gamete
(Gr. gamos,
marriage). A mature haploid sex cell;
usually, male and female gametes can be
distinguished. An egg or a sperm.
gametic meiosis
Meiosis that occurs during
formation of the gametes, as in humans and
other metazoa.
gametocyte
(Gr. gametes,
spouse, + kytos, hollow vessel). The
mother cell of a gamete, that is, immature
gamete.
ganglion
pl. ganglia (Gr. little
tumor). An aggregation of nerve tissue
containing nerve cells.
ganoid scales
(Gr. ganos,
brightness). Thick, bony, rhombic scales
of some primitive bony fishes; not
overlapping.
gap junction
An area of tiny canals communicating
the cytoplasm between two cells.
gastrodermis
(Gr. gaster,
stomach, + derma, skin). Lining of the
digestive cavity of cnidarians.
gastrolith
(Gr. gaster, stomach, + lithos, stone). Calcareous body in the wall
of the cardiac stomach of crayfish and other
Malacostraca, preceding the molt.
gastrovascular cavity
(Gr. gaster , stomach, + L. vasculum, small vessel). Body cavity in
certain lower invertebrates that functions in
both digestion and circulation and has a
single opening serving as both mouth and
anus.
gastrozooid
(Gr. gaster,
stomach, + zoon, animal). The feeding
polyp of a hydroid, a hydranth.
gastrula
(Gr. gaster, stomach, + L. ula, dim.). Embryonic stage, usually cap or
sac shaped, with walls of two layers of cells
surrounding a cavity (archenteron) with one
opening (blastopore).
gastrulation
(Gr. gaster,
stomach). Process by which an early
metazoan embryo becomes a gastrula,
acquiring first two and then three layers of
cells.
gel
(jel) (from gelatin, from L. gelare, to
freeze). That state of a colloidal system in
which the solid particles form the
continuous phase and the fluid medium the
discontinuous phase.
gemmule
(L. gemma, bud, + ula,
dim.). Asexual, cystlike reproductive unit in
freshwater sponges; formed in summer or
autumn and capable of overwintering.
gene
(Gr. genos, descent). A nucleic acid
sequence (usually DNA) that encodes a
functional polypeptide or RNA sequence.
gene pool
A collection of all of the alleles of
all of the genes in a population.
genetic drift
Random change in allelic
frequencies in a population occurring by
chance. In small populations, genetic
variation at a locus may be lost by chance
fixation of a single allelic variant.
genome
(Gr. genos, offspring, + oma, abstract group). All the DNA in a
haploid set of chromosomes (nuclear
genome), organelle (mitochondrial genome,
chloroplast genome) or virus (viral genome,
which in some viruses consists of RNA
rather than DNA).
genomics
(je-no+miks). Mapping and sequencing
of genomes (= structural genomics).
Functional genomics is development and
application of genome or systemwide
experimental approaches to assess gene
function. Functional genomics uses
information derived from structural genomics.
genotype
(Gr. genos, offspring, + typos, form). The genetic constitution,
expressed and latent, of an organism; the
total set of genes present in the cells of an
organism; contrasts with phenotype.
genus
(je-nus), pl. genera (L. race). A group
of related species with taxonomic rank
between family and species.
germ layer
In the animal embryo, one of
three basic layers (ectoderm, endoderm,
mesoderm) from which the various organs
and tissues arise in the multicellular animal.
germ plasm
Cell lineages giving rise to the
germ cells of a multicellular organism, as
distinct from the somatoplasm.
germovitellarium
(L. germen, a bud, offshoot, + vitellus, yolk).
Closely associated ovary (germarium) and
yolk-producing structure (vitellarium) in
rotifers.
gestation
(L. gestare, to bear).
The period in which offspring are carried in
the uterus.
globulins
(L. globus, a globe,
ball, + -ulus, ending denoting tendency). A
large group of compact proteins with high
molecular weight; includes
immunoglobulins (antibodies).
glochidium
(Gr. glochis, point, + idion, dim.). Bivalved larval stage of
freshwater mussels.
glomerulus
(L. glomus, ball). A
tuft of capillaries projecting into a
renal corpuscle in a kidney. Also, a small spongy mass of tissue in the proboscis
of hemichordates, presumed to have an
excretory function. Also, a concentration of
nerve fibers situated in the olfactory bulb.
gluconeogenesis
(Gr. glykys, sweet, + neos, new, + genesis,
origin). Synthesis of glucose from protein or
lipid precursors.
glycogen
(Gr. glykys, sweet, + genes, produced). A polysaccharide
constituting the principal form in which
carbohydrate is stored in animals; animal
starch.
glycolysis
(Gr. glykys, sweet, + lysis, a loosening). Enzymatic breakdown of
glucose (especially) or glycogen into
phosphate derivatives with release of energy.
gnathobase
(Gr. gnathos, jaw, + base). A median basic process on certain
appendages in some arthropods, usually for
biting or crushing food.
gnathostomes
(Gr. gnathos,
jaw, + stoma, mouth). Vertebrates with
jaws.
Golgi complex
(after Golgi, Italian
histologist). An organelle in cells that serves
as a collecting and packaging center for
secretory products.
gonad
(N.L. gonas, primary sex
organ). An organ that produces gametes
(ovary in the female and testis in the male).
gonangium
(N.L. gonas,
primary sex organ, + angeion, dim. of
vessel). Reproductive zooid of hydroid
colony (Cnidaria).
gonoduct
(Gr. gonos, seed, progeny, + duct). Duct leading from a gonad to
the exterior.
gonopore
(Gr. gonos, seed,
progeny, + poros, an opening). A genital
pore found in many invertebrates.
grade
(L. gradus, step). A level of organismal
complexity or adaptive zone characteristic
of a group of evolutionarily related
organisms.
gradualism
A component
of Darwin’s evolutionary theory postulating
that evolution occurs by the temporal
accumulation of small, incremental changes,
usually across very long periods of
geological time; it opposes claims that
evolution can occur by large, discontinuous
or macromutational changes.
granulocytes
(L. granulus,
small grain, + Gr. kytos, hollow vessel).
White blood cells (neutrophils, eosinophils,
and basophils) bearing “granules” (vacuoles)
in their cytoplasm that stain deeply.
green gland
Excretory gland of certain
Crustacea; the antennal gland.
gregarious
(L. grex, herd). Living in groups or
flocks.
guanine
(Sp. from Quechua, huanu, dung). A white crystalline purine
base, C5H5N5O, occurring in various animal
tissues and in guano and other animal excrements.
guild
(gild) (M.E. gilde, payment, tribute). In
ecology, a group of species that exploit the
same class of environment in a similar way.
gynandromorph
(Gr. gyn,
female, + andr, male, + morphe, form). An
abnormal individual exhibiting characteristics
of both sexes in different parts of the body;
for example the left side of a bilateral
organism may show characteristics of one
sex and the right side those of the other sex.
gynocophoric canal
(Gr. gyne, woman, + pherein, to carry). Groove
in male schistosomes (certain trematodes)
that carries the female.
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