Transition

Definition
noun, plural: transitions
(genetics) A small-scale mutation characterized by the replacement of a purine by another purine (e.g. A → G) or a pyrimidine by another pyrimidine (e.g. T → C)
(reproductive biology) The stage of childbirth that occurs before the expulsive phase of labor, and characterized by strong uterine contractions and nearly full cervical dilation
(general) The passing from one state, form, style or place to another
verb
To make or undergo a transition
Supplement
In genetics, transition is a type of mutation. Mutation is defined as a change in the nucleotide sequence of a gene or a chromosome. Based on the effect of mutation on the gene structure, mutations may be: (1) small-scale mutations or (2) large scale mutations. Small-scale mutations are a type of mutation where one or few nucleotides of a gene are affected. They are further classified as follows: (1) substitution mutations, (2) insertion mutations, and (3) deletion mutations. Substitution mutations are a type of mutation in which a nucleotide is substituted with a different nucleotide. Depending on the type of nitrogenous base involved, this type of mutation may be categorized as transition or transversion. A transition is a substitution of a purine nucleotide by another purine (A → G). It may also be a substitution of a pyrimidine by another pyrimidine (C → T). Since transition mutation is associated with only one nucleotide, it may also be a sub-type of point mutation.
In reproductive biology, transition pertains to the stage of childbirth occurring before the expulsive phase of labor, and is characterized by strong uterine contractions and nearly full cervical dilation.
Word origin: Latin transitio (transition)
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