Chromosome abnormality caused by the presence of an additional twenty-first chromosome that results in physical irregularities and mental retardation is
A) cretinism.
B) Down syndrome.
C) phenylketonuria.
D) sickle-cell anemia.

Question

Quizplus · Accepted Answer

Down syndrome is caused by the presence of an extra twenty-first chromosome, resulting in physical abnormalities and intellectual disabilities. Cretinism is caused by a deficiency of thyroid hormones, phenylketonuria is caused by the inability to metabolize the amino acid phenylalanine, and sickle-cell anemia is caused by a mutation affecting the shape of red blood cells. None of these conditions are caused by an extra twenty-first chromosome.

Chromosome Abnormality Caused by the Presence of an Additional Twenty-First