Final answer:
Spontaneously aborted human embryos have been found to contain every trisomy except for chromosome 1, as such an aneuploidy is incompatible with life and thus results in miscarriage.
Step-by-step explanation:
Spontaneously aborted human embryos have been found to contain every trisomy aside from that of chromosome 1. Chromosomes carry many genes, and abnormalities such as aneuploidy, which refers to having an abnormal number of chromosomes, can result in severe developmental issues. Specifically, every trisomy has been identified in spontaneous abortions except for chromosome 1. While trisomies such as trisomy 21 (Down Syndrome), trisomy 18, and trisomy 13 can lead to live births, with trisomy 21 being the most common and capable of survival to adulthood, the trisomy of chromosome 1 is lethal and not compatible with life, leading to spontaneous miscarriage.