Final answer:
In DNA, the replacement of a purine with a pyrimidine or vice versa is known as a transversion substitution, which is one of the two main types of point mutations, the other being transition.
Step-by-step explanation:
In DNA, the substitution of a purine for a pyrimidine or a pyrimidine for a purine is called a transversion substitution. This type of mutation occurs when a purine base (adenine or guanine) is replaced by a pyrimidine base (cytosine or thymine), or a pyrimidine is replaced by a purine. Transversion is one of the two types of point mutations, with the other type being a transition, where a purine is replaced with another purine or a pyrimidine is replaced with another pyrimidine.
These point mutations can have various effects on the organism, ranging from benign, such as silent mutations, to more significant changes that can affect protein function. Substitutions, including both transitions and transversions, are the most common nucleotide mutations.