Taq
The bacterium Thermus aquaticus from which a heat stable DNA polymerase used in PCR was isolated.

telomere
A tandemly repeated segment of a short DNA sequences, one strand of which is G-rich and the other strand is C-rich, that form the ends of linear eukaryotic chromosomes.

threshold
The point at which environmental (or genetic) changes produce large phenotypic changes in an organism (or population). For example, there could be a threshold effect of inbreeding on fitness such that after a certain level of inbreeding is reached, individual fitness declines increasingly rapidly.

threshold character
A phenotypic character that contains a few discrete states that are controlled by many genes underlying continuous variation, which affects a character phenotypically only when a certain physiological threshold is exceeded.

Time since the most recent common ancestor
TMRCA.

TMRCA
Time since the most recent common ancestor.

TRAFFIC
A wildlife trade monitoring network sponsored by the WWF and IUCN.

transgressive segregation
Hybridization events that produce progeny that express phenotypic values outside the range of either parental phenotypic value. These differences are usually due to the disruption of polygenic traits.

transition
The more common single nucleotide mutation (or polymorphism) that results from a point mutation in which a purine is substituted with a purine (G↔A) or a pyrimidine is substituted with a pyrimidine (C↔T).

translocation
(1) The movement of individuals from one population (or location) to another that is usually intended to achieve either genetic or demographic rescue of an isolated population. (2) A rearrangement occurring when a piece of one chromosome is broken off and joined to another chromosome.

transposable element
Any genetic unit that can insert into a chromosome, exit, and relocate; includes insertion sequences, transposons, some bacteriophages, and controlling element. A region of the genome, flanked by inverted repeats, a copy of which can be inserted at another place; also called a transposon or a jumping gene.

transposon
A mobile element of DNA that jumps to new genomic locations through a DNA intermediate and which usually carries genes other than those that encode for transposase proteins used to catalyze movement.

transversion
The replacement of a purine with a pyrimidine (A or G to C or T) or vice versa (C or T to A or G). Less common than a transition.

Type I statistical error
The probability of rejecting a true null hypothesis. Usually chosen, by convention, to be 0.05 or 0.01.

Type II statistical error
The probability of accepting a false null hypothesis.