Why are some chromosomal abnormalities (Downs Syndrome) allowed to continue through a normal pregnancy where almost all other chromosomal abnormalities are miscarried?

Question

How does the body know which chromosomal abnormality is good enough to become a person and others are better to be ended?

In: Biology

Answer 1

Some genes are more important than others. Let’s say one chromosome carries genes for some brain development and facial structure, etc. and another chromosome controls genes crucial to fetal growth and development, significant brain structure, etc. one you can live with but one you can’t.
It’s like if I went to a car factory to sabotage it. I got to an assembly line that builds the engine and break it. Can’t make the foundational parts of a car, so no car. Let’s say instead I break a machine that controls the shape of the steering wheel, still a operational vehicle, just imperfect.
People with Down syndrome are still operational human beings with the building blocks of life, just have some hurdles.