Advocacy in Genetics: A Teaching Guide and Workbook
Glossary of Genetic Terms
Abnormal: A variation from the normal. In the case of genes an abnormal gene may result in a specific disorder.
Acquired mutations: Gene changes that arise within individual cells and accumulate throughout a person’s lifetime; also called somatic mutations.
Age of onset: Age at which the effects of a genotype become evident.
Adenine (A): A base; one of the molecular components of DNA and RNA.
Advanced maternal age: Women over age 34 (age 35 at delivery) are at increased risk for nondisjunction trisomy in the fetus.
AFP (Alpha-fetoprotein): A protein excreted by the fetus into the amniotic fluid and from there into the mother's bloodstream through the placenta.
Alleles: Any one of two or more alternate forms of a gene located at the same locus.
Allelic (gene) frequency: The percentage of alleles (genes) in a population that are of a particular type.
Amino acids: Small molecules that form the building blocks of proteins.
Amniocentesis: Prenatal diagnosis method using cells in the amniotic fluid to determine the number and kind of chromosomes of the fetus and, when indicated, perform biochemical studies.
Amplification: Production of multiple copies of a sequence of DNA.
Anencephaly: One of a series of defects in which the tube of tissue destined to form the brain and spinal cord fails to close, in this case resulting in absence of brain, skull cap, and scalp.
Aneuploidy: State of having a variant chromosome number (too many or too few). (i.e., Down syndrome, Turner syndrome).
Anomaly: Deviation from the average; anything unusual, irregular or contrary to the general rule.
Anticipation: Onset of an inherited disorder at an earlier age, or worsening of symptoms in successive generations.
Artificial insemination: The placement of sperm into a female reproductive tract or the mixing of male and female gametes by other than natural means.
Autosome: Any chromosome that is not part of the pair of sex chromosomes. Humans have twenty-two pairs of autosomes, numbered from 1 to 22.
Autosomal Dominant Trait: Refers to how a disease, condition, or trait is inherited. (Autosomal) the gene involved with the disease is located on a chromosome other than X or Y (sex chromosomes). Therefore the gene will be located on chromosome 1 to 22. (Dominant) all genes occur in pairs. In autosomal dominant conditions, if one of the genes in a pair is not working the disease will be present, it does not matter that the other gene in the pair is functional. Males and females are equally affected. If an individual has a nonfunctional gene, each of his/her children has a 50% chance of inheriting it. Examples of dominant diseases include Huntingtons disease, neurofibromatosis, and most inherited cancers..
Autosomal Recessive Trait: Refers to how a disease, condition, or trait is inherited. (Autosomal) the gene involved with the disease is located on a chromosome other than the X or Y (sex chromosomes). Therefore the gene will be located on chromosome 1 to 22. (Recessive) all genes occur in pairs. In autosomal recessive condition, if one of the genes in a pair is not working, the functional gene is enough to prevent the disease. The condition only occurs when an individual inherits two nonfunctional genes. Men and women are equally affected. If a couple carry the same nonfunctional gene, for each pregnancy, they have a 25% chance of having an affected child, a 50% chance to have a child who is carrier, and a 25% chance to have a child who is not affected and not a carrier. Examples of recessive diseases include cystic fibrosis and sickle cell disease.
Autosome: All chromosomes except those involved in sex determination. Human cells have 22 pairs of autosomes.
Balanced Translocation: Occurs when two chromosomes break and exchange places, leaving the same amount of genetic material. An individual with a balanced translocation will be unaffected, but their children may be affected in a variety of ways.
Bases: The molecular building blocks of DNA and RNA: adenine, cytosine, guanine, thymine, and (in RNA only) uracil. In DNA, A attaches only to T, and C attaches only to G. In RNA, A attaches only to U, and C attaches only to G. Two strands of DNA are held together in the shape of a double helix by weak chemical bonds between their base pairs.
Base pair: Two of the building blocks of DNA held together by weak bonds. In a DNA molecule, adenine always bonds with thymine (A-T), and cytosine always bonds with guanine (C-G).
Base sequence: The order of bases in a DNA molecule.
BRCA1: A gene that normally helps to restrain cell growth.
BRCA1 breast cancer susceptibility gene: A mutated version of BRCA1, which predisposes a person towards developing breast cancer.
Carrier: An individual who carries one copy of a gene mutation for a specific disorder. The carrier is also referred to as a heterozygote. Carriers do not typically develop the disorder, but can pass the gene mutation on to their children. However, only two carrier parents could typically have a child affected with the disorder (see autosomal recessive above).
Carrier Test: A genetic test usually from a blood sample, performed to determine if a healthy individual carries a nonfunctional gene.
Cell: The basic unit of life. All living organisms are a collection of cells.
Centromere: The constricted portion of the chromosome, separating it into its two arms. The region of a chromosome to which spindle traction fibers attach during mitosis and meiosis; where chromatids are held together.
Chorionic villus sampling: An invasive prenatal diagnostic procedure involving removal of villi from the human chorion to obtain chromosomes and cell products for diagnosis of disorders in the human embryo.
Chromatid: The two halves into which a chromosome is longitudinally divided at mitosis and meiosis; one of two strands of DNA held together at the centromere, which exists after a chromosome has made a replica of itself.
Chromatin: The complex of nucleic acids (DNA and RNA) and proteins (histone and nonhistone) of which chromosomes are composed.
Chromosome: A structure of DNA and protein found in the cell nucleus, which carries genes. Normally, each body cell has a total of 46 chromosomes-- 22 paired autosomes and one pair of sex chromosomes (XX=female and XY=male).
Chromosome banding: A technique for staining chromosomes so that bands appear in a unique pattern particular to the chromosome.
Clinodactyly: In-curving of a finger, resulting from angulation at the interphlangeal joints.
Clone: A group of identical genes, cells or organisms derived from a single ancestor. Identical twins are clones, as are colonies of bacteria that reproduce by simple cell division.
Cloning: The process of making genetically identical copies.
Colonoscopy: Examination of the colon through a flexible, lighted instrument called a colonoscope.
Congenital: Present at birth, not necessarily inherited.
Consanguinity: Relationship by descent from at least one common ancestor.
Contiguous genes: Genes physically close on a chromosome that when acting together express a phenotype.
Crossovers: The exchange of genetic material between two paired chromosomes during meiosis.
CYS (Chorionic Villus Sampling): This is a diagnostic procedure sometimes used early in pregnancy (at 9 to 11 weeks of growth) to detect certain genetic disorders.
Cytogenetics: A branch of genetics concerned with the study of chromosomes.
Daughter cells: The two cells which result from division of a single cell.
Deletion: The loss of a segment of the genetic material from a chromosome, which is variable in size and may be detectable at the DNA level (small deletion) or at the chromosomal level (large deletion).
De novo translocation: A chromosomal translocation that appears in an offspring but was not present in either parent.
Derivative chromosome: Chromosome of origin for an abnormal or misplaced piece of chromosomal material.
Differentiation: The complex of changes involved in the progressive diversification in the structure and functioning of the cells during fetal development.
Diploid: Having a full set of genetic material consisting of paired chromosomes that contain one chromosome from each parent.
Direct gene test: A test that can detect specific mutations or alterations in the DNA of a gene.
Disruption: A single event interrupting normal development of an organ leading to structural anomalies. Such disruptions may be of vascular, infectious or even mechanical origin.
Dizygotic: Two cells having been fertilized resulting in twins (fraternal).
DNA (deoxyribonucleic acid): The long, spiraling molecule that orchestrates the cell's daily operations and provides the genetic blueprint for the physical characteristics of all living organisms. Its two strands intertwine like a spiral staircase to form a structure called a double helix. Sub-units, called bases, are the rungs of the staircase and carry the genetic code. (See also RNA).
DNA fingerprinting: A process that uses fragments of DNA to identify the unique genetic makeup of an individual.
DNA repair genes: Certain genes that are part of a DNA repair pathway; when altered, they permit mutations to pile up throughout the DNA.
DNA sequencing: Determining the exact order of the base pairs in a segment of DNA.
Dominant gene (or dominant allele): A gene which, when present, produces a certain trait, and "dominates" over a recessive allele in the gene pair.
Double helix: A common name for DNA; it refers to the molecule's double-stranded spiral staircase structure.
Duplication: Occurs when a chromosome or part of a chromosome is duplicated. This may happen during cell division.
Dysmorphic feature: Developmental abnormality of the form and structure of a certain feature in an individual (often minor structural abnormalities).
Embryo: An organism in the early stages of development (in humans, the developing organism from conception until approximately the end of the second month).
Endonuclease: Restriction enzyme.
Enzyme protein: A type of protein whose function is to act as a catalyst and make chemical reactions possible in living organisms. In the absence of the enzyme, the chemical reaction for which the enzyme is responsible will not take place.
Etiology: Causation; the study of causes, especially of disease.
ELSI: Ethical, legal and social implications (of the Human Genome Project).
Ethics: The study of fundamental principles which defines values and determines moral duty and obligation.
Eugenics: The "improvement" of humanity by altering its genetic composition by encouraging breeding of those presumed to have desirable genes.
Expansion: Addition of multiple copies of trinucleotide repeat sequences during meiosis.
Expressivity: The extent to which a gene’s characteristic is seen in an individual. If a gene is said to have variable expressivity, then the trait may vary from very mild to severe but is never completely unexpressed.
Familial: Characteristic of some or all members of a family.
Familial adenomatous polyposis: An inherited condition in which hundreds of potentially cancerous polyps develop in the colon and rectum.
Familial cancer: Cancer, or a predisposition toward cancer, that runs in families.
Fetoscopy: Method of pre-natal diagnosis where the inside of womb and the developing fetus can be examined visually and sampling can be performed using a fetoscope.
FISH (fluorescence in situ hybridization): A laboratory technique that uses fluorescent tags to identify specific chromosomes or portions of chromosomes.
Fragile sites: A small break or constriction of a chromosome; a non-staining gap of variable width that usually involves both chromatids and is always at exactly the same point on a specific chromosome derived from an individual or kindred.
Functional gene tests: Biochemical assays for a specific protein, which indicates that a specific gene is not merely present but active.
Gamete: A male or female reproductive cell. In the female, an ovum (or egg); in the male, a sperm.
Gene: A defined section of DNA along the chromosome that encodes information for the production of a protein necessary for the functioning of the organism.
Gene amplification: Any process by which specific DNA sequences are replicated disproportionately greater than their representation in the parent molecules; during development, some genes become amplified in specific tissues.
Gene cloning: Isolating a gene and making many copies of it by inserting it into cells and allowing it to multiply.
Gene deletion: The total loss or absence of a gene.
Gene expression: The process by which a gene’s code directs the manufacture of proteins that determine an organism's characteristics (see expressivity).
Gene mapping: Determining the relative positions of genes on a DNA molecule.
Gene markers: Landmarks for a target gene, either detectable traits that are inherited along with the gene, or distinctive segments of DNA.
Gene pair: The two genes, one derived from each parent, with information for producing a protein. One gene comes from the chromosome set contributed by the egg cell; the other gene from the chromosome set contributed by the sperm cell. All genes come in pairs with the exception of genes on the X chromosome in males. Males have only one X chromosome; therefore the genes on the X chromosome in males are present only in a single dose.
Gene therapy: A newly evolving technique designed to treat inherited genetic disorders. The medical procedure involves substituting a healthy gene for an altered gene in the cells of a patient's body.
Gene testing: Examining a sample of blood or other body fluid or tissue for biochemical, chromosomal, or genetic markers that indicate the presence or absence of genetic disease.
Genetic counseling: Education and guidance offered by professional advisors in order to help people make informed decisions based on genetic knowledge. Genetic counseling is intended to help a person understand the meaning of specific information about his or her genes. It also is intended to help a person decide whether to have a genetic test performed or what to do with information provided by such a test.
Genetic engineering: The technology used to genetically manipulate living cells to produce new chemicals or perform new functions.
Genetic linkage map: A chromosome map showing the relative positions of the known genes on the chromosomes of a given species.
Genetic screening: The process of identifying individuals in a population who may be at increased risk for having or being a carrier of a genetic disorder.
Genetic testing: The process of determining whether a person or organism has a certain gene.
Genetics: The scientific study of heredity; how particular traits or qualities are transmitted from parents to offspring.
Genome: All the genetic material in the chromosomes of a particular organism. The human genome consists of three billion bases, organized in about 100,000 genes on a set of chromosomes.
Genotype: The actual genes carried by an individual (see also phenotype).
Germ cells (or germline): Cell line from which gametes are produced.
Germline mutations: (See Hereditary mutation.)
Guanine (G): A base; one of the molecular components of DNA and RNA that forms the genetic code. Always bonds with cytosine (G-C).
Haploid: A single, complete set of chromosomes (half the full set of genetic material), present in the egg and sperm cells of all animals. Human beings have 23 chromosomes in their sex cells. (Compare to diploid).
Hereditary mutation: A gene change in the body’s reproductive cells (egg or sperm) that becomes incorporated in the DNA of every cell in the body; also germline mutations.
Heterogeneity: The production of identical or similar phenotypes by different genetic mechanisms.
Heterozygote: Having two different alleles at a given locus (adjective: heterozygous)
Homologous chromosomes: A "matched pair" of chromosomes, one from each parent, having the same gene loci in the same order.
Homozygote: Having identical rather than different alleles at a given locus. Both alleles have the same mutation. (adjective: homozygous)
Human Genome Project (HGP): A worldwide project aimed at deciphering all the three billion bases of the human genome, including mapping and sequencing every gene. This information will help to more rapidly identify genes causing diseases in humans.
Huntington’s disease: An adult-onset disease characterized by progressive mental and physical deterioration; it is caused by an inherited dominant gene mutation.
Implantation: The attachment of the fertilized ovum to the endometrium or uterine wall, and its embedding in the compact layer of the uterus. This usually occurs at six or seven days after fertilization.
Imprinting: Refers to the phenomenon whereby the effect of inheriting a gene is different depending on whether the inheritance was from the mother or father, e.g., Prader Willi syndrome and Angelman syndrome.
Inborn errors of metabolism: Conditions in which the metabolism of an organism is abnormal because of the presence of one, or a pair of abnormal alleles.
Incomplete penetrance: The gene for a condition is present, but not obviously expressed in all individuals in a family with the gene.
Inversion: Occurs where a chromosome breaks in two and becomes reattached after turning around 180 degrees. Providing no chromosome material is lost, this abnormality should have no effect on the individual. However, that individual may carry the risk of producing eggs or sperm with the incorrect amount of chromosome material.
In vitro: In the test tube or laboratory.
In vivo: Inside a living organism.
Karyotype: A photomicrograph of an individual's chromosomes arranged in a standard format showing the number, size, and shape of each chromosome type.
Late-onset disorder: A disorder, which is not apparent at birth but develops later in the course of an individual’s life.
Leukemia: Cancer that begins in developing blood cells in the bone marrow.
Li-Fraumeni syndrome: A family predisposition to multiple cancers, caused by a mutation in the p53 tumor-suppressor gene.
Linkage analysis of pedigree: The tracking of a gene through a family by following the inheritance of a (closely associated) gene or trait and a DNA marker.
Linkage test: An indirect form of genetic testing in which a known region of DNA located near a gene for a disorder can be used as a "marker" or indicator for that gene. This type of testing is used when the target gene has not yet been identified or when a direct test is not practical because a specific mutation in not known.
Locus: The position that a gene occupies on a chromosome.
Mapping: (See gene mapping, physical map).
Marker: An identifiable physical location on a chromosome that can be identified and followed as it is inherited. This can be a nearby gene which produces a known protein, a restriction enzyme break point, or a series of repeated bases.
Meiosis: The production of sex cells, which are not genetically identical, through a series of cell divisions. Compare to mitosis.
Melanoma: A cancer that begins in skin cells called melanocytes and spreads to internal organs.
Metabolic disorder: A disorder caused typically by an enzyme abnormality in the cells. Usually associated with slower development and growth.
Meiosis: The process of cell division which results in a cell where the 23 pairs of chromosomes split into two, each with 23 chromosomes. These cells are the female ova (eggs) and the male sperm.
Mitochondrial inheritance: The mitochondria are cellular organelles containing DNA, which encode genes that may sustain disease causing mutations. Since only maternal mitochondria are inherited, mitochondrial diseases exhibit non-Mendelian inheritance patterns.
Mitosis: Division of all cells except the reproductive cells with chromosome numbers and genetic make-up identical to that of the parent cell.
Monosomy: The total loss of one of a pair of chromosomes. This occurs, for example, in Turner Syndrome where one X chromosome is lost, leaving a total of 45 chromosomes.
Mosaicism: Where two or more cell populations occur within the body cells, each with a different genetic make-up.
Multifactorial disorder: A disorder brought on by the joint action of multiple factors. The contributing factors include several different genes as well as various types of agents from the environment.
Mutation: A spontaneous or induced change in the DNA of a cell. A gene which has undergone change from the normal gene. This mutation may be an established one or a new sporadic mutation.
Nondisjunction: Failure of two members of a chromosome pair to separate during cell division so that both are passed on to the same daughter cell.
NTD (Neural tube defect): Occurs when there is defective development of the spinal cord and the brain in utero. Conditions such as spina bifida and anencephaly are examples of such developmental defects.
Nucleotide: A molecular subunit of DNA or RNA consisting of a base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule. (See DNA, base pair, RNA).
Nucleus: The portion in the center of each cell which contains the chromosomes with their genetic material.
Oncogenes: Genes that normally play a role in the growth of cells but, when overexpressed or mutated, can foster the growth of cancer.
Ovum: Female egg: reproductive cell carrying 23 chromosomes.
PCR (polymerase chain reaction): A laboratory technique that permits a small DNA section located between two fixed points on the DNA molecule to be duplicated many times, yielding many copies of that DNA section.
Penetrance: An individual who carries a dominant gene may show a variable degree of the symptoms of the disorder.
Phenotype: The observable expression of a gene. Example—brown eye color.
Photomicrography: The technique of making photographs through a light microscope.
Physical map: A map of the locations of identifiable landmarks on DNA, such as genes, or restriction enzyme cutting sites.
Placenta: A complex structure occurring in pregnancy. It is attached to the wall of the womb and connected to the fetus by the umbilical cord. The fetus receives its nourishment through the placenta and the vessels of the umbilical cord.
Precancerous polpys: Growths in the colon that often become cancerous.
Pedictive gene tests: Tests to identify gene abnormalities that may make a person susceptible to certain diseases or disorders.
Predisposition (genetic): The individual concerned is intrinsically more prone to develop a particular disorder.
Presymptomatic test: A genetic test performed to determine if a gene (or genes) is present which will bring on a health problem late in an individual’s life.
Probability: The odds or chance that an event will happen.
Proband: Individual in a family who brought the family to medical attention.
Probe: A specific sequence of single-stranded DNA, typically labeled with a radioactive atom, which is designed to bind to, and thereby single out, a particular segment of DNA.
Prognosis: Prediction of the course and probable outcome of a disease.
Prophylactic surgery: Surgery to remove tissue that is in danger of becoming cancerous, before cancer has the chance to develop. Surgery to remove the breasts of women at high risk of developing breast cancer is known as prophylactic mastectomy.
Proteins: The active molecules in all cells. Proteins control biochemical reactions and determine the physical structure of organisms.
Renal cell cancer: A type of kidney cancer.
Retinoblastoma: An eye cancer caused by the loss of a pair of tumor-suppressor genes; the inherited form typically appears in childhood, since one gene is missing from the time of birth.
Ring formation: Occurs where the ends of a chromosome bend over and fuse together with a loss of genetic material.
Recessive gene (or recessive allele): A gene, which must be present on both chromosomes in a pair to show outward signs of a certain characteristic.
Recombinant DNA: A form of DNA produced by splicing together segments of DNA from two or more organisms.
Restriction enzyme (endonuclease): A protein that breaks the chromosomes apart into many small fragments by cutting the DNA of the chromosomes wherever a specific short sequence of bases occurs. (See also Restriction enzyme cutting site).
Restriction enzyme cutting site: A specific sequence of DNA at which a particular restriction enzyme cuts the DNA.
RFLP (Restriction fragment length polymorphism): Variations occurring within a species in the length of DNA fragments generated by a species endonuclease.
RNA (Ribonucleic acid): A chemical cousin of DNA, RNA is responsible for translating the genetic code of DNA into proteins.
Ribosome: The small cellular structure in which RNA translates the genetic code into proteins.
Robertsonian translocation: Occurs when translocations of chromosomes involve end-to-end fusion with the loss of the short arms. The balanced carrier has 45 chromosomes and is normal; any children may be affected in number of ways.
Screening: Looking for evidence of a particular disease such as cancer in persons with no symptoms of disease.
Selection: The process of determining the relative share allotted individuals of different genotypes in the propagation of a population; the selective effect of a gene can be defined by the probability that carriers of the gene will reproduce.
Sequencing: Determining of the order of bases in a DNA or RNA molecule.
Sex chromosomes: The X and Y-chromosomes in human beings that determine the sex of an individual. Females have two X chromosomes; males have one X and one Y.
Sex determination: The mechanism in a given species by which sex is determined; in many species sex is determined at fertilization by the nature of the sperm that fertilizes the egg.
Single-gene disorder: A disorder which comes about when there is a mutation in a specific gene, and one (for a dominant disorder) or both (for a recessive disorder) of the genes in the gene pair cannot function properly.
Single strand: One half of a DNA double helix.
Somatic cells: Any cell in the body except sex cells.
Somatic mutation: A mutation which occurs in any of the body cells of an individual over the course of that person’s life. Since the mutation is not in the eggs or the sperm cells, it cannot be passed on to children. (See also acquired mutations).
Sonography: Pictures made using echoes from a very high frequency sound.
Sperm: (Abbreviation of spermatozoon) the male reproductive cell carrying 23 chromosomes.
Spina bifida: Open spine, one form of major central nervous system defect.
Susceptibility test: A genetic test for a gene whose presence can increase the chances of developing a health problem later in life. The problem may not develop even if the damaged gene is present, and it may occur even if the gene is absent.
Syndrome: A recognizable pattern or group of multiple signs, symptoms or malformations that characterize a particular condition; syndromes are thought to arise from a common origin and result from more than one developmental error during fetal growth.
Teratogens: Any agent that raises the incidence of congenital malformations.
Thymine (T): A base; one of the molecular components of DNA and RNA. Always bonds with adenine (T-A).
Trait: Any detectable phenotypic property of an organism.
Transcription: The process by which DNA passes genetic information to RNA. Transcription is the first step in producing proteins.
Translation: The process by which RNA makes proteins.
Translocation: The transfer of all or one part of a chromosome to another location on the same chromosome or to a different chromosome after chromosome breakage.
Trinucleotide repeats: Long chains of three bases, e.g., CAG,CAG,CAG,¼and so forth in DNA.
Trisomy: A condition in which there are three, rather than two copies of any one chromosome in the same cell.
Tumor-supressor genes: Genes that normally restrain cell growth but, when missing or inactivated by mutation, allow cells to grow uncontrolled.
Uracil (U): A base; one of the molecular components of RNA. Bonds only with adenine (U-A).
Virus: A noncellular biological entity that can reproduce only within a host.
Wild type: Normal allele or normal phenotype.
X-linked dominant: A pattern of inheritance attributed to genes located on the X chromosome. A disorder will appear when one copy of the nonfunctional gene for that disorder is present. Affected males pass X-linked dominant genes to all their daughters but none of their sons. Affected females pass X-linked dominant genes, on average, to half of their daughters and half of their sons.
X-linked inheritance: This refers to any gene found on the X chromosome or traits determined by such genes; it also refers to a specific mode of inheritance of such genes.
X-linked recessive: A pattern of inheritance attributed to genes located on the X chromosome. Males with the gene will be affected because all the genes on their single X chromosome will be expressed. Females who have two X chromosomes can be carriers. Affected males in a family are related through females.
Zygote: A fertilized egg.
|
