Transition (genetics)

Transition (genetics)

In genetics, a transition is a type of point mutation that changes a purine nucleotide to another purine (A ↔ G) or a pyrimidine nucleotide to another pyrimidine (C ↔ T). This is in contrast to a transversion, which involves a purine being swapped for a pyrimidine, or vice versa.

Mechanism

Transitions occur due to the tautomeric shift of the bases, which can lead to mispairing during DNA replication. For example, the amino form of adenine can shift to its imino form, which pairs with cytosine instead of thymine. Similarly, the keto form of guanine can shift to its enol form, pairing with thymine instead of cytosine.

Consequences

Transitions can have various effects on the genome depending on their location:

• In coding regions, they may result in synonymous mutations, which do not change the amino acid sequence of the protein, or nonsynonymous mutations, which do.
• In non-coding regions, transitions can affect gene regulation by altering promoter or enhancer sequences.

Detection

Transitions can be detected using various molecular biology techniques, such as DNA sequencing, polymerase chain reaction (PCR), and restriction fragment length polymorphism (RFLP) analysis.

Examples

• The sickle cell anemia mutation is a well-known example of a transversion, not a transition.
• The lactase persistence mutation in humans is an example of a transition.

See also

• Transversion
• Point mutation
• DNA replication
• Mutagenesis