In genetics

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

, an insertion (also called an insertion mutation) is the addition of one or more nucleotide

Nucleotide

Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 base pair

Base pair

In molecular biology and genetics, the linking between two nitrogenous bases on opposite complementary DNA or certain types of RNA strands that are connected via hydrogen bonds is called a base pair...

s into a DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 sequence. This can often happen in microsatellite regions due to the DNA polymerase

DNA polymerase

A DNA polymerase is an enzyme that helps catalyze in the polymerization of deoxyribonucleotides into a DNA strand. DNA polymerases are best known for their feedback role in DNA replication, in which the polymerase "reads" an intact DNA strand as a template and uses it to synthesize the new strand....

 slipping. Insertions can be anywhere in size from one base pair incorrectly inserted into a DNA sequence to a section of one chromosome inserted into another.

On a chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

 level, an insertion refers to the insertion of a larger sequence into a chromosome. This can happen due to unequal crossover

Chromosomal crossover

Chromosomal crossover is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed...

 during meiosis

Meiosis

Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....

.

N region addition is the addition of non-coded nucleotides during recombination

Genetic recombination

Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method...

 by terminal deoxynucleotidyl transferase

Terminal Deoxynucleotidyl Transferase

Terminal deoxynucleotidyl transferase , also known as DNA nucleotidylexotransferase or terminal transferase, is a specialized DNA polymerase expressed in immature, pre-B, pre-T lymphoid cells, and acute lymphoblastic leukemia/lymphoma cells...

.

P nucleotide insertion is the insertion of palindromic sequences

Palindromic sequence

A palindromic sequence is a nucleic acid sequence that is the same whether read 5' to 3' on one strand or 5' to 3' on the complementary strand with which it forms a double helix....

 encoded by the ends of the recombining gene segments.

Trinucleotide repeats are sometimes classified as insertion mutations and sometimes as a separate class of mutations.

Effects

Insertions can be particularly hazardous if they occur in an exon

Exon

An exon is a nucleic acid sequence that is represented in the mature form of an RNA molecule either after portions of a precursor RNA have been removed by cis-splicing or when two or more precursor RNA molecules have been ligated by trans-splicing. The mature RNA molecule can be a messenger RNA...

, the amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 coding region of a gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

. A frameshift mutation

Frameshift mutation

A frameshift mutation is a genetic mutation caused by indels of a number of nucleotides that is not evenly divisible by three from a DNA sequence...

, an alteration in the normal reading frame

Reading frame

In biology, a reading frame is a way of breaking a sequence of nucleotides in DNA or RNA into three letter codons which can be translated in amino acids. There are 3 possible reading frames in an mRNA strand: each reading frame corresponding to starting at a different alignment...

 of a gene, results if the number of inserted nucleotides is not divisible by three, i.e., the number of nucleotides per codon. Frameshift mutations will alter all the amino acids encoded by the gene following the mutation. Usually, insertions and the subsequent frameshift mutation will cause the active translation

Translation (genetics)

In molecular biology and genetics, translation is the third stage of protein biosynthesis . In translation, messenger RNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or polypeptide, that will later fold into an active protein...

 of the gene to encounter a premature stop codon

Stop codon

In the genetic code, a stop codon is a nucleotide triplet within messenger RNA that signals a termination of translation. Proteins are based on polypeptides, which are unique sequences of amino acids. Most codons in messenger RNA correspond to the addition of an amino acid to a growing polypeptide...

, resulting in an end to translation and the production of a truncated protein. These truncated proteins frequently are unable to function properly or at all and can possibly result in any number of genetic disorders depending on the gene in which the insertion occurs.

In-frame insertions occur when the reading frame is not altered as a result of the insertion; the number of inserted nucleotides is divisible by three. The reading frame remains intact after the insertion and translation will most likely run to completion if the inserted nucleotides do not code for a stop codon. However, because of the inserted nucleotides, the finished protein will contain, depending on the size of the insertion, multiple new amino acids that may affect the function of the protein.

See also

• Indel
  Indel
  Indel is a molecular biology term that has different definitions in different fields:*In evolutionary studies, indel is used to mean an insertion or a deletion and indels simply refers to the mutation class that includes both insertions, deletions, and the combination thereof, including insertion...
  
  
• Loss-of-Function Mutations
• Gain-of-Function Mutations

Further reading

• Pierce, Benjamin A. Genetics: A Conceptual Approach. 3rd ed. New York City: W. H. Freeman and Company, 2008.