Glossary of Terms Relevant to Behavioural Genetics

Adequacy (in the context of science): Refers to the assessment of an explanation or hypothesis. An adequate explanation is stated as clearly as possible, at the appropriate level of simplicity; accounts for most (ideally, all) of the observed regularity; and is consistent with existing scientific knowledge.

Adoption studies: Studies that use the separation of biological and social parentage brought about by adoption to assess the relative importance of genetics and environmental influences. Typically, comparisons are made between adoptees’ resemblance to their biological parents, who did not raise them to their adoptive parents who did. Other studies compare genetically related siblings and genetically unrelated (adoptive) siblings raised in the same family.

Affected: The condition of having a particular trait, usually used in the context of a disadvantageous trait, as for a disease symptom.

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

Aggression: Behaviour 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.

Animal selection studies: A tool for detecting genetic influences on behavior. A quantitative trait is measured in animals of mixed genetic background, which produces a continuous distribution of phenotypes. Animals exhibiting high and low extremes for the trait are selected as parents for the next generation. If the trait has a genetic basis, then there will be divergence over time in the value of the trait in offspring selected for high and low values.

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

Association studies: An approach used to test whether a gene influences a trait. Comparisons are made between observations of alleles for a candidate gene in populations of individuals with or without the trait. If a particular allele is observed more often in the group with the trait than in the group without the trait, then that allele may influence the trait.

Attention deficit hyperactivity disorder (ADHD): A behavioral disorder that appears to be influenced by genetics. It is characterized by problems with maintaining attention and by impulsivity and hyperactivity.

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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 behaviour 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 behavioural.

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).

Behaviour: 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 behaviour.

Behavioural genetics: The study of the relationship between genetics and environment in determining individual differences of behaviour.

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.

Brain plasticity: A characteristic of neoteny, which describes variations in brain development due to chance that can contribute to differences in behavior.

Candidate gene: A gene that is postulated to influence a trait based on one or more lines of evidence such as linkage, association and mutational analysis, or biochemical considerations.

Chiasma (plural is chiasmata): The point of crossing over during prophase I of meiosis in which there is an actual exchange of genetic material between the paired maternal and paternal copies of chromosomes.

Chi-square: A statistical test that evaluates how well a set of observations fit a predicted outcome. The chi-square is often referred to as a “goodness-of-fit” test.

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.

Coding region: A stretch of DNA sequence (in a gene) that encodes protein.

Codominance: The condition in which a pair of alleles for a given locus contributes equally to the phenotype of the heterozygote who bears them.

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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 behaviour and therefore lead to such a complexity in determining the ‘cause’. See also 'Nature v. nurture'.

Concordance: The presence of a particular trait in two or more family members, such as twins.

Congenital: Existing from birth (note that this term does not distinguish whether the condition is inherited, environmental, or both).

Continuous variation: A type of phenotypic variation that displays a wide distribution of phenotypes in a population due to the interaction of many genes (polygenic causation) or to genetic and environmental factors (multifactorial causation).

Correlation: A statistic that describes the magnitude and direction of association between two measurements or observations. A correlation of 1.0 means that knowledge of one observation reliably predicts the second observation; a correlation of -1.0 means that the two observations are associated in the opposite direction; and a correlation of 0 means that the two observations are unrelated.

Credible (in the context of scientific methods): The condition of being reliable and based on acceptable methods, as in reference to evidence that meets scientific criteria for accuracy and reproducibility.

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

Cytogenetics: A subdiscipline of genetics that combines the study of the cell with the study of genetics, often focusing on the structure, function, and behavior of chromosomes.

Deletion (in the context of molecular genetics): The absence of one or more nucleotides normally found in a gene, resulting in a mutation.

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

Determinism: A concept from philosophy that maintains that all human thought and action is completely determined by physical and biological forces. A consequence of determinism is that freedom and autonomy cease to exist.

Developmental autonomy (in the context of ethics): Having sufficient mental and emotional maturity to be capable of informed consent.

Diploid: Having two copies of each chromosome; a diploid cell has a chromosome number of 2n. In humans, the diploid number is 46.

Discrete variation: Refers to a type of phenotypic variation that displays a small number of distinct phenotypes typically due to the actions of a single or a few genes (for example, Huntington disease; blood groups).

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Dizygotic (DZ) twins: Twins formed from separate fertilized eggs. Fraternal twins share 50 percent of their genes, on average, as with any other sibling.

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).

Dualism: A view of human nature derived from René Descartes’ philosophy that maintains that mind and body are separate.

Dyslexia: A specific reading disability that is influenced by genetics.

ELSI: Ethical, Legal, and Social Implications, a division of the Human Genome Project.

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: meaning “well born”; an application of human genetics initiated by Francis Galton (1822–1911), Charles Darwin’s half-cousin. Eugenics sought to improve the human species by encouraging those with desirable characteristics to reproduce while at the same time discouraging those deemed “inferior” from having children.

Eukaryote: An organism in which cells have a membrane-bound nucleus. Eukaryotes have other subcellular organelles, such as mitochondria or, in the case of plant cells, chloroplasts. Humans are eukaryotes.

Gamete: A sexual reproductive cell. Gametes are haploid, having a single (n) complement of genetic material. In humans, the gametes are ova and sperm.

Gel electrophoresis: A laboratory separation technique that uses electricity to move molecules though a molecular sieve made out of a gel-like substance, usually either agarose (natural) or polyacrylamide (synthetic). In biology, the technique is used to sort proteins or nucleic acid molecules by their size.

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.

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. (Not all genes encode

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protein. For example, in the genes for ribosomal RNA, the transcript is the functional product).

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: The human genome is a single haploid set of nuclear chromosomes.

Genotype: The genetic makeup of a cell or organism. Genotype can be contrasted with the phenotype (the detectable attributes). Genotype can also refer to the particular allelic makeup for a given gene.

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).

HD: The abbreviation for the human genetic disorder Huntington disease. HD is a disorder of the nervous system, usually with adult onset of symptoms. It often is used as an example of a single-gene disorder. The disorder is fatal.

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).

Heritable: Capable of being transmitted to offspring.

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

HGP: The Human Genome Project; a large, collaborative, scientific research effort funded in the United States by the U.S. Department of Energy (DOE) and the National Institutes of Health (NIH).

Homolog: One of a pair of chromosomes that contains equivalent genetic information. In germ-line cells, homologs pair with one another during meiosis. One homolog is derived from the mother and one from the father.

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Homozygous: The condition of having identical alleles for a particular gene at a given locus in a chromosome pair.

Hypothesis: A testable idea or explanation proposed in response to previous knowledge and specific observations.

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

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

Informatics: The study of information processing. In the field of biology, informatics generally refers to the study of genetic sequence data.

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 skilfully. Abilities associated with intelligence, such as application of knowledge to manipulate one's environment or thinking abstractly, are often measured by 'objective' criteria (such as tests).

Interactionism: A view of human nature derived from Immanuel Kant’s philosophy that maintains that there is interaction between the physical (brain, nervous system, and body) and the mind.

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.

Karyotype: The entire set of chromosomes of an individual cell made visible by staining and microscopy and (karyogram) arranged by size and chromosome number.

Knockout mouse: A mouse that has both copies of a specific gene inactivated using recombinant-DNA technology.

Linkage analysis: A laboratory procedure that locates a gene of interest by the presence of identifiable markers located close to the gene.

Linked genes: Genes located on the same chromosome. Genes that are close together—tightly linked — are less likely to be separated during recombination.

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

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Marker (in the context of genetics): An identifiable allele that expresses a known phenotype or a molecular tag (such as a DNA or RNA fragment) to signal the presence of an allele or chromosomal location of interest. DNA or RNA fragments also are used to bind to, and thus identify, a particular genetic sequence in a nucleic acid fragment.

Materialism: A view of human nature derived from David Hume’s philosophy that maintains that mind and choice are only manifestations of physical phenomena (brain, nervous system, and body).

Medicalization: The tendency to view undesirable or uncommon behaviors as pathologies that require treatment.

Meiosis: A specialized process of cell division that reduces the chromosome number to the single (haploid) complement (n). Meiosis takes place in germline cells. Meiosis produces four haploid daughter cells from one diploid cell, involving one round of DNA replication.

Mendelian genetics: The fundamental concepts of genetic transmission introduced by Mendel and expanded to include knowledge of genetic linkage and sex chromosomes.

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 behaviour, such as social interactions or planning of future activities.

Mitosis: The process of cell division that ensures that each daughter cell receives an exact copy of the diploid (2n) complement of chromosomes.

Monozygotic (MZ) twins: Twins formed from a single fertilized egg (identical twins). Identical twins share the same genetic endowment.

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

mRNA: Messenger RNA, the fully processed form of the transcript copied from the DNAsequence of a gene and used to direct protein synthesis.

Multifactorial inheritance: Inheritance in which the phenotype results from the combined action of genes and the environment.

Multigenic (Polygenic) 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. If the mutation occurs in the body (somatic cells), the results affect only the individual bearing those cells; if the mutation is in germ-line cells, the change can be transmitted to offspring.

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

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Neoteny: The process in humans (and some other animals) in which stages of growth and development are prolonged well past intrauterine life.

Nondisjunction: Improper separation of homologs or sister chromatids during meiosis or mitosis. During meiosis, this process can result in a diploid condition for a particular chromosome in one gamete and the absence of that chromosome in another gamete.

Nontraditional inheritance: An informal term that refers to new concepts of inheritance that describe processes that were not traditionally understood or taught in Mendelian genetics. For example, imprinting is a process not explained by traditional Mendelian concepts.

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 behaviour a person feels driven to perform. This behaviour can be a physical action (e.g. hand washing) or a mental act (e.g. praying, repeating words silently, counting.) The behaviour is aimed at neutralizing anxiety or distress.

PCR: Polymerase chain reaction. A laboratory technique that exploits DNA polymerases (enzymes that help replicate DNA) derived from bacteria that live at high temperatures. The technique permits the invitro production of large amounts of a specific DNA sequence from a very small amount of sample DNA. The technique is often used to screen for DNA polymorphisms in populations.

Penetrance: The proportion of individuals with a given genotype who express any of the phenotypic features of the trait. Incomplete penetrance refers to the situation in which less than 100 percent of individuals with a given genotype express the associated phenotype.

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.

Phenylketonuria (PKU): A genetic disorder that results from a deficiency of a liver enzyme, phenylalanine hydroxylase. This lack of enzyme activity results in a toxic buildup of phenylalanine metabolites that lead to tissue damage and mental retardation. Newborns diagnosed with PKU can be placed on a special diet, low in phenylalanine, that can prevent the onset of mental retardation.

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

Polymorphic (in relation to DNA): Literally, having more than one form, such as different lengths for a restriction fragment or the presence of two or more genetically distinct types in a population.

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Primer: A short oligonucleotide sequence used to prime enzymatic reactions, such as the polymerase chain reaction (PCR). In the case of PCR, the primer is extended by a polymerase to form a longer DNA strand.

Prokaryote: A colonial or single-celled organism whose cells lack a membrane-bound nucleus. A prokaryote has a relatively simple cell structure without organelles such as mitochondria or chloroplasts. Bacteria are prokaryotes.

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

Public policy: A set of guidelines or rules that results from the actions or lack of actions of governmental entities.

Quantitative trait locus (QTL): One of multiple genes shown to affect a specific trait.

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).

Recessive: A pattern of inheritance in which the phenotypic effects of an allele are masked in hetero zygotes when one of certain other alleles is present. A trait expressed by recessive inheritance is called a recessive trait. A recessive trait is expressed only in homozygotes.

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 fulfilment or failure to fulfil 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 behaviour.

Restriction endonuclease recognition site: A specific DNA sequence that is recognized and cut (digested) by specific members of a class of bacterial enzymes known as restriction enzymes. This process supplies a naturally occurring immune function for bacteria and is exploited in the laboratory to make possible cloning and other molecular techniques involving specifically sized DNA fragments.

Restriction fragment length polymorphisms (RFLPs): the small differences in the length of DNA fragments produced through cutting with restriction enzymes (enzymes that cut DNA at specific sequences). Genetic variation between individuals is reflected in small differences in the length of DNA between the sites recognized by restriction enzymes, thus producing RFLPs. These differences can be exploited to map the location of genes.

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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.

Ribosome: A structure within cells on which protein synthesis occurs. Ribosomes are composed of ribosomal RNA and proteins.

Scatterplot: A graphical representation of correlation data.

Schizophrenia: A mental illness having a genetic component. It is characterized by onset in early adulthood, deterioration in level of function, and psychotic symptoms, such as auditory and visual hallucinations and paranoia.

Short tandem repeats (STRs): A type of DNA polymorphism that is characterized by varying numbers of repeats of a short DNA sequence (usually 2–4 base pairs). STRs are used as markers to help locate new genes and in forensic DNA testing.

Sibling pair analysis: An experimental approach for identifying genes that affect quantitative traits. If pairs of siblings who share two alleles are more alike for a quantitative trait locus (QTL) than pairs of siblings who share one allele, who in turn are more alike than those who share zero alleles, then the QTL is presumed to influence the trait.

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.

Stigmatization (in the context of genetics): A mark of thinking or behavior that assumes that the characteristics of a set or population apply directly to its members. It ignores variability and the individual response to variability. It is an ethical error based on bad science.

Theory (in the context of science): An explanation of a fundamental principle that has been so thoroughly tested and supported by multiple lines of evidence that it is accepted by the scientific community.

Transcription: The process through which an RNA molecule is synthesized by complementary base pairing using DNA as a template. For example, messenger RNA (mRNA) is a product of transcription.

Transgenic mouse: A mouse that has one or more genes added to its genome using recombinant-DNA technology.

Translation: The process of synthesizing a protein molecule. An RNA message (mRNA) directs the order of amino acids being bonded together to form a protein. This process takes place on structures known as ribosomes.

Trinucleotide repeat: A specific sequence of three nucleotides (subunits of DNA) that is repeated, often in large numbers, in a continuous stretch of DNA in particular genes. The mutant gene for Huntington disease, for instance, contains the trinucleotide repeat CAG repeated many times. See short tandem repeats.

Twin studies: An experimental approach that seeks to determine the relative contribution of genetic effects to a trait. It involves comparing the phenotypic similarities between identical

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twins (which share all their genes) with the phenotypic similarities between fraternal twins (which share half their genes, on average).

Validity (in the context of science): The condition of having met scientific criteria, such as being supported by credible evidence, being built on correct premises, and showing sound reasoning.

Variable expressivity: The range of phenotypic effects in individuals with a given genotype. (Note that small differences in the genotype may be pre sent but not obvious.)

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

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

X-linked trait: A pattern of inheritance in which the allele for the trait in question is present on the X chromosome. Males have only one X chromosome, inherited from the mother. For that reason, X-linked traits cannot be passed from father to son.

Zygote: The cell that results from the fusion of a male gamete and a female gamete. A fertilized ovum (egg cell) is a zygote.

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