Which of the following could explain how some (although rare) people can have Down syndrome and have a normal chromosome number?

A. One of the cells during development had
trisomy 21 but then died.
B. A large enough fragment of chromosome
number 21 underwent a duplication event.
C. A large enough fragment of chromosome
number 21 underwent a deletion.
D. Some of the genes in one chromosome
number 21 are mutated.
E. None of the answer options explains this
observation.


B

Biology & Microbiology

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