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.
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