My brother looks almost exactly like my dad, but I don’t think I look anything like either of my parents. What determines how much I look like my parents?
– A middle school student from Virginia
August 8, 2019
Excellent question! What determines all the parts of our physical appears is not entirely known yet, but there are a few things we do understand about why we look the way we do.
DNA: the instructions to make us who we are
Every living thing (including us) has a tiny instruction manual inside us, called DNA. All people have some DNA that’s the same: we all grow 4 limbs, a heart, skin, a brain, and all the other standard parts of being a person. But we don’t all have exactly the same DNA instruction manual. This is why we don’t all look like the same person!
It’s kind of like if you were building a house by following an instruction manual. Let’s say your friend is also building a house, but they have a slightly different version of the instruction manual. You would both end up with a house, but they could end up looking very different!
At this point you might be wondering, if we all have slightly different instruction manuals, why do we sometimes look like our parents or relatives? The reason is because our instructions actually come from our parents!
We all inherit half of our DNA instructions from our mom and half from our dad. Your instructions are a mixture of the instructions your parents’ gave you. Your sibling’s DNA is also half from mom and half from dad. But it is a slightly different mixture from yours (unless you are identical twins)!
How we can get different combinations of genes from our parents?
Imagine your parent has a jar filled with candy. You get to pick three pieces of candy from parent’s jar, one of each type of candy – a lollipop, a candy cane, and a life saver. The purple jars below show all the different combinations of candy that you could get.
This is the same reason we can get have different combinations of DNA instructions from our siblings. Both you and your sibling pick candy from your parents’ jars, but the ones you get can be different from each other.
How does DNA make us look the way we do?
How your DNA instruction manual determines how you actually look is a little complicated. Different aspects of our appearance, like eye color or ear lobe shape, are called traits. Sections of DNA that are dedicated to a specific trait are called genes.
We all have the same genes, but they can come in slightly different versions. For example, in my DNA instructions, a gene for eye color says I have blue eyes. You may have a different version of that gene that says to have brown eyes.
So for each trait, we have some subset of the instruction manual that dictates what that trait will look like.
But it gets even more complicated! Some of the traits that are involved in physical appearance are determined by multiple genes.
For example, there are four genes that contribute to the size and shape of your forehead. There are five that say how the tip of your nose will look. And five more that are involved with how wide your face is.1 Different combinations of genes for one of these traits create a bunch of different physical attributes.
And on top of that, your parents may have multiple versions of each of these genes! The version that you get can be totally different from the version your sibling gets.
All of the different combinations of these genes come together to determine how you look. Even though we get all our DNA from our parents, each of us has a unique combination of genes. Sometimes that means we don’t look like them at all.
There are tons of genes that shape our appearance. The words next to each facial feature are just a few genes that have been shown to be involved in that aspect of appearance. There are many more that we already know about and even more that we haven’t figured out yet.
Figure adapted from Wikimedia
Is it all written in our genes?
What makes the genetics of our appearance even more complex is that your environment can change the way we look too! Spending time in the sun can make your skin darker, your hair lighter, or cause freckles. Getting enough food and vegetables can help you grow taller.
On top of that, your genes and your environment can work together to contribute to how you look as well! Some things that you are exposed to in your environment can cause certain genes to be turned on or off or even tune them to a specific level.
Because of this, even if you and your sibling are identical twins and have identical DNA, you would still look slightly different.
There are a lot of different things that determine how much we resemble our parents and what we look like. That’s what makes genetics of complex traits, like appearance, so interesting to study! Even with everything we know about the genetics of complex traits, there are still so many questions left to answer.
By Kelsey Fryer, Stanford University