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Alcohol Health Res WorldAlcohol Health Res WorldAlcohol Health and Research World0090-838XNational Institute on Alcohol Abuse and Alcoholism arhw-19-3-182GlossaryGlossary 1995 19 3 182 183 1995Unless otherwise noted in the text, all material appearing in this journal is in the public domain and may be reproduced without permission. Citation of the source is appreciated.
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Adenylyl cyclaseAn enzyme used by cells, including neurons, to relay signals from the exterior to the interior of the cell.

AlleleOne of two or more variants of a gene. Different alleles for a gene serve the same function (e.g., code for a protein that affects a person's eye color) but may result in different phenotypes (e.g., blue eyes or brown eyes).

Amino acidsThe building blocks of proteins. Some amino acids also serve as neurotransmitters.

Antisense oligonucleotideA short string of nucleotides that can bond to messenger RNA (mRNA) and block the process of gene expression.

Association analysisA technique to identify gene variants (i.e., alleles) that might predispose a person to a disease but that are not required for disease development.

Candidate geneA gene that has been implicated in causing or contributing to the development of a particular disease.

Centimorgan (cM)The morgan (M) is the standard unit of measure of the relative distances between genes on a chromosome; for working purposes, the centimorgan (0.01 M) is used.

ChromosomesThreadlike molecules in the cell nucleus that consist of DNA and protein and contain most of the cell's genes. Humans have 46 chromosomes arranged in 23 pairs.

Congenic strainA strain of organisms, such as mice, created by transferring through specific breeding strategies a small segment of a chromosome from one strain into another inbred strain. The only difference between the congenic and the inbred strain is this small chromosome segment.

Crossing overA reaction between the two partners of a chromosome pair during which sections of the chromosomes break off and are exchanged between the partners. Crossing over occurs during meiosis.

Cystic fibrosisA genetic, metabolic disorder affecting primarily the lungs and airways, characterized by the production of thick mucous; it usually is recognized in early childhood and frequently causes death during young adulthood.

CytoplasmThe part of the cell outside the nucleus.

DNAThe abbreviation for deoxyribonucleic acid, the molecule that encodes the genetic information in all organisms except some viruses. DNA molecules usually consist of two strings of nucleotides (see figure). DNA is a component of chromosomes.

DopamineA monoamine neurotransmitter that is important in the parts of the brain that regulate movement, mood, and the rewarding effects of alcohol and other drugs.

ElectrophoresisA technique for separating and purifying molecules of different size according to the relative distance they travel under the influence of an electric current.

EnzymeA protein that catalyzes (i.e., directs and accelerates) chemical reactions in the cell.

GameteAny mature germ cell.

GeneA string of nucleotides that directs the synthesis of a protein.

Gene expressionThe process of converting the genetic information encoded in the DNA into the final gene product (i.e., a protein).

GenomeThe sum of all genes in an organism.

GenotypeThe genetic makeup of an individual organism.

Germ cellA cell responsible for reproduction (i.e., the sperm cells in males and the eggs in females) or its precursors. Germ cells contain only half the number of chromosomes as somatic cells.

HeterozygousHaving different alleles of a gene at corresponding loci on the two partners of a chromosome pair.

HomozygousHaving identical alleles of a gene at corresponding loci on the two partners of a chromosome pair.

Huntington's diseaseA degenerative, genetic disorder of the central nervous system, usually beginning in young to middle age, characterized by progressive mental deterioration and abnormal involuntary muscular movements.

Inbred strainA virtually genetically identical group of organisms derived by inbreeding among a limited number of ancestors. An inbred strain of mice is like a population of identical twins.

Independent assortmentThe principle that during meiosis the two copies of each gene are distributed to the germ cells independently of the distribution of other genes. Independent assortment is limited by the linkage of genes that are located close to each other on the same chromosome and thus tend to be inherited together. (See figure 2, p. 223.)

IsoenzymeAn enzyme performing the same function as another enzyme but having a different amino acid composition. Isoenzymes can differ in their kinetic properties.

Kinetic propertiesThe characteristics of enzymes and other chemicals that describe the speed and effectiveness with which they catalyze a chemical reaction.

Knockout miceMice in which a gene has been deleted or inactivated in both the somatic and the germ cells so that the animals produce no functional gene product.

LinkageThe tendency for genes that are located close to each other on the same chromosome to be inherited together.

Linkage analysisResearch technique to identify gene variants that are necessary or sufficient to cause a disorder (compare with association analysis).

Locus, lociA specific location(s) on a chromosome.

LymphocyteA white blood cell that is important in the body's immune response. Because they contain some proteins also found in neurons, lymphocytes serve as more easily accessible models of some neural functions.

MappingThe process of determining the position of a gene on the chromosome relative to other genes.

MarkerA characteristic by which a cell or molecule can be recognized or identified. Genetic markers consist of specific nucleotide patterns.

MeiosisThe specialized process of cell division that creates germ cells (i.e., sperm cells and eggs). (See figure 2, p. 223.)

Messenger RNA (mRNA)A type of RNA molecule that carries the information copied from a gene and serves as a template for the production of proteins.

MitochondrionAn organelle within a cell that generates most of the cell's energy.

Monoamine neurotransmittersA category of neurotransmitters that transmit signals between neurons. The monoamine neurotransmitters include norepinephrine, dopamine, and serotonin.

Monoamine oxidase (MAO)The enzyme that breaks down monoamine neurotransmitters.

MutationA change, deletion, or rearrangement in the DNA sequence that may lead to the synthesis of an altered protein or to a totally inactive gene incapable of producing a protein.

NeuronA nerve cell.

NeurotransmitterA chemical released by neurons that excites or inhibits other nerve, muscle, or gland cells.

NucleotideThe building block of DNA or RNA. Each nucleotide consists of a sugar component, a phosphate group, and an organic base. Four organic bases exist in DNA (adenine, cytosine, guanine, and thymine) and in RNA (adenine, cytosine, guanine, and uracil). Specific strings of DNA nucleotides make up genes.

OligonucleotideA molecule made up of a small number of nucleotides, typically fewer than 20. Researchers use these in genetic experiments (e.g., to link fragments of DNA together).

OrganelleMicroscopic structures in a cell that have specialized functions (e.g., mitochondria and the nucleus).

PhenotypeThe observable properties, traits, or physical appearance of an organism resulting from the interaction of the genotype with environmental factors.

PlateletA disklike blood cell involved in blood clotting. Because they contain some proteins also found in neurons, platelets frequently serve as more easily accessible models of some neural functions.

Polymerase chain reaction (PCR)An enzymatic technique for producing multiple copies of a specific piece of DNA.

PolymorphismFor a specific gene, the presence of two or more gene variants (i.e., alleles) in a population.

PrimerA molecule that initiates the synthesis of a larger molecule. For example, a short, synthetic piece of DNA serves as a primer to initiate a polymerase chain reaction.

ProbeA piece of DNA used to locate another piece of DNA. The probe, which can bond with the DNA of interest, usually is made radioactive or fluorescent so that it can be detected easily.

ProteinThe product of the genetic information encoded in a gene. Proteins are made up of amino acids whose order is dictated by the gene's nucleotide sequence. Enzymes are one type of protein.

Quantitative traitA trait, or characteristic, that is determined by more than one gene and which exists in many different degrees (i.e., is distributed continuously) within a population. Body height is an example of a quantitative trait.

ReceptorA protein usually found on the surface of a cell that binds to a specific chemical messenger, such as a neurotransmitter.

Recombinant inbred (RI) strainsA set of animal strains derived by inbreeding the offspring from two parent strains. Each strain in an RI set has a unique combination of genes from the parent strains, and all animals in a single strain have the same gene combination. RI strains aid researchers in determining the genes that affect certain traits.

RecombinationThe formation of new combinations and arrangements of genes during meiosis; recombination is achieved by crossing over, independent assortment, and segregation.

Restriction enzymesA group of enzymes isolated from bacteria that cut DNA molecules at specific sites characterized by certain nucleotide sequences.

Restriction fragment length polymorphism (RFLP)A variation among individual organisms in the size and number of DNA fragments generated by the actions of restriction enzymes. These variations can be detected by the differences in the distribution of DNA fragments during electrophoresis.

RNAThe abbreviation for ribonucleic acid, a DNA-like molecule. Different kinds of RNA exist that play specific roles in the process of gene expression.

SegregationThe principle that the two partners of a chromosome pair are separated during meiosis and distributed randomly to the germ cells. Each germ cell has an equal chance of receiving either chromosome.

SequencingThe process of determining the sequence of nucleotides in a piece of DNA or of amino acids in a protein.

SerotoninA monoamine neurotransmitter that affects mood, consummatory behaviors, and the development of tolerance to alcohol.

Somatic cellsAll cells of an organism other than the germ cells.

Transfer RNA (tRNA)A group of RNA molecules that transport specific amino acids to the site of protein synthesis within the cell.

DNA includes four types of nucleotides: adenine, thymine, guanine, and cytosine. Adenine always bonds with thymine, and guanine always bonds with cytosine. These two combinations form the double-stranded DNA molecule.


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