Eli5: Why does the one extra chromosome cause Down syndrome?

Question

Why does the addition of one extra chromosome cause Down syndrome, and how come that people of all backgrounds with Down syndrome have the same distinct features? How does the addition of one extra chromosome cause Down syndrome?

In: 27

Answer 1

Chromosomes are what cells use as blueprints to make stuff. More of those chromosomes means more of that stuff. Body functions are like baking recipes. If you dont stick to the recipe exactly, but instead use too much of some ingredients, things will go wrong.