What is the name for the genetic condition characterized by an extra chromosome 21?

• A. Turner syndrome
• B. Down syndrome
• C. Klinefelter syndrome
• D. Huntington's disease

Answer: (B)

The genetic condition characterized by an extra chromosome 21 is known as Down syndrome. This condition, also referred to as trisomy 21, occurs when an individual inherits three copies of chromosome 21 instead of the usual two. This extra genetic material disrupts the normal course of development, leading to a range of physical and intellectual disabilities.

Individuals with Down syndrome often exhibit distinct physical traits such as a flat facial profile, slanted eyes, and a single transverse palmar crease. Additionally, they may experience various health issues including heart defects and increased susceptibility to certain medical conditions. Early intervention and educational support can significantly enhance the quality of life for those with Down syndrome.

In contrast, the other options refer to different genetic conditions. Turner syndrome involves a missing or incomplete X chromosome and primarily affects females, while Klinefelter syndrome is associated with an extra X chromosome in males. Huntington's disease is a neurodegenerative disorder caused by a specific genetic mutation, unrelated to chromosomal abnormalities like those seen in Down syndrome.