Which chromosomal abnormality is a commonly known example?

Down syndrome is a chromosomal abnormality resulting from an extra copy of chromosome 21, leading to a total of three copies instead of the typical two. This genetic condition is characterized by a distinct set of physical traits, developmental delays, and potential health issues. Down syndrome is widely recognized in both medical and public contexts, making it a prominent example of a chromosomal abnormality compared to other listed conditions.

In contrast, cystic fibrosis is caused by mutations in the CFTR gene, not a chromosomal change. Fetal Alcohol Syndrome results from prenatal alcohol exposure, which affects the development of the fetus but does not involve chromosomal abnormalities. Autism Spectrum Disorder is a complex neurodevelopmental condition with various contributing genetic and environmental factors, and while certain genetic components may be involved, it is not classified as a chromosomal abnormality. Thus, Down syndrome stands out as the quintessential example of a chromosomal abnormality.