Mutation is a sudden change in chromosomal DNA
Mutations can result from a number of events, including unequal crossing–over during meiosis. In addition, some areas of the genome simply seem to be more prone to mutation than others. These "hot spots" are often a result of the DNA sequence itself being more accessible to mutagens (the agent that causes mutation). Mutation is a sudden change in chromosomal DNA or DNA damage, i.e., in a strict sense it covers only those changes which alter the chemical structure of the gene at the molecular level.
DNA replication is for the most part extremely accurate, with an error rate per site of around 10−6 to 10−10 in eukaryotes. However during the process of DNA replication, errors occasionally occur in the polymerization of the second strand (these error rates are generally extremely low, 1 error in every 10−100 million bases). These errors, called mutations, can have an impact on the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. Mutations propagated to the next generation lead to variations within a specie's population.
If a point mutation occurs in a gamete or in a cell that gives rise to gametes, it may be transmitted to offspring and to a succession of future generations. If the mutation has an adverse effect on the phenotype of an organism, the mutant condition is referred to as a genetic disorder/chromosomal abnormality, or hereditary disease. Mutations can also lead to cancer.