- (B) Down syndrome is caused by an extra chromosome on the twenty-first pair. Klinefelter’s
syndrome results when a boy has an extra X chromosome (XXY). Alzheimer’s and Tay-Sachs are
due to genetic (not chromosomal) abnormalities. Fetal alcohol syndrome is caused by a mother
drinking during her pregnancy.
marvins-underground-k-12
(Marvins-Underground-K-12)
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