Which one of the following causes a frame- shift mutation?
. Deletion
Substitution of purine for pyrimidine
Substitution of pyrimidine for purine
Transition
Deletion. Point mutations that are frame-shift mutations put the normal reading frame out of register by one base pair. The inseion 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 base-hydrogen bond locations. Transversions can be caused by defective DNA polymerases.