A gene mutation is a change in the sequence of nucleotides that occurs during cell replication (mitosis and meiosis) within a single coding section of DNA. Mistakes can also occur in the transcription of mRNA or the translation of a polypeptide. However, these changes are not considered to be mutations, because they are not permanent changes to the cell. Explain why "mistakes" in transcription or translation are not as serious as mutations in a gene.

The cell has an elaborate mechanism in place that check for and correct the mistakes that happen during replication, transcription or translation. This process is called as proofreading. The incorrect nucleotide added during replication cause the replication to be halted for a while. The DNA polymerase enzyme fixes the error and replication then resumes as normal.

Gene mutation, on the other hand, is a permanent change in the DNA sequence that might lead to cancer.

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