Down syndrome is characterized by which chromosomal abnormality?

Down syndrome is caused by the presence of an extra chromosome 21, leading to the condition known as trisomy 21. This chromosomal abnormality can occur due to nondisjunction during meiosis, resulting in gametes with an extra copy of chromosome 21. When one of these gametes fuses with a normal gamete, the resulting individual has three copies of chromosome 21 instead of the usual two.

Individuals with Down syndrome often present with a distinct set of physical features and varying degrees of intellectual disability. Early intervention and various support systems can significantly enhance the quality of life for those affected.

In contrast, the other options represent different chromosomal abnormalities: trisomy 18 (Edwards syndrome) and trisomy 13 (Patau syndrome) are associated with significantly more severe developmental issues and typically result in shorter life spans, while monosomy X (Turner syndrome) occurs in females and is characterized by the absence of one of the X chromosomes. Thus, understanding the specific chromosome involved is critical in identifying and studying the respective conditions.