A point mutation, or substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide. Often the term point mutation also includes insertions or deletions of a single base pair (which have more of an adverse effect on the synthesized protein due to nucleotides still being read in triplets, but in different frames- a mutation called a frameshift mutation). For coding sequences one can categorize such point mutations as follows: In biology, mutations are changes to the genetic material (either DNA or RNA). ... An illustration of an insertion at chromosome level At DNA level, an insertion means the insertion of a few base pairs into a genetic sequence. ... A frameshift mutation (also called a frameshift or a framing error) is a genetic mutation that inserts or deletes a number of nucleotides that is not evenly divisible by three from a DNA sequence. ...

• nonsense mutations: code for a stop, which can truncate the protein.
• missense mutations: code for a different amino acid.
• silent mutations: code for the same amino acid.

For example, sickle-cell disease is caused by a single point mutation (a missense mutation) in the beta hemoglobin gene that converts a GAG codon into GTG, which encodes the amino acid valine rather than glutamic acid. In genetics, a nonsense mutation is a point mutation in a sequence of DNA that results in a premature stop codon (also called a nonsense codon) in the transcribed mRNA, and possibly a truncated (and often nonfunctional) protein product. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Missense mutations or nonsynonymous mutations are types of point mutations where a nucleotide is changed which results in a different amino acid. ... Silent mutations or synonymous mutations are DNA mutations that, although they alter a particular codon, they do not alter the final amino acid, and hence do not affect the final protein. ... Phenylalanine is one of the standard amino acids. ... Sickle-cell disease is a general term for a group of genetic disorders caused by sickle hemoglobin (Hgb S or Hb S). ... 3-dimensional structure of hemoglobin. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... RNA codons. ... Phenylalanine is one of the standard amino acids. ... Valine is one of the 20 natural amino acids, and is coded for in DNA. Nutritionally, valine is also an essential amino acid. ... Glutamic acid (Glu), also referred to as glutamate (the anion), is one of the 20 proteinogenic amino acids. ...

Point mutations that occur in non-coding sequences are most often without consequences, although there are exceptions. If the mutated base pair is in the promoter sequence of a gene, then the expression of the gene may change. Also, if the mutation occurs in the splicing seat of an intron, then this may interfere with correct splicing of the transcribed pre-mRNA. In genetics, a promoter is a DNA sequence that enables a gene to be transcribed. ... Diagram of the location of introns and exons within a gene. ... Pre-mRNA (preliminary mRNA) is a single strand of ribonucleic acid (RNA), synthesized from the DNA in the nucleus of a cell by the process transcription. ...

Causes

Point mutations may arise from spontaneous mutations that occur during DNA replication. The rate of mutation may be increased by mutagens. Mutagens can be physical, such as radiation from UV rays or X rays, or chemical (molecules that misplace base pairs or disrupt the helical shape of DNA). Mutagens associated with cancers are often studied to learn about cancer and its prevention. In biology, mutations are changes to the genetic material (either DNA or RNA). ... This article or section is in need of attention from an expert on the subject. ... In biology, a mutagen (Latin, literally origin of change) is a physical or chemical agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. ... Note: Ultraviolet is also the name of a 1998 UK television miniseries about vampires. ... An X-ray picture (radiograph), taken by Wilhelm Röntgen, of Albert von Köllikers hand. ...