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Discussion Starter · #1 ·
A 6-year-old boy is brought to the physician by his parents because of mild mental retardation. The parents state that their two other school-aged children also have a similar condition. Laboratory studies show a specific chromosomal breakage site in metaphase studies of lymphocytes cultured with methotrexate. Which of the following chromosomes is most likely to be specifically affected?
A. X
B. Y
C. 13
D. 18
E. 21

Source: Kaplan Q bank
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