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Behavioral Genetics: Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W Sources

Affective symptoms: When someone has mood or emotional responses that are inappropriate to the behavior and/or stimulus around them.

Aggression: Behavior manifested by destructive and attacking actions, by covert attitudes of hostility and obstructionism, or by a healthy self-expressive drive to mastery. Aggression may arise from innate drives and/or in response to frustration.

Allele: One of two or more alternative forms of a gene; a single allele for each gene is inherited separately from each parent.

Amino Acid: Molecules combined to form proteins. The sequence of amino acids in a protein, and hence protein function, are determined by the genetic code.

Antisocial behavior: Acting in a manner that is hostile or harmful to organized society, especially being or marked by behavior deviating sharply from the social norm.

Attention Deficit Hyperactivity Disorder/Attention Deficit Disorder (ADHD/ADD): A neurobehavioral disorder characterized by an attention span or ability to concentrate that is less than expected for a person’s age. Often there is age-inappropriate hyperactivity, impulsive behavior or lack of inhibition. There are several types of ADHD: a predominantly inattentive subtype, a predominantly hyperactive-impulsive subtype, and a combined subtype. The condition can be cognitive alone or both cognitive and behavioral.

Autosome: A chromosome not involved in sex determination. The diploid human genome consists of 46 chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (the X and Y chromosomes).

Behavior: The response of an individual, group, or species to its environment or within the context of its environment. The term can refer generally to the way in which someone behaves or to an instance of such behavior.

Behavioral genetics: The study of the relationship between genetics and environment in determining individual differences of behavior.

Bipolar disorder or manic depression: A mood disorder characterized by mood swings from mania (exaggerated feeling of well-being) to depression, with a tendency to recur and subside spontaneously. Either the manic or the depressive episodes can predominate and produce mood swings, or the patterns of mood swings may be cyclic. The manic phase is characterized by elation, hyperactivity, over-involvement in activities, inflated self-esteem, a tendency to be easily distracted, and little need for sleep. The manic episodes may last from several days to months. In the depressive phase there is sluggishness (inertia), loss of self-esteem, withdrawal, sadness, and a risk of suicide.

Chromosome: The structure in an organism that contains an individual’s genes. Humans typically have 46 chromosomes in every cell of their body, inheriting half from each parent.If a chromosome is missing, duplicated, or damaged an individual can develop health problems.

Cognitive: Relating to or involving the act or process of knowing, which includes awareness, judgement, perception, reasoning, and conceiving.

Complexity (in genetic and environmental sense): The quality of being hard to separate, analyze, or solve, or being composed of many parts. It is believed that a myriad of both genetic and environmental aspects often contribute to behavior and therefore lead to such a complexity in determining the ’cause.’ See also ‘Nature v. nurture’.

Criminality: The quality or state of engaging in illegal activity.

Deoxyribonucleic acid (DNA): The double-stranded molecule encoding the total genetic information of most organisms.

Diploid: Having a full complement of 46 chromosomes (see haploid).

Dominant trait: Characteristic associated with genes that are reflected in the phenotype both in the homozygous and the heterozygous state (e.g., only one copy of the dominant allele is required to give the characteristic).

Environment: The sum of circumstances, objects, and conditions that surround an individual. The aggregate of social, cultural and physical environmental conditions that influence the life of an individual or community. For the gene, the environment encompasses all conditions external to the gene, including the influence of other genes.

Ethics: The discipline dealing with what is good and bad, and with moral duty and obligation. The term can also refer to a set of moral principles or values, or a theory or system of moral values. Also, the principles of conduct governing an individual or a group.

Ethnicity: Common qualities or affiliation with large groups of people classed according to common racial, national, tribal, religious, linguistic, or cultural origin or background.

Eugenics: The study and application of selective human breeding to achieve a desired set of characteristics.

Gene: The hereditary unit of life in a chromosome. Contains a unique segment of DNA that provides the complete instructions for making a protein or several related proteins that each cell type (e.g., skin, liver) needs to create a unique individual.

Gene pool: The complete set of genetic information in a population; the gene pool includes all alleles present in the population.

Gene therapy: An experimental approach involving the intentional alteration of genetic makeup to affect a phenotypic change. For example, when a ‘normal’ gene is inserted into cells to replace a ‘malfunctioning’ gene that is causing some disease or condition.

Genetic code: Instructions in a gene that tell the cell how to make specific proteins. Each gene’s code combines four nucleotides in various ways to spell “words” that specify which amino acid is needed when making a protein.

Genetic determinism: The view that the development of an organism is determined solely by genetic factors.This view is not supported by scientists.

Genetic screening: The identification or mapping of a person’s genetic structure. During the process, all or part of an individual’s DNA is evaluated to discover whether or not certain genes are present. This mapping can be performed at any stage of life, from ‘pre-implantation’ embryo to adult.

Genetics: The study of the patterns of inheritance of specific traits and their variation among organisms.

Genome: All the genetic material in the chromosome needed to create and maintain an organism.

Genotype: Genetic makeup of a specific gene, a cell, or organism.

Germ line: Cells capable of contributing genetic material to subsequent generations (e.g., eggs and sperm).

Haploid: Cell in which each type of chromosome, for instance a human gamete (e.g., sperm or egg), is present only once, i.e., 23 chromosomes are present (see diploid).

Heredity: The sum of the qualities and potentialities genetically derived from one’s ancestors, or the transmission of such qualities.

Heritability: A term that describes the proportion of phenotypic variation among individuals in a specific population that can be attributed to genetic effects. Heritability is a characteristic of a population, not of an individual, and is an estimate of the relative importance of genetic influences on a trait (as opposed to environmental influences).

Heterozygous: Having two alleles of a gene at a specific locus which are different.

Homozygous: Having two alleles of a gene at a specific locus which are identical.

Identity: The set of behavioral or personal characteristics by which an individual is recognizable as a distinct person (or as a member of a particular group).

Impulsive behavior: An act performed without delay, reflection, voluntary direction or obvious control in response to a stimulus.

Inheritable: A quality that is capable of being transmitted to the next and/or subsequent generations.

Injustice: Wrongful act or omission that denies an individual or group the benefits to which they have a rightful claim, or failure to distribute burdens in a fair manner.

Insanity: A legal term indicating that a person committing a criminal act is unaware that s/he was acting illegally due to a mental disorder.

Intelligence: The ability to learn or understand, to deal with new or trying situations, or to use reason skillfully. Abilities associated with intellegence, such as application of knowledge to manipulate one’s environment or thinking abstractly, are often measured by ‘objective’ criteria (such as tests).

Justice: Fair, equitable, and appropriate treatment in light of what is due or owed to persons. The maintenance or administration of what is just, especially by the impartial adjustment of conflicting claims or the assignment of merited rewards or punishments. The quality of being just, impartial, or fair. The principle or ideal of just dealing or right action, or conformity to this principle or ideal: righteousness.

Locus (plural Loci): The position in a chromosome of a particular gene or allele.

Mental illness: Refers collectively to diagnosable disorders of the brain. Mental disorders are characterized by abnormalities in cognition, emotion or mood, or the highest integrative aspects of behavior, such as social interactions or planning of future activities.

Mood disorders: Emotional behavior inappropriate for one’s age or circumstances, characterized by, for example, unusual excitability, guilt, anxiety, or hostility.

Multigenic traits: Characteristics (phenotypic outcomes) determined by many different genes.

Mutation: The source of genetic variation. A change in the wild type (gene) sequence or in the number or structure of chromosomes that may or may not have observable effect or significant impact on health.

Nature v. nurture: The controversy over whether genetic inheritance (our innate nature) or environment (upbringing) determines behavior. Since both nature and nurture undoubtably contribute to behavior, this ‘either-or’ thinking is not an accepted dichotomy by scientists.

Novelty-seeking: The tendency to seek out and enjoy novel, and sometimes risky, experiences.

Nucleotide: A building block of DNA and RNA.

Obsessive-Compulsive Disorder (OCD): An anxiety disorder characterized by the presence of obsessions or compulsions; having one or both is sufficient for the diagnosis. An obsession is a recurrent or persistent thought that is intrusive or inappropriate. A compulsion is a repetitive behavior a person feels driven to perform. This behavior can be a physical action (e.g. handwashing) or a mental act (e.g. praying, repeating words silently, counting.) The behavior is aimed at neutralizing anxiety or distress.

Phenotype: The visible properties of an organism that are produced by the interaction of the genotype and the environment. The entire physical, biochemical, and physiological makeup of an individual as determined both genetically and environmentally; also, any one or any group of such traits.

Polygenic inheritance: A phenotypic outcome that is determined by more than one gene, such as many physical characteristics or diseases.

Protein: Substances that consist of amino-acid residues joined by peptide bonds. Many essential biological compounds such as enzymes, hormones, or immunoglobulins are proteins.

Race: A classification of people on the basis of their phenotypic characteristics that are presumed to be inheritable. The notion of race as based on specific biological traits is not embraced by most scientists; however, race as a social variable is viewed as a topic meriting scientific investigation.

Recessive trait: Characteristic associated with genes that are reflected in the phenotype only in the homozygous state (e.g., both copies of the recessive allele are necessary to produce the characteristic).

Responsibility: The term has several meanings. To be “causally responsible” is to cause something to happen, either directly or indirectly. To be “legally responsible” is to be held accountable under the law and be subject to legal consequences for one’s actions. To be “morally responsible” is to have a moral obligation, for which the fulfillment or failure to fulfill is deserving of praise or blame. In both morality and law, one’s responsibility is judged in the context of the ability to understand the nature and consequences of one’s actions and to control one’s behavior.

Ribonucleic acid (RNA): A single-stranded nucleic acid that plays a central role in protein synthesis and gene regulation. RNA contains ribose, in contrast to the deoxyribose in DNA.

Somatic cell: Any cell within the body that is not part of the germ line and therefore does not contribute to genetic transmission to future generations.

Violence: Rough, injurious or abusive physical force, action, or treatment, or an instance of such behavior.

Wild type: The naturally-occurring genotype or phenotype for a given organism.



(1) Search under “Find Terms” at the National Library of Medicine’s “Gateway”.
(2) The National Human Genome Project Glossary.
(3) Medical dictionaries and encyclopedias available through NIH’s Medline Plus.
(4) Merriam-Webster’s Online Dictionary.
(5) an online dictionary.
(6) The National Institute of Neurological Disorders and Stroke’s online index of disorders.
(7) Biological Dictionary.
(8) The Oxford Companion to Philosophy.

In Print

(1) Mark V. Bloom et al., “Genes, Environment, and Human Behavior,” (Colorado Springs, CO: Biological Sciences Curriculum Study (BSCS), 2000).
(2) Audrey R. Chapman, “Justice Implications of Inheritable Genetic Modification ” in Audrey R. Chapman and Mark S. Frankel, eds., Designing Our Descendents: The Promises and Perils of Genetic Modification (Baltimore, MD: Johns Hopkins University Press, 2003).
(3) Mark S. Frankel and Audrey R. Chapman, eds., Human Inheritable Genetic Modifications: Assessing Scientific, Ethical, Religious, and Policy Issues ( Washington, DC: American Association for the Advancement of Science, 2000).
(4) Richard Hedges, Bioethics, health care, and the law: a dictionary (Santa Barbara, CA: ABC-CLIO, 1999).
(5) Warren Thomas Reich, ed., Encyclopedia of Bioethics (New York: Macmillan Pub. Co., 1995).
(6) Warren Thomas Reich, ed., The Ethics of Sex and Genetics (New York: Macmillan References USA, 1998).


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