What congenital disorder is caused by having an extra chromosome 21?

• A. Turner Syndrome
• B. Down's Syndrome
• C. Klinefelter Syndrome
• D. Fragile X Syndrome

Answer: (B)

The condition characterized by the presence of an extra chromosome 21 is known as Down's Syndrome, also referred to as trisomy 21. This genetic disorder results from an error in cell division, leading to the presence of three copies of chromosome 21 instead of the usual two. The additional genetic material impacts development and can cause a range of physical and intellectual disabilities.

Individuals with Down's Syndrome often exhibit distinct physical features, such as a flat facial profile, slanted eyes, and a single transverse palmar crease, as well as varying degrees of developmental delays and learning challenges. Early intervention, education, and supportive therapies can significantly improve outcomes and quality of life for those affected by this condition.

The other disorders listed are not associated with an extra chromosome 21. Turner Syndrome, for instance, arises from a missing or incomplete X chromosome, Klinefelter Syndrome occurs due to an extra X chromosome in males, and Fragile X Syndrome is a genetic condition caused by changes in the FMR1 gene on the X chromosome. Thus, the unique association of Down's Syndrome with an extra chromosome 21 makes it the correct answer to the question.