Down syndrome is caused by trisomy of which chromosome?

Down syndrome is caused by trisomy of which chromosome?

• A. Trisomy 18
• B. Trisomy 21
• C. Monosomy X
• D. Trisomy 13

Answer: (B)

Down syndrome is caused by having three copies of chromosome 21, instead of the usual two. This extra copy adds genetic material that disrupts development and leads to the characteristic facial features, growth patterns, and intellectual disability associated with the condition. The extra chromosome usually arises from nondisjunction during the formation of eggs or sperm, with maternal age being a known risk factor. Other chromosomal conditions involve different chromosomes, such as trisomy 18 or trisomy 13, which produce their own distinct syndromes, or monosomy X (Turner syndrome), which is not related to Down syndrome.

Down syndrome is caused by having three copies of chromosome 21, instead of the usual two. This extra copy adds genetic material that disrupts development and leads to the characteristic facial features, growth patterns, and intellectual disability associated with the condition. The extra chromosome usually arises from nondisjunction during the formation of eggs or sperm, with maternal age being a known risk factor. Other chromosomal conditions involve different chromosomes, such as trisomy 18 or trisomy 13, which produce their own distinct syndromes, or monosomy X (Turner syndrome), which is not related to Down syndrome.