Final answer:
Trisomy 21 is the most common autosomal aneuploidy leading to Down Syndrome, which is viable because it involves a smaller chromosome.
Affected individuals feature distinct physical characteristics and developmental delays, and the condition occurs more frequently with increasing maternal age.
Step-by-step explanation:
The most common form of autosomal aneuploidy is Trisomy 21, which leads to Down Syndrome. This condition is viable because the extra genetic material associated with the smaller chromosome 21 does not disrupt vital developmental processes as much as extra genetic material from larger chromosomes would. As a result, individuals with this condition can survive to birth and often to adulthood.
However, they typically display characteristic physical features such as short stature and stunted digits, a broad skull, and large tongue, as well as developmental delays. The likelihood of a fetus being conceived with Down Syndrome increases with maternal age, as older women are more likely to produce eggs with improper chromosome separation, resulting in nondisjunction.