One disease/disorder caused by a chromosome defect is

One disease/disorder caused by a chromosome defect is

• A. Cystic fibrosis
• B. Sickle cell anemia
• C. Down syndrome
• D. Hemophilia

Answer: (C)

Changes in chromosome number or structure are chromosome defects. Down syndrome is a classic example because it results from having an extra copy of chromosome 21 (trisomy 21). That extra chromosome changes the amount of genetic material in every cell, leading to the developmental differences associated with the condition. Most cases happen when nondisjunction occurs during the formation of eggs or sperm, producing a fertilized egg with three copies of chromosome 21. The other conditions are caused by mutations in specific genes rather than whole chromosomes: cystic fibrosis arises from a mutation in the CFTR gene on chromosome 7, sickle cell anemia from a mutation in the beta-globin gene on chromosome 11, and hemophilia from mutations in genes on the X chromosome. So Down syndrome is the one caused by a chromosome defect.

Changes in chromosome number or structure are chromosome defects. Down syndrome is a classic example because it results from having an extra copy of chromosome 21 (trisomy 21). That extra chromosome changes the amount of genetic material in every cell, leading to the developmental differences associated with the condition. Most cases happen when nondisjunction occurs during the formation of eggs or sperm, producing a fertilized egg with three copies of chromosome 21.

The other conditions are caused by mutations in specific genes rather than whole chromosomes: cystic fibrosis arises from a mutation in the CFTR gene on chromosome 7, sickle cell anemia from a mutation in the beta-globin gene on chromosome 11, and hemophilia from mutations in genes on the X chromosome. So Down syndrome is the one caused by a chromosome defect.