[cheerfulgreek]

Originally Posted by BigRedBeta

It's not that the mother's body rejects it, it's that the having either extra information (an extra chromosome hanging out) or missing information (having only one chromosome when you should have two) results in a non-viable fetus. This would be due to having too much or too little of needed protein or some other form of imbalance that affects the growth and development.

I base this off the fact that, in humans, there are no known viable complete autosomal monosomies (Cri du Chat syndrome is a partial monosomy of chromosome 5) and only the three previously mentioned trisomies. Just because we never see individuals with monosomies or trisomies other than the ones mentioned absolutely does not mean they don't occur, but rather, that they are completely non-compatible with even advanced intra-uterine age, let alone extra-uterine viability.

Further, in humans, more than 80% of all conceptions never make it to term, and roughly 50% of all conceptions have some sort of chromosomal anomaly that makes the pregnancy non-viable. It doesn't even necessarily have to be gross chromosomal abnormalities, as significant micro-deletions of chromosomes in the right places can create a non-viable pregnancy. Most often the pregnancy is spontaneously aborted within the first 4-6 weeks and so the woman doesn't even realize she's pregnant. (Not to open a can of worms, but these facts are one of my biggest arguments against the "life begins at conception" crowd).

Thanks for this.