Transition, in
genetics
Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians, Augustinian ...
and
molecular biology
Molecular biology is a branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, biomolecular synthesis, modification, mechanisms, and interactio ...
, refers to a
point mutation that changes a
purine
Purine is a heterocyclic aromatic organic compound that consists of two rings (pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted puri ...
nucleotide
Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...
to another purine (
A ↔
G), or a
pyrimidine
Pyrimidine (; ) is an aromatic, heterocyclic, organic compound similar to pyridine (). One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has nitrogen atoms at positions 1 and 3 in the ring. The oth ...
nucleotide to another pyrimidine (
C ↔
T). Approximately two out of three
single nucleotide polymorphisms (SNPs) are transitions.
Transitions can be caused by
oxidative deamination and
tautomerization. Although there are twice as many possible
transversions, transitions appear more often in
genome
A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
s, possibly due to the molecular mechanisms that generate them.
Transitions are more likely to be
synonymous substitutions than transversions, as one observes in the
codon table.
5-Methylcytosine is more prone to transition than unmethylated
cytosine
Cytosine () (symbol C or Cyt) is one of the four nucleotide bases found in DNA and RNA, along with adenine, guanine, and thymine ( uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attac ...
, due to spontaneous
deamination
Deamination is the removal of an amino group from a molecule. Enzymes that catalysis, catalyse this reaction are called deaminases.
In the human body, deamination takes place primarily in the liver; however, it can also occur in the kidney. In s ...
. This mechanism is important because it dictates the rarity of
CpG islands.
See also
*
Transversion
References
External links
Diagram at mun.ca
Mutation
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