Phenotype. An organism’s observable characteristics or traits, such as coloration, size, or the presence or absence of disease. A phenotypic trait may be influenced by genes (genotype), the environment, or both. (http://www.genome.gov/glossary/index.cfm?id=152)

Phenotyping. Diagnostic testing in order to infer the genotype (see above) of an individual based on his or her phenotype (see above). (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=glossary#IX-T)

Phosphorylation. The attachment of a phosphate group to a protein by an enzyme known as a kinase (see above). Posttranslational phosphorylation, one of the most common protein modifications that occurs in animal cells, often serves to regulate the protein’s biological activity (see also Posttranslational modification). (http://themedicalbiochemistrypage.org/protein-modi-fications.html# phosphorylation)

Placebo. “An inactive substance or treatment that looks the same as, and is given the same way as, an active drug or treatment being tested. The effects of the active drug or treatment are compared to the effects of the placebo.” (http://www.cancer.gov/dictionary/?CdrID=46688)

Placebo concurrent control. In a clinical trial, the “test drug is compared with an inactive preparation designed to resemble the test drug as far as possible.” (21 CFR 314.126)

Pluripotent stem cell. “A cell that is able to develop into many different types of cells or tissues in the body” (see also Stem cell, Differentiation). (http://www.cancer.gov/dictionary/?CdrID=44797)

Polymorphism. Variations in the sequence of a particular gene. The most common of these involve differences in one nucleotide among the thousands that can comprise a gene; these are known as single-nucleotide polymorphisms (see below). Some polymorphisms involve long stretches of DNA that differ between versions of the same gene. (http://www.genome.gov/glossary/index.cfm?id=160)

Postmarket. Evaluations, activities, and decisions that occur after regulatory approval, clearance, or registration of a medical product for marketing.

Posttranslational modification. Enzyme-mediated alterations of newly translated proteins, such as the addition of chemical groups including acetyl (see Acetylation), carbohydrates (see Glycosylation), methyl (see Methylation), or phosphate (see Phosphorylation). (http://walsh.med.harvard.edu/pubs/PDFs_2/PTM_review.pdf)

Preclinical studies. Investigations of toxicity, pharmacological activity, and other characteristics of a promising drug candidate that occurs prior to research with human participants.