Image by NIH-NHGRI.Ī silent mutation is a mutation that results in the change of a codon without a change in the amino acid represented by the codon. In this example, the base A is inserted between T and C. Excision of a transposon from the mutated gene can often restore it to wild type or create a new stable mutant allele. Transposons are found in every living organism studied and are a major driving force in genome evolution. A feature of mutations caused by many plant transposons is that they are unstable. Transposons can cause wide scale chromosome rearrangements and gene mutations. Some transposons copy themselves and multiply in number within a genome. For this discovery, she was awarded the Nobel Prize in Physiology and Medicine in 1983. Transposons were discovered in maize by Barbara McClintock. Image by NIH-NHGRI.Ī common source of inserted DNA is from transposons, sequences of DNA that are able to move from one genomic site and insert into another. When not in multiples of three, insertions and deletions lead to frameshift mutations, altering the amino acid sequence of the protein encoded by the mutated gene.

As described below, insertions and deletions that are in multiples of 3 are referred to as in-frame insertions and deletions and result in the addition or deletion of amino acids from the protein sequence. Their effects on gene function depend on the size of the insertion or deletion, and the location relative to the gene. They can vary in size from one to thousands or more nucleotide bases. Insertions or deletions of DNA are other types of mutations that occur quite frequently. In this example, the base G is substituted for T.

Dna sequence chart