identical twins in the UK where one twin has blue eyes while the other has brown eyes. According to the article, the twins are identical where they were formed from a single fertilised egg that was split into two but why is it that their looks are so different?
Identical twins start with the same DNA thanks to being split from one egg. However as the cell divides, DNA mutations can occur which is when you begin to see differences between identical twins. In the case of the identical twins from the UK, their DNA mutations would be specifically around their eyes and skin colour which has some slight variation.
Although we do know that eye colour does tend to darken over time. Our boys were born with blue eyes and now have hazel coloured eyes. It’s possible that these girls may end up having the same eye colour as they grow older and begin to look more identical.
Answering the question we started this post with what do we call twins that don’t look alike? Two answers:
- Fraternal twins are twins that don’t look alike. While they may look similar due to sharing the same parents, they won’t be identical like identical twins.
- Identical twins can have slight differences due to DNA mutations. These mutations can vary from birth marks to skin colour.
We hope this article has been useful and answered your question!
Thanks for reading.
My name’s Alex and I’m a husband, dad to beautiful identical twin boys, cyclist, photographer and connoisseur of great coffee!
Help I’m Having Twins has been created for me to share what I found useful as a new parent and dad to twins.