Risk assessment

The evaluation of scientific information on the hazardous properties of environmental agents and on the extent of human exposure to those agents. The product of the evaluation is a statement regarding the probability that populations (expressed qualitatively or quantitatively) so exposed will be harmed and to what degree.

Risk characterization

The integration of both qualitative and quantitative information from hazard identification and assessment of exposure and dose-response relationships. It is usually the last step in the risk assessment process and it includes an evaluation of uncertainty and variability in the assessment that would significantly influence the analysis.


Inactivation of a gene by the introduction into cells of double-stranded mRNA for that gene.

Saturation mutagenesis

Mutagenesis screen in which enough mutants are produced to obtain all the different kinds of mutants affecting a particular process.

Selector genes

Genes that encode transcription factors. Transcription factors “select” which other genes will be expressed.

Sensitized strain

A model organism that contains a mutated pathway (e.g., signal transduction pathway), but the mutation causes no visible phenotype. The mutated pathway is close to a threshold of function and sensitive to an otherwise asymptomatic change in activity of a second element in the pathway.

Signal transduction pathway

Type of pathway used for cell-to-cell (intercellular) signaling. Signal transduction pathways can have from 1 to 10 intermediates. These pathways are used extensively during development.

Single nucleotide repeat (SNP)

A variation between individuals in one base pair at a specific location of a DNA sequence.

Spemann organizer

A group of cells that releases inducer proteins that are important in the placement, orientation, and scaling of later development by surrounding cells.

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