Which of the following is caused by an abnormal division of the twenty-first chromosome pair?
DSSSB PGT - 2023,
Answer: A
Down syndrome is caused by an abnormal division of the twenty-first chromosome pair, which gives three copies of that chromosome. Turner's syndrome involves a single X chromosome, Klinefelter syndrome involves an extra X in males, and phenylketonuria is a single-gene metabolic disorder. Down syndrome, also called trisomy 21, is the commonest chromosomal cause of intellectual disability, and it becomes more likely as the mother's age rises.
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