G-10 glossary
gene pool Sum total of all genotypes in a population. More
accurately, allele pool.
gene therapy Generally, the transfer of one or more normal
genes into body cells in order to correct a genetic defect.
genetic abnormality An uncommon version of an inherited
trait.
genetic code [After L. genesis, to be born] The correspon-
dence between nucleotide triplets in DNA (then in mRNA)
and specific sequences of amino acids in the resulting poly-
peptide chains; the basic language of protein synthesis.
genetic disorder An inherited condition that results in mild
to severe medical problems.
genetic drift A microevolutionary process; a change in allele
frequencies over the generations due to chance events alone.
genetic engineering Altering the information content of
DNA through use of recombinant DNA technology.
genetic recombination Presence of a new combination of
alleles in a DNA molecule compared to the parental geno-
type; the result of processes such as crossing over at meiosis,
chromosome rearrangements, gene mutation, and recombi-
nant DNA technology.
genome All the DNA in a haploid number of chromosomes
of a species.
genomics The study of whole genomes.
genotype (jeen-oh-type) Genetic constitution of an indi-
vidual. Can mean a single gene pair or the sum total of the
individual’s genes. Compare phenotype.
genus (jeen-us, jen-er-ah), plural: genera [L. genus, race,
origin] A grouping of species more closely related to one
another in body form, ecology, and history than to others at
the same level of classification.
germ cell The cell of sexual reproduction; germ cells give
rise to gametes. Compare somatic cell.
germ layer One of three primary tissue layers that forms
during gastrulation and that gives rise to certain tissues of the
adult body. Compare ectoderm; endoderm; mesoderm.
gland A secretory cell or multicellular structure derived from
epithelium and often connected to it.
glial cells Any of the large number of cells in the nervous
system that support neurons physically or in other ways.
global climate change Major shifts in weather patterns
worldwide.
global warming A long-term increase in the temperature of
Earth’s lower atmosphere.
glomerulus (glow-mare-you-luss), plural: glomeruli [L. glo-
mus, ball] The first portion of the nephron, where water and
solutes are filtered from blood.
glucocorticoid Hormone secreted by the adrenal cortex that
influences metabolic reactions that help maintain the blood
glucose level.
gluconeogenesis The process by which liver cells synthesize
glucose.fossil fuels The fossilized remains of ancient forests.
Examples include oil, coal, and natural gas. Fossil fuels are
nonrenewable resources.
fovea Funnel-shaped depression in the center of the retina
where photoreceptors are densely arrayed and visual acuity
is the greatest.
free nerve endings Thinly myelinated or unmyelinated
branched endings of sensory neurons in skin and internal tis-
sues. They serve as mechanoreceptors, thermoreceptors, or
pain receptors.
free radical Any highly reactive molecule or molecule
fragment having an unpaired electron.
FSH Follicle-stimulating hormone. The name comes from
its function in females, in whom FSH helps stimulate follicle
development in ovaries. In males, it acts in the testes as part
of a sequence of events that trigger sperm production.
functional group An atom or group of atoms that is cova-
lently bonded to the carbon backbone of an organic com-
pound and that influences its behavior.
gallbladder Organ of the digestive system that stores bile
secreted from the liver.
gamete (gam-eet) A haploid cell that functions in sexual
reproduction. Sperm and eggs are examples.
ganglia (gang-lee-a), singular: ganglion [Gk. ganglion, a
swelling] Clusters of cell bodies of neurons in regions other
than the brain or spinal cord.
gap junctions Channels that connect the cytoplasm of
adjacent cells and help cells communicate by promoting the
rapid transfer of ions and small molecules between them.
gastric juice Highly acidic mix of water and secretions
from the stomach’s glandular epithelium (HCl, mucus, pep-
sinogens, etc.) that kills ingested microbes and begins food
breakdown.
gastrointestinal (GI) tract The digestive tube, extending
from the mouth to the anus and including the stomach, small
and large intestines, and other specialized regions with roles
in food transport and digestion.
gastrulation (gas-tru-lay-shun) The stage of embryonic
development in which cells become arranged into primary
tissue layers (germ layers); in humans, the layers are an
inner endoderm, an intermediate mesoderm, and a surface
ectoderm.
gene A unit of information about a heritable trait that is
passed on from parents to offspring. Each gene has a specific
location on a chromosome. Chemically, a gene is a sequence
of nucleotides in a DNA molecule.
gene flow A microevolutionary process; a physical move-
ment of alleles out of or into a population as individuals leave
(emigrate) or enter (immigrate); allele frequencies change as
a result.
gene mutation Small-scale change in the nucleotide
sequence of a gene.
gene pair In diploid cells, the two alleles at a given locus on
a pair of homologous chromosomes.
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