Question

Is DNA always perfectly copied during DNA replication?

Answer 1

In molecular biology, DNA replication is the biological process of making two identical DNA copies from the original DNA molecule. DNA replication occurs in all organisms and functions as the most important part of biological inheritance. This is necessary for the growth of damaged tissue and cell division during repair, and also ensures that each new cell receives its own DNA copy.

Complete answer:
DNA replication is the process of copying a suspicious DNA molecule to produce two identical DNA molecules. Replication is an essential process because each time a cell divides, the two new daughter cells must contain the same genetic information or DNA as the parent cell.
DNA replication is imperfect and errors occur every time ${10^4}$-${10^5}$ nucleotides are added. Genomic integrity is maintained by DNA polymerase proofreading process. DNA polymerase goes one step backwards and removes the mismatched nucleotides via $3'$ →$5'$ exonuclease activity. This process is called proofreading.
The majority of DNA replication errors are generated by mispairings of a different kind: either mispairings between non-tautomeric chemical forms of bases or mispairings between “regular” bases that bond incorrectly due to a minor shift in nucleotide location in space. Wobble is the term for this type of misalignment.
Strand slippage, which occurs during replication mistakes, can result in insertions or deletions of nucleotide bases. A newly synthesized strand can sometimes loop out a little, resulting in the inclusion of an additional nucleotide base. Other times, the template strand loops out a little, causing a nucleotide base to be omitted or deleted from the freshly synthesized, or primer, strand.

Note:
Although DNA replication is a very precise process, errors do happen from time to time, such as when a DNA polymerase inserts the incorrect nucleotide. Uncorrected errors can have catastrophic repercussions, such as cancer, if they are not fixed. Repair processes can correct errors, but in rare circumstances, errors go uncorrected, resulting in mutations; in other cases, repair enzymes are mutated or faulty.