JFSOCC t1_j50r6a8 wrote on January 19, 2023 at 4:31 PM

Reply to comment by dkysh in Given that reproduction is difficult or impossible when both animals have different numbers of chromosomes, how did so many species evolve to have so many different numbers of them? by MercurioLeCher

So are people with down syndrome a form of speciation?

dkysh t1_j50ssc6 wrote on January 19, 2023 at 4:41 PM

If we were bacteria, yeah, sure. But we are extremely complicated multicellular organisms. A whole genome trisomy screws up the balance of gene expression to such an extreme that most trisomies are simply lethal and never observed (they end up in miscarriage).

A gene fusion is a less drastic event, where 2 chromosomes happen to be connected, but the genetic load is identical.