The correct answer is B. Down syndrome is a genetic disorder caused by an extra copy of chromosome 21. This results in a total of 47 chromosomes instead of the usual 46.
Option A is incorrect because people with Down syndrome have 47 chromosomes, not 46.
Option C is incorrect because people with Down syndrome have 47 chromosomes, not 48.
Option D is incorrect because people with Down syndrome have 47 chromosomes, not 49.
Chromosomes are structures in the nucleus of cells that contain genes. Genes are the basic units of heredity and determine a person’s physical characteristics, such as hair color, eye color, and height.
Down syndrome is a common genetic disorder, affecting about 1 in 700 babies born in the United States. It is more common in older mothers. There is no cure for Down syndrome, but there are many treatments that can help people with the condition live full and productive lives.