Gene probe
A single-stranded DNA or RNA fragment used in genetic engineering to search for a particular gene or other DNA sequence. The probe has a base sequence complementary to the target sequence and will thus attach to it by basepairing. By labelling the probe, it can be identified after subsequent separation and purification.

Generally Regarded as Safe (GRAS)
Designation given to foods, drugs, and other materials that have been used for a considerable period of time and have a history of not causing illness to humans, even though extensive toxicity testing has not been conducted. More recently, certain host organisms for recombinant DNA experimentation have been given this status.

Gene sequencing
The process of elucidating the nucleotide sequence of a gene. See DNA sequencing.

Gene splicing
A stage in the processing of mRNA, occurring only in eukaryote cells, in which intervening sequences (introns) are removed from the primary RNA transcript (hnRNA), and the coding exons are joined together to form the mature mRNA molecule.

Generation time
See cell generation time.

Gene therapy
Genetic assimilation
Botany: Eventual extinction of a natural species as massive pollen flow occurs from another related species and the natural species becomes more like the related species. Cf gene flow. Genetic code 1. The set of 64 nucleotide triplets (codons) that specify the 20 amino acids and termination codons (VAA, VAG, VGA). 2. The relationships between the nucleotide base-pair triplets of an mRNA molecule and the 20 amino acids that are the building blocks of proteins. See base pair; nucleic acid; nucleotide.

Gene replacement
The incorporation of a transgene into a chromosome at its normal location by homologous recombination, thus replacing the copy of the gene originally present at the locus.