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T:

See thymine

Termination codon:

See “Stop codon”

Transition mutation:

A DNA alteration which results in the substitution of one purine of another purine, or one pyrimidine for another pyrimidine.

Trinucleotide repeat:

A sequence of three nucleotides which is repeated. Such regions of the genome may be prone to unstable expansion of the number of repeats with subsequent generations and result in characteristic group of genetic disorders.