Down syndrome in humans is caused by the presence of an extra copy of which chromosome?

Correct answer: Chromosome 21

Explanation: ✅ Correct Answer: D) Chromosome 21 📚 Explanation: Down syndrome is a common genetic disorder that causes varying degrees of physical and intellectual disability. It is scientifically known as Trisomy 21 because it is caused by the abnormal cell division that results in an extra full or partial copy of chromosome 21. This excess genetic material alters the normal course of human development.