Glossary of Common Terms in Genetics Acquired mutations Gene changes genetic information. DNA is held Multiplexing A sequencing approach that that arise within individual cells and together by weak bonds between base uses several pooled samples simultaneous­ accumulate throughout a person's life pairs of nucleotides: adenine, guanine, ly, greatly increasing sequencing speed. span. cytosine, and thymine. Mutation Any heritable change in DNA Alleles One of a group of genes that Gene The fundamental unit of heredi­ sequence. occur alternatively at a given locus. A ty. A gene is an ordered sequence of single allele is inherited separately from nucleotides located in a particular posi­ Nucleotide A subunit of DNA or RNA each parent (e.g., at a locus for eye tion on a particular chromosome that consisting of a nitrogenous base, a phos­ color, the allele might result in blue or encodes a specific functional product phate molecule, and a sugar molecule. brown eyes). (i.e., a protein or RNA molecule i. Thousands of nucleotides are linked to form a DNA or RNA molecule. Base pair Two nitrogenous bases (ade­ Gene expression The process by which nine and thymine or guanine and cyto- a gene's coded information is converted Oncogene One or more forms of a sine) held together by weak bonds. Two into the structures present and operat­ gene associated with cancer. strands of DNA are held together in the ing in the cell. shape of a double helix by the bonds Polygenic disorders Genetic disorders between base pairs. Gene mapping Determination of the resulting from the combined action of relative positions of genes on a DNA alleles of more than one gene (e.g., Carrier A person who has a recessive molecule and the distance between heart disease, diabetes, and some can­ mutated gene along with its normal them. cers). Although such disorders are in­ allele. Carriers do not usually develop herited, they depend on the simultane disease caused by the mutation, but thev Gene therapy Insertion of normal ous presence of several alleles; thus the can pass the mutated gene on to their DNA directly into cells to correct a hereditary patterns are usually more children. genetic defect. complex than single-gene disorders. Chromosomes The self-replicating Huntington's disease An adult-onset Recombination The process by which genetic structures of cells containing the disease caused by an inherited dominant children derive a combination of genes cellular DNA that bears the linear array gene mutation that is characterized by different from that of either parent. of genes in its nucleotide sequence. progressive mental and physical deterio­ ration. Single-gene disorder Hereditary disor­ Cloning Using specialized DNA tech­ der caused by a mutant allele of a single nology to produce multiple, exact Linkage analysis A gene-hunting tech­ gene (e.g., Duchenne muscular dystro­ copies of a single gene or other segment nique that traces patterns of heredity in phy, retinoblastoma, sickle cell disease). of DNA to obtain enough material for large, high-risk families in an attempt to further study. A second type of cloning locate a disease-causing gene mutation. Tay-Sachs disease An inherited disease exploits the natural process of cell divi­ caused by a recessive gene mutation that sion to make many copies of an entire Locus The position on a chromosome appears in infancy and is characterized cell. A third type of cloning produces of a gene or other marker, or the DNA by profound mental retardation ami complete, genetically identical animals, at that position. early death. such as Dolly the sheep. Marker An identifiable physical loca­ Definitions adapted from Hie Human Genome DNA (deoxyribonucleic acid) A dou­ tion on a chromosome whose inheri­ Project, http://www.ornl.flov/lHinus/publhat/ ble-stranded molecule that encodes tance can be monitored. glossarv.htnil. 80 • MARCH - APRIL 2001 HEALTH PROGRESS JOURNAL OF THE CATHOLIC HEALTH ASSOCIATION OF THE UNITED STATES www.chausa.org HEALTH PROGRESS® Reprinted from Health Progress, March-April 2001 Copyright © 2001 by The Catholic Health Association of the United States.