Repeats of base triplets?

_____10. Which one of these is caused by repeats of base triplets rather than a whole chromosome?
a) Down syndrome
b) Edward syndrome
c) Klinefelter syndrome
d) fragile-X syndrome
e) Turner syndrome

It is not a) because Down syndrome is caused by nondisjunction, that is, failure for a chromosome to separate from its sister chromatid during meiosis. It is also not b) because Edward syndrome is another example of trisomy. It is not c) because individuals with Klinefelter syndrome have 2 X's and 1 Y. Turner syndrome is when a female is missing an X chromosome. Therefore by elemination we know that d) fragile-x syndrome is the answer.