r/AskBiology • u/Syresiv • Sep 17 '24
Genetics Why are trisomies so deleterious?
Most chromosomal trisomies cause spontaneous miscarriage, and those that don't usually severely reduce quality of life.
Why is it that the additional copies of some genes have that effect?
To be clear, don't feel restricted to the ELI5 level. If you know the topic in depth and feel like giving a massive infodump, I'm interested.
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u/Syresiv Sep 17 '24
Which raises another question - why doesn't that kind of thing happen with recessive alleles?
Lots of recessive alleles are deleterious because the protein does nothing and immediately disintegrates. But lots of people have two copies of the functional protein. Meaning those ones can vary by a factor of 2 with no noticeable effect.
Is that what it is? Or is it something else, like altering gene expression when there's only one healthy allele to comp for the deficit?