I
Isoleucine
see amino acids
(I+ C+D) model
Syn. Helmstetter–Cooper Model.
I-like pili See PILI.
Ia antigens
Class II antigens of the murine Major
Histocompatibility Complex.
Ia protein
The Escherichia coli OmpF porin.
IAA
Indole 3-acetic acid
(see auxins).
IAEA
International Atomic Energy Agency.
IAHS
Infection-associated
haemophagocytic syndrome
See: Haemophagocytic Syndrome.
IAP
Intracisternal A-type particle.
Iatrogenic
Refers to any disease or infection which is caused or exacerbated,
unintentionally, as a result of medical intervention – e.g. examination or
treatment.
Ib protein
The Escherichia coli OmpC PORIN.
ibotenic acid
see amatoxins.
IBV
Infectious bronchitis virus (CORONAVIRIDAE).
ICAD
see apoptosis.
ICAM-1
Syn. CD54.
ICAM-2
See CD102.
ICAM-3
See immunoglobulin superfamily.
ICDH
Isocitrate dehydrogenase
see TCA cycle.
ICE
(syn. caspase-1)
see apoptosis.
ice algae
see diatoms.
Ice nucleation bacteria
Those bacteria which, at temperatures just below 0°C, promote
water-to-ice transition by acting as nuclei around which ice crystals can form.
Such bacteria (e.g. strains of Erwinia herbicola, Pseudomonas
fluorescens, P. syringae and Xanthomonas campestris) – whichinclude
some common epiphytes – have been implicated as contributory factors in frost
damage in various agricultural crops. A DNA fragment from P. fluorescens,
when cloned in Escherichia coli, can confer the ice-nucleation
phenotype; the fragment may encode an outer membrane protein of MWt ca. 180000.
When grown at 15°C, most ice-nucleation-positive strains of Erwinia
herbicola shed into the medium vesicles composed of outer membrane; these
vesicles (‘cell-free ice nuclei’) can behave as ice-nucleation centres which are active at −2°C to −10°C.Some
plant tissues survive, without damage, when ‘supercooled’ to several degrees
below 0°C – but may suffer frost damage if ice-nucleation bacteria are present.
Above (approx.) −5°C, the incidence of frost injury can be decreased by
reducing the size of the populations of plant-contaminating ice-nucleation bacteria.
This can be done e.g. by treatment of plant surfaces with antibiotics such as
streptomycin or oxytetracycline; an alternative method is to treat plant
surfaces with non-ice-nucleating bacteria (a form of biological control). A
combination of antibiotic treatment and biological control has been found to
act additively in the control of frost injury in pear trees.
Biologists
who specialize in the study of fish behavior, anatomy, physiology, and
evolution.
imaginal
disk
(i-maj-in-ul)
An island of undifferentiated cells in an insect larva, which are committed (determined) to form a particular organ during metamorphosis to the adult.
An island of undifferentiated cells in an insect larva, which are committed (determined) to form a particular organ during metamorphosis to the adult.
imbibition
[L. imbibere, to
drink in]
The capillary movement of water into germinating seeds and into substances such as wood and gelatin, which swell as a result.
The capillary movement of water into germinating seeds and into substances such as wood and gelatin, which swell as a result.
immune
response
A highly
specific defensive reaction of the body to invasion by a foreign substance or
organism; consists of a primary response in which the invader is recognized as
foreign, or "not-self," and eliminated and a secondary response to
subsequent attacks by the same invader. Mediated by two types of lymphocytes B
cells, which mature in the bone marrow and are responsible for antibody
production, and T cells, which mature in the thymus and are responsible for
cell-mediated immunity.
immunoglobulin
(Ig)
(im-myoo-noh-glob-yoo-lin)
One of the class of proteins comprising the antibodies.
One of the class of proteins comprising the antibodies.
imprinting
A type of
learned behavior with a significant innate component, acquired during a limited
critical period.
inbreeding
The
mating of individuals that are closely related genetically.
inclusive
fitness
The
relative number of an individual's alleles that are passed on from generation
to generation, either as a result of his or her own reproductive success, or
that of related individuals.
incomplete
dominance
A type of
inheritance in which F1 hybrids have an appearance that is
intermediate between the phenotypes of the parental varieties.
incomplete
flower
A flower
lacking sepals, petals, stamens, or carpels.
incomplete
metamorphosis
(met-uh-mor-foh-sis)
A type of development in certain insects, such as grasshoppers, in which the larvae resemble adults but are smaller and have different body proportions. The animal goes through a series of molts, each time looking more like an adult, until it reaches full size.
A type of development in certain insects, such as grasshoppers, in which the larvae resemble adults but are smaller and have different body proportions. The animal goes through a series of molts, each time looking more like an adult, until it reaches full size.
independent
assortment
See Mendel's second law.
independent
variable
In an
experiment, when one factor is manipulated, a second factor responds. The
independent variable is the factor that is manipulated.
indeterminate
cleavage
A type of
embryonic development in deuterostomes, in which each cell produced by early
cleavage divisions retains the capacity to develop into a complete embryo.
indeterminate
growth
A type of
growth characteristic of plants, in which the organism continues to grow as
long as it lives.
induced
fit
The
change in shape of the active site of an enzyme so that it binds more snugly to
the substrate, induced by entry of the substrate.
induction
[L. inducere, to
induce]
(1) The ability of one group of embryonic cells to influence the development of another. (2) In genetics, the phenomenon in which the presence of a substrate (the inducer) initiates transcription and translation of the genes coding for the enzymes required for its metabolism.
(1) The ability of one group of embryonic cells to influence the development of another. (2) In genetics, the phenomenon in which the presence of a substrate (the inducer) initiates transcription and translation of the genes coding for the enzymes required for its metabolism.
inflammatory
response
A line of
defense triggered by penetration of the skin or mucous membranes, in which
small blood vessels in the vicinity of an injury dilate and become leakier,
enhancing the infiltration of leukocytes; may also be widespread in the body.
ingestion
A
heterotrophic mode of nutrition in which other organisms or detritus are eaten
whole or in pieces.
inhibitory
postsynaptic potential (IPSP)
(post-sin-ap-tik)
An electrical charge (hyperpolarization) in the membrane of a postsynaptic neuron caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more difficult for a postsynaptic neuron to generate an action potential.
An electrical charge (hyperpolarization) in the membrane of a postsynaptic neuron caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more difficult for a postsynaptic neuron to generate an action potential.
innate
releasing mechanism
In
ethology, a circuit within an animal's brain that is hypothesized to respond to
a specific stimulus, setting in motion, or "releasing," the sequence
of movements that constitute a fixed action pattern.
inner
cell mass
A cluster
of cells in a mammalian blastocyst that protrudes into one end
of the cavity and subsequently develops into the embryo proper and some of the
extraembryonic membranes.
inositol
trisphosphate (IP3)
(in-nos-i-tahl)
The second messenger, which functions as an intermediate between certain nonsteroid hormones and the third messenger, a rise in cytoplasmic Ca2+ concentration.
The second messenger, which functions as an intermediate between certain nonsteroid hormones and the third messenger, a rise in cytoplasmic Ca2+ concentration.
insertion
A
mutation involving the addition of one or more nucleotide pairs to a gene.
insertion
sequence
The
simplest kind of a transposon, consisting of inserted repeats of DNA flanking a
gene for transposase, the enzyme that catalyzes transposition.
insight
learning
The
ability of an animal to perform a correct or appropriate behavior on the first
attempt in a situation with which it has had no prior experience.
instar
The stage
of an arthropod's life cycle between molts (shedding of the exoskeleton). As an
example, the third instar is the stage of the life cycle between the second and
third molting cycles. Some arthropods molt throughout their entire life and may
have as many as 30 instars. Insects tend to have a set number of instars, the
number varying by species. The instars succeed one another until the final
mature instar, when the organism stops molting.
insulin
A
vertebrate hormone that lowers blood glucose levels by promoting the uptake of
glucose by most body cells and the synthesis and storage of glycogen in the
liver; also stimulates protein and fat synthesis; secreted by endocrine cells
of the pancreas called islets of Langerhans.
interferon
A
chemical messenger of the immune system, produced by virus-infected cells and
capable of helping other cells resist the virus.
interleukin
Interleukin-1,
a chemical regulator (cytokin) secreted by macrophages that have ingested a
pathogen or foreign molecule and have bound with a helper T cell; stimulates T
cells to grow and divide and elevates body temperature. Interleukin-2, secreted
by activated T cells, stimulates helper T cells to proliferate more rapidly.
intermediate
filament
A
component of the cytoskeleton that includes all filaments intermediate in size
between microtubules and microfilaments.
interneuron
An
association neuron; a nerve cell within the central nervous system that forms
synapses with sensory and motor neurons and integrates sensory input and motor
output.
internode
The
segment of a plant stem between the points where leaves are attached.
interphase
The
period in the cell cycle when the cell is not dividing. During interphase,
cellular metabolic activity is high, chromosomes and organelles are duplicated,
and cell size may increase. Interphase accounts for 90% of the time of each
cell cycle.
interstitial
cells
(in-tur-stish-ul)
Cells scattered among the seminiferous tubules of the vertebrate testis that secrete testosterone and other androgens, the male sex hormones.
Cells scattered among the seminiferous tubules of the vertebrate testis that secrete testosterone and other androgens, the male sex hormones.
interstitial
fluid
The
internal environment of vertebrates, consisting of the fluid filling the spaces
between cells.
intertidal
zone
The
shallow zone of the ocean where land meets water.
intrinsic
rate of increase
The
difference between the number of births and the number of deaths, symbolized as
rmax; the maximum population growth rate.
introgression
(in-troh-gres-shun)
The transplantation of genes between species resulting from fertile hybrids mating successfully with one of the parent species.
The transplantation of genes between species resulting from fertile hybrids mating successfully with one of the parent species.
intron
A
noncoding, intervening sequence within a eukaryotic gene.
invagination
[L. in, in
+ vagina, sheath]
The local infolding of a layer of tissue, especially in animal embryos, so as to form a depression or pocket opening to the outside.
The local infolding of a layer of tissue, especially in animal embryos, so as to form a depression or pocket opening to the outside.
inversion
An
aberration in chromosome structure resulting from an error in meiosis or from
mutagens; reattachment in a reverse orientation of a chromosomal fragment to
the chromosome from which the fragment originated.
invertebrate
An animal
without a backbone; invertebrates make up 95% of animal species.
in vitro
fertilization
(vee-troh)
Fertilization of ova in laboratory containers followed by artificial implantation of the early embryo in the mother's uterus.
Fertilization of ova in laboratory containers followed by artificial implantation of the early embryo in the mother's uterus.
ion
(eye-on)
An atom that has gained or lost electrons, thus acquiring a charge.
An atom that has gained or lost electrons, thus acquiring a charge.
ionic
bond
A
chemical bond resulting from the attraction between oppositely charged ions.
isogamy
(eye-sog-uh-mee)
A condition in which male and female gametes are morphologically indistinguishable.
A condition in which male and female gametes are morphologically indistinguishable.
isolating
mechanisms
Mechanisms
that prevent genetic exchange between individuals of different populations or
species; they prevent mating or successful reproduction even when mating
occurs; may be behavioral, anatomical, or physiological.
isomer (eye-sum-ur)
One of several organic compounds with the same molecular formula but different
structures and therefore different properties. The three types are structural
isomers, geometric isomers, and enantiomers.
isomorphic
generations Alternating
generations in which the sporophytes and gametophytes look alike, although they
differ in chromosome number.
isotonic
solution [Gk. isos, equal
+ tonos, tension]
Solutions of equal solute concentration.
isotope (eye-so-tope)
[Gk. isos, equal + topos, place]
One of several atomic forms of an element, each containing a different number
of neutrons and thus differing in atomic mass.
Tags:
immunoglobulin
inhibitory postsynaptic potential
insertion sequence
interferon
interleukin
isotope