Gene targeting - the site-specific alteration of a gene through the targeting of DNA sequences to that gene.
Inner cell mass (ICM) - a component of mammalian blastocyst-stage embryos destined to form the embryo proper.
Fibroblast feeder layer - a layer of fibroblasts plated upon which stem cells are cultured that provides both support and nutrients.
Homologous recombination - exchange of genetic material between two identical or near-identical nucleotide sequences.
Hypoxanthine guanine phosphoribosyl transferase (HPRT) - a transferase that plays a central role in the generation of purine nucleotides essential for DNA synthesis. Mutations in HPRT have been shown in humans to result in Lesch-Nyhan syndrome.
Select glossary terms are defined below. For a complete list of glossary terms please refer to the book.