- Mutation is a change in the nucleotide sequence of an organism's genome. There are several types of mutations including substitution, insertion, deletion, and frameshift. - Mutations can be caused by natural DNA replication errors or external mutagens like radiation, chemicals, and viruses. These mutagens can directly damage DNA or produce reactive molecules that cause mutations. - Several genetic disorders in humans are caused by chromosomal mutations, such as Down syndrome from trisomy 21, Edward's syndrome from trisomy 18, and Patau syndrome from trisomy 13. Other disorders involve the loss or gain of whole chromosomes or chromosome segments.