geographical barriers features such as rivers or
mountains that prohibit interbreeding by keeping
populations physically separated. (12.2)
germ cell reproductive cell (egg or sperm) produced
through meiosis. (Appendix 4)
germ cell mutation permanent change in genetic
material in a reproductive cell of an organism.
(9.1)
germ-line therapy gene therapy that alters the
genetic information contained in egg and sperm
cells. In theory, this kind of therapy could
eliminate inherited genetic disorders. Research
into this kind of therapy is currently banned in
Canada and in many other countries. (9.4)
gigantism excess of HGH during childhood causes
elongation of the long bones, resulting in a very
tall stature. This excess is often caused by a
tumour in the pituitary gland. (6.1)
glaucoma build-up of the aqueous humour in the
eye that irreversibly damages the nerve fibres
responsible for peripheral vision. (5.3)
global warming rise in average temperatures on
Earth. (15.3)
glomerular filtration the movement of water, salts,
nutrients, and waste molecules from the blood to
the kidney. (4.2)
glomerulus the blood vessel inside the Bowman’s
capsule, from which the water, salts, nutrient
molecules, and waste molecules leave the blood
to be filtered by the kidney. (4.2)
glucagon hormone produced in the islets of
Langerhans in the pancreas that raises blood
glucose by stimulating the breakdown of
glycogen. (4.3)
glutamate neurotransmitter in the cerebral cortex
that accounts for 75 percent of all excitatory
transmissions in the brain. (5.2)
glycolysis metabolic pathway in which glucose
molecules are split into pyruvate molecules. (3.1)
goiter swelling of the thyroid gland caused by
insufficient dietary iodine. (6.1)
gradualism the theory that geographical change
occurs through slow but steady processes. (10.2)
Also, in evolution, the theory that change occurs
slowly and steadily within a lineage, before and
after a divergence. Large changes occur by means
of the accumulation of many small changes.
(12.3)
Grave’s disease seehyperthyroidism. (6.1)
greenhouse effect natural phenomenon that traps
heat in the atmosphere near the surface of Earth.
(15.3)
Green Revolution international effort, started in the
1950s, to transfer the farming methods and crop
varieties used successfully in the more developed
countries to less developed nations. (15.2)
growth factors protein molecules that prolong the
effects of HGH on bone and cartilage tissues. (6.1)
growth rate (r) the number of births minus the
number of deaths over a given period of time.
(14.2)
guanine (G) one of four nitrogen-containing bases in
a nucleotide that make up DNA and RNA. Its
name derives from the fact that it occurs in high
concentration in the animal excrement guano.
(7.1)habitat place or area with a specific set of abiotic
and biotic characteristics. Organisms have
adaptations to the habitats where they typically
live. (13.1)
Hardy-Weinberg equilibrium condition of a
population in which genotypes of members
maintain the same proportions through several
generations. (11.2)
Hardy-Weinberg principle theory stating that in the
absence of forces that change the proportions of
the alleles at a given locus, the original genotype
proportions will remain constant from one
generation to the next, in a large population with
random mating. (11.2)
helicases set of enzymes that cleave and unravel
short segments of DNA just ahead of the
replicating fork during DNA replication. (7.3)
helper T cell lymphocyte that gives off chemicals
that stimulate other macrophages, B cells, and
other T cells during an immune response. (4.4)
heterozygous describes an individual with two
different alleles at a locus. (11.1)
histamines chemicals that increase the permeability
of blood vessels, causing reddening and swelling
of an area. (4.4)
histone complex of small, very basic polypeptides
that form the core of nucleosomes, around which
DNA is wrapped. (7.2)
homeostasis the body’s maintenance of a relatively
stable internal physiological environment. (4.1)
homologous structures body parts in different
species that have the same evolutionary origin,
but that have different structures and functions
(e.g., wing and arm bones). (10.3)
homozygous describes an individual with two
alleles at one locus that are identical. (11.1)
hormone chemical signal that is sent to many parts
of the body; examples are adrenaline and
noradrenaline from the neurons of the adrenal
gland. (5.2, 6.1)
hormone replacement therapy administration of
low levels of estrogen and/or progesterone to
alleviate the symptoms of menopause. (6.3)H
Glossary • MHR 577