Why does Down syndrome cause the facial structure to be almost identical regardless of the parents’ genes?
In: Biology
Have you ever inflated a rubber glove? With just a little air the glove looks like a hand, but the more air you add, the more it distorts as the palm fills but the fingers don’t.
Down syndrome happens when a person has an extra chromosome. Everyone has two of every chromosome, which means two copies of every gene. Someone with down syndrome has three copies of a small set of genes; the third copy is on that extra chromosome. As a result, those genes get expressed too much, resulting in the familiar features that seem to hide or overshadow the features that would make them more “normal”. We all have these features, but in most of us they’re toned way down. Their gloves have more air in them than ours.
Edit: Many of you have correctly pointed out that DS people do not “all look the same”. They have similar features explained by genetics, yes, but so do various ethnicities. Unfamiliarity can make it difficult for an “outsider” to tell the differences between individuals, but those differences are not only there, they are as stark as the differences between two random French people, or two random Han people.
It doesn’t look identical. Your brain is just not trained to be able to detect the minute differences in faces you aren’t familiar with.
Same reason people who have not been exposed to white people, will believe they all look almost identical. Same with Asian people. Same with black people.
Same with animals.
Someone who grew up around horses will be easily able to tell same colour horses apart just by looking at their heads.
Someone who grew up around dogs or cats or chimps will be able to do the same.
They do have faces that are different to the average face, due to the excess genetic material. But the differences in facial shape between two white peoples with downs are not any less than between two white people without
It’s worth noting that people with Down’s Syndrome don’t actually look almost identical. There’s great variation in how they look. They share similarities sure, but they don’t look identical.
What is happening there is that you notice the features of Down’s Syndrome and therefore don’t notice the things that make them different. It’s because of a lack of familiarity of people with Down’s Syndrome. The same way as if there’s any group of people with whom you’re unfamiliar you may think they all look the same, because your brain focuses on their shared features that are unfamiliar to you and therefore doesn’t clearly see the differences.
Random: When i was really young and saw someone with Down’s Syndrome I remember thinking like wow that first person [with Down’s syndrome] I saw must have a LOT of cousins bc I swear I see someone related to them everywhere I go 😭
(I hope it’s clear the joke is on me here but if this is offensive no worries will take this down)
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