Answer:
X: deletion
Y: substitution
Z: insertion
Explanation:
Sometimes when DNA is replicated, the replication machinery makes errors, called mutations. There are a variety of mistakes that can be made.
A deletion, is where at least one base is missed in the sequence, i.,e. the base is removed or deleted from the new sequence
A substitution occurs when one (or more than one) base is replaced with a different base, i.e. the base is substituted out for another one.
An insertion occurs when one or more extra bases are added to the sequence, i.e. they are inserted in.
