DNA replication is the process leading to the creation of two copies of DNA from one copy.
Semi-conservative replication limits the number of mutations (in this case, replication errors) resulting from the replication process.
This is achieved by separating the two strands of the parent DNA and then assembling complementary strands for each of them.
As a result, the new DNA molecules each consist of one old and one new strand (hence the name semi-conservative).
Having one parent strand act as a template minimises the number of errors in the newly synthesised strand.
DNA replication is highly accurate, so entire genes may be identical between two distantly related species.