Editing Point mutation (section)

===Transition/transversion categorization===
[[File:TsTvMutation.jpg|thumb|300px|[[Transition (genetics)|Transition]]s (Alpha) and transversions (Beta).]]
In 1959 [[Ernst Freese]] coined the terms "transitions" or "transversions" to categorize different types of point mutations.<ref>{{cite journal |author=Freese, Ernst |title=The difference between spontaneous and base-analogue induced mutations of phage T4 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=45 |issue=4 |pages=622–33 |date=April 1959 |pmid=16590424 |pmc=222607 |doi=10.1073/pnas.45.4.622|bibcode=1959PNAS...45..622F |doi-access=free }}</ref><ref>{{cite journal | author=Freese, Ernst | title=The Specific Mutagenic Effect of Base Analogues on Phage T4 | journal=J. Mol. Biol. | year=1959 | pages=87–105 | volume=1 | doi=10.1016/S0022-2836(59)80038-3 | issue=2 }}</ref> Transitions are replacement of a [[purine]] base with another [[purine]] or replacement of a [[pyrimidine]] with another pyrimidine. Transversions are replacement of a purine with a pyrimidine or vice versa. There is a systematic difference in mutation rates for [[transition (genetics)|transition]]s (Alpha) and [[transversion]]s (Beta).  Transition mutations are about ten times more common than transversions.