Mutations arise from errors in DNA replication or damage from mutagens. They can be point mutations involving a single nucleotide change or larger mutations like deletions, duplications, or inversions. Cells have DNA repair enzymes that minimize mutations by correcting errors during and after replication. However, some mutations evade repair and become permanent if replicated into new daughter DNA. Trinucleotide repeat expansions can cause neurological diseases if the repeats grow too long during replication due to slippage at repeated sequences. Cells deal with DNA damage through bypass, repair, or removal and replacement of damaged sections.