Why do you think that monosomy or trisomy of the autosomes are more detrimental to survival than monosomy or trisomy of the sex chromosomes?
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1) The Y chromosome is very small, and contains few genes, and most of the genes it does contain are genes that masculinize a fetus - they aren't essential for life. After all, 50% of babies are born without any Y chromosome.
2) All but 1 X chromosome is inactivated per cell. In females with a normal XX sex chromosome set, every cell has 1 X chromosome inactivated (they are called Barr bodies), leaving only 1 active X chromosome. If a female has XXX or XXXX, then all of them except for 1 is still inactivated. Inactivation is not 100%, so having XXXX is not identical to having XX, but it is close.
2) All but 1 X chromosome is inactivated per cell. In females with a normal XX sex chromosome set, every cell has 1 X chromosome inactivated (they are called Barr bodies), leaving only 1 active X chromosome. If a female has XXX or XXXX, then all of them except for 1 is still inactivated. Inactivation is not 100%, so having XXXX is not identical to having XX, but it is close.