A point mutation is a type of genetic mutation that occurs when a single nucleotide base is changed, inserted, or deleted from a DNA or RNA sequence of an organisms genome. Point mutations usually occur during DNA replication, which is the process of creating two single strands of DNA from one double-stranded DNA molecule, each of which is a template for the creation of the complementary strand. Point mutations can have a variety of effects on the downstream protein product, including changes in gene expression or alterations in encoded proteins.

There are different types of point mutations, including substitution, insertion, and deletion. Substitution occurs when one base in the sequence is replaced by another base, while insertion occurs when an extra base is added to the sequence, and deletion occurs when a base is deleted from the sequence. Point mutations can also be classified into two types: transition mutations and transversion mutations. Transition mutations occur when a purine base substitutes for another purine base or when a pyrimidine base substitutes for another pyrimidine base, while transversion mutations occur when a purine base substitutes for a pyrimidine base, or vice versa.

Point mutations can arise from spontaneous mutations that occur during DNA replication, or from exposure to mutagens, which are environmental factors that can change an organisms DNA. Mutagens can be physical, such as radiation from UV rays, X-rays, or extreme heat, or chemical, such as molecules that misplace base pairs or disrupt the helical shape of DNA.

Point mutations can have several effects on the behavior and traits of an organism, including beneficial as well as harmful traits or diseases. An advantageous mutation can create an advantage for that organism and lead to the traits being passed down from generation to generation, improving and benefiting the entire population. The scientific theory of evolution is greatly dependent on point mutations in cells.