The Heritable Disorder Fragile X Syndrome,a Major Cause of Mental

Multiple Choice

The heritable disorder fragile X syndrome,a major cause of mental retardation,is caused by

A) production of enzymes that break the phosphate backbone.
B) UV light.
C) X-rays.
D) presence of an extra X chromosome in the sperm or egg
E) duplication of multiple three-nucleotide repeats.