Final answer:
Every trisomy except for Trisomy 1 has been found in spontaneously aborted human embryos. Trisomy refers to having an extra chromosome, and while most autosomal trisomies result in miscarriage due to severe gene dosage imbalance, trisomies of smaller chromosomes like 21 can result in live births and survivors into adulthood, as seen in Down Syndrome.
Step-by-step explanation:
Spontaneously aborted human embryos have been found to contain every trisomy except Trisomy 1. In the context of aneuploidy, trisomy refers to individuals who have a genetic makeup with three copies of a particular chromosome instead of the normal two. For instance, Down Syndrome is a result of trisomy 21, where an individual has an extra, third copy of chromosome 21.
The concept of gene dosage highlights why having the extra chromosome can be problematic. In general, most autosomal trisomies, where autosomes are chromosomes other than the sex chromosomes X and Y, do not result in a viable birth, typically leading to miscarriage. This is because each chromosome carries many essential genes, and having an extra set of these genes disrupts cellular and overall biological functions.
However, certain trisomies involving the smaller chromosomes, like 13, 15, 18, 21, or 22, have been documented in live births. Trisomy 21 is the most common trisomy that can result in live births and typically persists into adulthood, albeit with varying degrees of developmental and physical challenges. Notably, individuals with larger chromosome trisomies, such as trisomy 1, do not typically survive; hence embryos with trisomy 1 are not seen among spontaneously aborted pregnancies or live births, making it unique among other trisomies in its complete incompatibility with survival.