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Alleles  -  A variation of a gene. Some genes may have several different alleles. For example, the gene for blood type has A, B, and O alleles.
Artificial selection  -  Analogous to natural selection, except that humans control the differential reproductive success of variations within a selected population. See more on Artificial Selection.
Catecholamines  -  Amines that bind to the cell surface and act as hormones or neurotransmitters.
Chemoreception  -  The neurological process of receiving information from a chemical signal.
Configurational key stimuli  -  A key stimulus (KS) composed of multiple stimuli that together produce a response.
Conspecifics  -  Members of the same species.
Dizygotic twins  -  Twins born from the simultaneous fertilization of two different eggs by two different sperm.
Endocrinology  -  The study of the bodily secretions, namely hormones, that affect the organism in which they are produced.
Exteroreceptors  -  Neurological receptors that receive information from the environment external to the organism.
Feedback systems  -  Any system that modifies operation based on the abundance or effects of its products.
Fixed action pattern (FAP)  -  A complex behavioral sequence that is indivisible and runs to completion. FAPs are invariant and are produced by the innate releasing mechanism (IRM) that responds to a key stimulus (KS).
Ganglion  -  Bundles of nerves, often found in invertebrates lacking a true brain.
Genes  -  Specific DNA or RNA sequences that comprise a functional unit.
Genotype  -  The genetic makeup of an individual.
Gonadotropins  -  Steroids that target the reproductive organs.
Heritability  -  The proportion of the total variance in phenotypes that is due to the genetic variance of the trait in question.
Homozygous  -  When the two alleles of a gene on the two sets of chromosomes of an individual are identical.
Hormone  -  Substance produced within the body that produces a specific effect in its target organ.
Hypothalamus  -  A region of the brain that collects and funnels information into the pituitary gland.
Innate releasing mechanism (IRM)  -  The mechanism by which an organism responds to a key stimulus (KS) with a fixed action pattern (FAP).
Interactive FAP sequences  -  Chains of behavior where one fixed action pattern (FAP) acts as a key stimulus.
Interoreceptors  -  Neurological receptors that receive information about the organism's internal body.
Key stimuli  -  The stimulus that releases a fixed action pattern (FAP).
Lateral inhibition  -  A system of vision in which excited neurons inhibit neighboring neurons to make edges appear sharper.
Mechanoreceptors  -  Neurological receptors that receive tactile information through deformation of the neuron.
Monozygotic twins  -  Twins resulting from the division of a fertilized egg.
Natural selection  -  The mechanism by which evolution produces population changes through the differential survival and reproduction of members of a population.
Neurons  -  Nerve cells.
Neurosecretions  -  Analogous to hormones, but produced by specialized neurons and carried through the axons.
Neurotransmitter  -  Chemicals released by the axon terminals of one neuron to stimulate another neuron when it is picked up by its dendrites.
Oxytocin  -  A peptide hormone that stimulates uterine contractions and milk secretion.
Peptides  -  Chains of amino acids. In endocrinology, peptide refers to short-chain hormones and neurotransmitters that bind to the cell surface.
Phenotypic  -  The expressed characteristics of an individual.
Pheromones  -  A chemical secreted by an organism that affects conspecifics.
Photoreceptors  -  Neurological receptors that receive visual information.
Pituitary gland  -  The master endocrine gland located in the brain that controls the entire endocrine system by targeting organs or other glands. The anterior pituitary secretes growth hormones, and stimulates the thyroid and follicles. The posterior pituitary stores hormones prior to their release and also produces antidiuretics and oxytocin.
Polygenic inheritance  -  A continuous, rather than discrete, set of traits that are influenced by many genes.
Prolactin  -  A peptide hormone that induces lactation and parental care.
Search images  -  Key stimuli used to find food and other resources.
Steroids  -  17 carbon, 4 ring compounds.
Supernormal releasers  -  Exaggerated stimuli that produce a distorted response.
Thermoreception  -  The process in which the nervous system receives information about temperature.
Tympanic membranes  -  A thin membrane that receives and transmits the vibrations of sound waves to the nervous system for interpretation. Simple ears may consist of only a tympanic membrane, simple receptors, and connective tissue. In more complex ears, the tympanic membrane transmits information to the middle ear.
Vasopressin  -  An antidiuretic that controls the amount of fluid in the body.