Which of the following forms of mental retardation is caused by the presence of an extra chromosome?

Correct option is A

Down syndrome is caused by the presence of an extra copy of chromosome 21, leading to developmental and intellectual delays. This chromosomal abnormality affects physical growth, facial features, and cognitive function, and it is one of the most common genetic causes of intellectual disability.
Information Booster:
1. Down syndrome is also known as Trisomy 21.
2. It affects 1 in 700 births globally.
3. Individuals with Down syndrome often have distinct physical characteristics.
4. Early intervention and therapy can improve the quality of life for those with Down syndrome.
5. Genetic testing during pregnancy can help in early diagnosis.
Additional Knowledge:
 Down syndrome: Caused by an extra chromosome 21 (Trisomy 21).
 Cretinism: Results from a deficiency of thyroid hormone during fetal development or early infancy.
 PKU (Phenylketonuria): A metabolic disorder caused by the inability to break down the amino acid phenylalanine.
 Cultural-familial retardation: A non-genetic form of intellectual disability, often linked to environmental factors.