Question

Down syndrome is caused by?

1) improper migration of brain cells during brain development
2) an inherited faulty gene
3) a genetic error in which a vital enzyme is missing in the brain
4) the presence of an extra twenty-first chromosome
5) obstetric difficulties at the time of birth

Answer 1

Down syndrome is caused by the presence of an extra twenty-first chromosome, corresponding to option 4.

Step-by-step explanation:

Down syndrome, also known as Trisomy 21, results from the presence of an extra copy of chromosome 21. This chromosomal anomaly occurs during the formation of the egg or sperm and is not related to factors like inheritance or obstetric difficulties during birth. The additional genetic material disrupts normal development, leading to the characteristic features associated with Down syndrome. Options 1, 2, and 3 are not accurate explanations for the cause of Down syndrome. It is crucial to understand that Down syndrome is a chromosomal disorder and is primarily determined by the presence of an extra chromosome rather than factors related to brain cell migration, specific genes, or enzyme deficiencies.

Option 4 is the answer, correctly identifying the presence of an extra twenty-first chromosome as the cause of Down syndrome.