Why is an extra chromosome worse? Where does this extra chromosome come from?

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Shouldn’t I like have 3 hands instead of 2 if I have an extra chromosome?

In: Biology

Let’s imagine we’re building a tower of bricks, our architects are those chromosomes. Let’s now imagine a new random architect joins the team and thinks it would be cool to build a tower horizontally in the middle of your original tower.

The tower will have problems staying upright thanks to that new architect

Not a biologist, and I am formulating a theory that an expert can destroy: A missing or severely malformed chromosome will prevent the development of a body, because vital functions do not exist. An additional chromosome can disturb cell operation in the whole body, but the others still function more or less, so the fetus may survive. It is easy to diagnose. Small damage to a functional chromosome (that is usually caught by the DNA’s redundancy) can affect single functions/molecules that may or may not have a severe effect, perhaps restricted to specific types of cells/tissue/locations.

All the info needed for a human organism to function is encoded in human DNA and neatly packed in 46 chromosomes. Just like a recipe for a cake – 500g of flour, 4 eggs, 200 g of butter etc etc etc. If you add more information (extra genes in another chromosome), you mess up the recipe – some of your cells will be producing proteins they weren’t meant to produce, some will be confused by the new stuff and won’t do what they need to do etc. Imagine adding 3 more eggs in your cake – it’ll lose structure and you’ll get soup; or adding more flour – you won’t get cake, you’ll get a brick…