Which one of the following causes a frame-shift mutation?
A. TransitionB. Transversion
C. Deletion
D. Substitution of purine for pyrimidine
Answer.
C. Deletion
Point mutations that are frame-shift mutations put the normal
reading frame out of register by one base pair. The insertion of an extra base
pair or the deletion of one or more base pairs falls into this category.
Transitions and transversions are not frame-shift mutations; they are
substitutions of one base pair for another. Substitutions are the most common
type of mutation. In transitions, a purine is replaced by a purine or a
pyrimidine by a pyrimidine. In transversions, a purine is replaced by a
pyrimidine or vice versa. It has been suggested that transitions occur
spontaneously owing to the tautomeric changes in basehydrogen- bond locations.
Transversions can be caused by defective DNA polymerases.
