coding segments (EXONs). Functionally, the gene is
defined by the cis-transtest that determines whether
independent MUTATIONs of the same phenotype occur
within a single gene or in several genes involved in the
same function.
See alsoCHROMOSOME.
genealogy The study of one’s family and finding and
recording the complete history of all ancestors within
that family.
gene amplification The selective increase or produc-
tion of multiple copies of a specific gene in an organism
without a proportional increase in others; specific
DNA sequences are replicated disproportionately
greater than their representation in the parent
molecules. For example, a tumor cell amplifies, or
copies, DNA segments naturally as a result of cell sig-
nals or sometimes because of environmental events.
gene cloning Amethod for making identical copies
of a particular DNA; the process of asexually synthesiz-
ing multiple copies of a particular DNA sequence, or
cells (clones), using a bacteria cell or another organism
as a host. The clones are genetically identical to the par-
ent or donor cells. Cloning is used for biomedical
research in the form of extracting stem cells in humans
with the hope of gaining knowledge on the development
of and cure for human diseases. Cloning for producing
children and for medical research is controversial, and
the ethics of such practices are being debated constantly.
gene expression A termdescribing the process of
translating information in DNA into an organism’s
traits. A process by which a gene’s code affects the cell
in which it is found by synthesizing a protein or RNA
product that exerts its effects on the phenotype of the
organism. Expressed genes are transcribed into mRNA
and translated into protein or transcribed into mRNA
but not translated into protein.
gene flow The exchange of genes between different
but usually related populations. Gene flow happens
when an individual or group of individuals migrates
from one population to another, or vice versa, and
interbreeds with its members.
See alsoGENETIC DRIFT.gene pool The total genetic information in all the
genes and combinations in a breeding population at a
given time.generation time The time needed to complete one
generation. A generation spans from a given stage in a
life cycle to the same stage in the offspring.gene therapy A treatment of disease, to correct
genetic disorders, by replacing damaged or abnormal
genes with new normal ones, or by providing new
genetic instructions to help fight disease through the use
of recombinant DNA technology. Therapeutic genes are
transferred into the patient via a weakened virus, a non-
viral vector, or direct delivery of “naked” DNA. Germ
line or heritable gene therapy is used for modification of
reproductive cells. Somatic cell or noninheritable gene
therapy involves those other than reproductive cells.genetic code The language of genetics. The instruc-
tions in a gene that tell the cell how to make a specific
protein. The code defines the series of nucleotides in
DNA, read as triplets called codons, that specifies the
sequence of amino acids in a protein. The set comprises
64 nucleotide triplets (codons) that specify the 20
amino acids and termination codons (UAA, UAG,
UGA).
The code is made up of adenine (A), thymine (T),
guanine (G), and cytosine (C), the nucleotide bases of
DNA. Each gene’s code combines them in various ways
to spell out three-letter triplets (codons) that specify
which amino acid is needed at each step in making a
protein.
See alsoDEOXYRIBONUCLEIC ACID.genetic drift Random changes in allele frequency
over time from one generation to another as the genetic
makeup of a population drifts at random over time140 genealogy