Autosome: All of the 22 pairs of chromosomes that human cells have, excluding the sex chromosomes (X and Y)

B

Base: One of the four nitrogenous substances (adenine, cytosine, guanine, thymine) that are the building blocks of DNA. Different combinations of bases encode different genes and ultimately, proteins.

Base pairs: A complementary building block consisting of a pair of two DNA bases (adenine with thymine, and cytosine with guanine) and represented by one of the rungs within a double stranded DNA molecule.

BRCA1: A gene that when mutated confers a high risk of hereditary breast and ovary cancer.

C

Carrier: person who carries one copy of a disease causing gene, but does not have the actual disease. This person has the potential to pass the disease onto his/her children if the spouse is a carrier as well.

Carrier testing: Genetic testing to identify individuals who carry a disease-causing gene which could be inherited by their children. Carrier testing is designed for healthy people with a family history of a certain disease.

Cell: The basic, membrane bound subunit that makes up the tissues of any living organism.

Chromosomes: The total DNA sequence in the nucleus of each cell is tightly wound to create structures which contain all of your genes; these structures are known as chromosomes. A normal human cell contains 46 chromosomes, of which 22 pairs are autosomes and two are sex chromosomes.

Clone: Identical genes, cells, or organisms derived from the same ancestor.

Cloning: The experimental process of making genetically identical copies

Codominant: Two different alleles of the same gene that are both expressed, for example A and B alleles of the ABO blood group system, or red and white color alleles of a flower resulting in pink coloration.

Codon: A group of three DNA bases along a gene that codes for a single amino acid. All the codons of a gene thus code for the amino acid sequence of its protein.

Crossing over: A phenomenon, also known as recombination, where genetic material is physically exchanged by paired chromosomes mostly during the formation of sperm and egg cells (meiosis).

Cystic fibrosis: An inherited disease in which a thick mucus clogs the glands of the pancreas, lungs, and intestines. The sweat of the affected individual typically has high salt concentrations.

Cytoplasm: The cellular substance external to the nucleus in which all of the cell's components are suspended.

D

DNA (Deoxyribonucleic acid): Known as the substance of heredity, DNA is a large molecule in the shape of a double helix that carries the genetic information for all the proteins a cell needs to survive and replicate.

DNA sequencing: Determining the exact order of the base pairs in a segment of DNA using established scientific techniques.

Dominant allele: A gene that is expressed, regardless of whether its counterpart allele on the other chromosome is dominant or recessive. Autosomal dominant disorders are produced by a single mutated dominant allele, even though its corresponding allele is normal. (See Recessive allele.)

E

Electrophoresis: A technique for separating and analyzing DNA, RNA, or proteins based on physical attributes in an electric field through a gel.

Endonuclease: An enzyme that recognizes and cleaves DNA at specific sequences. Also called restriction enzymes, they are useful to scientists for analyzing gene structure and mutations.

Enhancer: Regulatory genetic elements that interact with genes to increase their expression.

Enzyme: A protein that facilitates a specific chemical reaction.

Euchromatin: Regions of chromosomes that stain lightly under analysis and are thought to contain active, functioning genes.

Exon: The coding portions of genes which are interspersed by non-coding introns. Together, the exons constitute the template from which proteins are made.

F

Familial adenomatous polyposis: An inherited condition in which hundreds of potentially cancerous polyps develop in the colon and rectum.

Familial cancer: A predisposition towards cancer that runs in families.

Familial trait: A trait shared by members of a family.

Frameshift mutation: An alteration of DNA where insertion or deletion of sequence occurs that is not a multiple of three base pairs, thus disrupting the gene/protein’s normal code.

Functional gene tests: Biochemical assays for a specific protein that indicate whether or not that protein is functional.

G

Gene: The fundamental unit of inheritance in the form of DNA. Each of the body's 50,000 to 100,000 genes contains the code for a specific product, typically, a protein such as an enzyme.

Gene deletion: The total loss or absence of a gene.

Gene expression: The process by which a gene's coded information is translated into the structures present and operating in the cell (either proteins or RNAs).

Gene markers: Landmarks along chromosomes that help identify chromosomal locations. Most markers are either detectable traits that are inherited along with a gene in question or distinct segments of DNA.

Gene mapping: The ordering of genes on chromosomes and the approximate distances between them.

Gene testing: The examination of a person’s DNA for biochemical, chromosomal, or genetic markers that indicate the presence or absence of genetic disease.

Gene therapy: The treatment of disease by replacing, manipulating, or supplementing nonfunctional genes.

Genetic engineering: The alteration of genes or their expression.

Genetics: The scientific study of inheritance, and the study of genes through their variation.

Genome: The total DNA from an organism.

Genotype: The gene constitution of an individual (compare to phenotype, which is the observed characteristic into which a gene is translated).

Germ cells: The reproductive cells of the body that mature to become either egg or sperm cells.

Guanine: One of the four DNA bases that encode genes. (Abbreviation: G) Normally pairs with a cytosine base to form a C:G base pair.

H

Haploid: Having one copy of each chromosome. In humans, the germ cells are normally haploid whereas all other cells in the body are diploid.

Hereditary mutation: A gene change in reproductive cells (egg or sperm) that becomes incorporated in the DNA of every cell in the offspring’s body; also called germline mutation.

Heterochromatin: Regions of chromosomes that stain darkly under analysis and are thought to contain repetitive and inactive DNA.

Heterozygote: An individual who has two different alleles or forms of a gene in his/her two chromosome sets.

Homozygote: An individual who has the same alleles or forms of a gene in his/her two chromosome sets.

Hot spot: A part of a gene with a very high tendency to become mutated, either naturally or under the induction of a mutagen.

Human genome: The full collection of genes that produces a human being.

Human Genome Project: An international research effort aimed at identifying and sequencing every base in the human genome.

Huntington's disease: An adult-onset disease characterized by progressive mental and physical deterioration. It is caused by an inherited dominant gene mutation.

I

Immunoglobulin: Blood proteins produced by mature B cells that make up antibodies.

Imprinting: The phenomenon where genetic material is expressed differently when inherited from the mother than when inherited from the father.

In vitro: A biological experimental system performed outside of a living organism.

In vivo: In a living organism.

Inborn errors of metabolism: Inherited diseases resulting from alterations in genes that code for enzymes.

Insert: A DNA sequence that is placed into a vector using recombinant genetic engineering techniques. Vectors are used to stabilize, transport, and express the DNA insert.

Intron: The non-coding portions of genes that are found between coding exons. Sequences from introns are spliced out before the gene message is translated into protein.

J

K

Karyotype: A display of the chromosomes, ordered according to length.

Kilobase (Kb): One thousand DNA base pairs

L

Leukemia: A cancer of 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: A gene-hunting technique that attempts to locate a gene by identifying and tracing other traits that tend to be co-inherited with it.

Locus: The chromosomal location of a specific gene.

M

Macrophage: A type of immune cell that engulfs foreign microbes and displays them for T cells to destroy.

Megabase: One million base pairs.

Meiosis: The cell division process where haploid sex cells are formed from diploid germ cells.

Melanoma: A cancer that begins in skin cells called melanocytes and spreads to internal organs.

Messenger RNA (mRNA): A type of RNA that is generated from the transcription of a gene, or template DNA. Mature mRNA has intron sequences spliced out and serves as the intermediate template from which proteins are made.

Mismatch: The condition where DNA bases from one strand are not complementary to the bases from the other strand.

Mitochondria: Structures in the cytoplasm of cells that generate energy. Mitochondria also have their own unique DNA.

Mitosis: The cell division process in which two identical cells are produced from a single parent cell.

Molecular Genetics: The study of the structure and function of genes at a molecular level.

Molecule: A specific ordered arrangement of atoms; one molecule of any substance is the smallest physical unit of that particular substance.

Monosomy: A condition where only one copy of a specific chromosome is present.

Monozygotic (identical) twins: Genetically identical twins that originate when a developing embryo divides to form two separate but identical embryos.

Multifactorial: Describes traits or diseases that are the result of the interaction between multiple genetic and environmental factors. A good example is heart disease.

Mutagen: A substance that causes mutation.

Mutation: An alteration in DNA sequence that is either induced by a mutagen or is spontaneous.

N

Natural selection: An evolutionary process where individuals with favorable genetic characteristics produce relatively greater numbers of surviving offspring.

Newborn screening: The examination of blood samples from a newborn infant to detect disease-related abnormalities or deficiencies in gene products.

Nucleotide: The basic unit of DNA or RNA, consisting of one chemical base, a phosphate group, and a sugar molecule.

Nucleus: The cell structure that houses the chromosomes.

O

Oncogenes: The mutated form of a cellular growth control gene, and a step in the formation of a tumor.

P

p53: A tumor suppressor gene that is mutated in many human cancers and results in the loss of a cell’s ability to check for DNA damage.

Pedigree: A diagram that displays family relationships, gender, disease status, and other attributes.

Penetrance: The proportion of individuals who carry a disease-causing gene that actually exhibit the disease symptoms.

Phenotype: The observed characteristics of an individual that are the result of genes and environmental influences.

Phenylketonuria (PKU): A disease in which the enzyme that metabolizes the amino acid phenylalanine is not expressed, resulting in abnormally high levels of phenylalanine. If left untreated, PKU can lead to severe, progressive mental retardation.

Physical mapping: The determination of physical distances between genes on chromosomes.

Plasmid: A circular piece of DNA found in bacteria that is capable of replicating independently. Plasmids are often used as cloning vectors to carry and express genes because they are easy to manipulate.

Polymerase chain reaction (PCR): An laboratory technique for amplifying a large number of copies of a specific DNA segment flanked with two known target sequences called primers.

Polymorphism: A highly variable chromosomal region where many different alleles of the same gene exist in different people within a population.

Population genetics: A field of genetics that studies genetic variation and genetic evolution of populations.

Population screening: The large-scale testing of populations for disease.

Prenatal diagnosis: The examination of fetal cells taken from an unborn fetus for biochemical, chromosomal, or gene alterations.

Proband: The first person in a pedigree to be clinically identified as having a disease in question.

Probe: A labeled segment of DNA that is used to bind to and identify a gene or mRNA transcript.

Promoter: A region of DNA, usually in front of a gene, that helps regulate that gene’s expression.

Proofreading: The correction of errors that occur during DNA replication, RNA transcription, and protein synthesis.

Protein: Complex molecules composed of amino acids that are essential to an organism’s structure and function. The sequence of a protein’s amino acids and thus the structure and function of the protein is determined by the DNA sequence of the gene that encodes it.

Q

R

Reading frame: A codon sequence that is comprised from reading DNA bases in groups of three from a specific start site, usually the beginning of a gene. Insertion or deletion mutations to a gene’s DNA sequence thus disrupt the normal reading frame.

Recessive allele: A gene that is expressed only when its counterpart allele on the matching chromosome is also recessive (not dominant). Autosomal recessive disorders develop in persons who receive two copies of the mutant gene, one from each parent who is a carrier. (See Dominant allele.)

Recombination: A phenomenon, also known as crossing over, where genetic material is physically exchanged by paired chromosomes, usually during the formation of sperm and egg cells (meiosis).

Replication: The process in which double-stranded DNA is replicated.

Reproductive cells: Egg and sperm cells. Each mature reproductive cell carries a single set of 23 chromosomes: 22 autosomal chromosomes and either an X or a Y chromosome.

Restriction enzymes: An enzyme that recognizes and cleaves DNA at specific sequences. They are useful to scientists for analyzing gene structure and mutations.

Restriction fragment length polymorphism (RFLP): The detection of variations in DNA sequence in populations by cleaving DNA with restriction enzymes and analyzing the patterns of the resulting DNA fragments.

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.

Retrovirus: A type of virus that is capable of inserting its DNA into its host cell’s genome and residing there indefinitely. Engineered retroviruses are a potential vector for gene therapy.

RNA: A chemical similar to DNA. The four bases contained within RNA are adenine, uracil, cytosine, and guanine (A,U,C,G). Adenine forms base pairs with uracil in RNA (as opposed to thymine in DNA). RNA also has a different type of sugar than DNA. RNA molecules are absolutely essential for protein synthesis and the cell’s reading of the genetic code.

S

Sarcoma: A type of cancer that starts in bone or muscle.

Screening: Looking for evidence of a particular disease such as cancer in persons with no symptoms of disease.

Sex chromosomes: The X and Y chromosomes in humans that determine sex. Human females have two X chromosomes; males have one X and one Y.

Sickle-cell anemia: An inherited, potentially lethal disease in which a defect in hemoglobin, the oxygen-carrying pigment in blood, causes distortion (sickling) and loss of functional red blood cells. This in turn causes damage to organs throughout the body.

Single gene disorder/trait: A disease or feature that is caused by a single gene, in contrast to multifactorial conditions.

Somatic cells: All body cells except the reproductive cells. In humans, most somatic cells are diploid.

Somatic mutations: A mutation that is not genetically acquired from an individual’s parents, but rather is acquired during life either spontaneously or through the induction of a mutagen.

Splicing: The process that removes introns and joins exons together contiguously in RNA

T

T cell (lymphocyte): A class of immune cells that help to bind and display foreign microbes or to destroy them.

Tay-Sachs disease: An inherited disease of infancy characterized by profound mental retardation and early death; it is caused by a recessive gene mutation.

Telomere: The ends of chromosomes that are normally slightly shortened after each round of cell division. Telomeres are thought to help stabilize chromosomes, and when they become too short after many cell divisions, the cell is no longer able to divide.

Thymine: One of the four DNA bases that encode genes. (Abbreviation: T) Normally pairs with an adenine base to form an A:T base pair.

Transcription: A biochemical process underlying the flow of genetic information: the process of copying a particular sequence of DNA (usually a gene) into a complimentary molecule of RNA. This RNA copy is called messenger RNA (mRNA). The mRNA then carries this genetic information to the cytoplasm where it serves as the blueprint for the synthesis of a protein by other protein machinery. (See also translation).

Translation: The process of turning instructions from mRNA, base by base, into a chain of amino acids. This chain then folds into a functional protein with the aid of other proteins. This process takes place on structures called ribosomes which are either located in the cytoplasm or in other cellular compartments.

Tumor-suppressor genes: Genes that normally restrain cell growth but, when missing or inactivated by mutation, allow unrestrained cell growth.

U

Uracil: A base present in RNA in place of thymine that is found in DNA. Uracil normally pairs with adenine to form A:U base pairs in RNA.

V

W

Wilms' tumor: A kidney cancer (tumor) that occurs in children, usually before age 5.

X

X chromosome: A sex chromosome; normal females carry two X chromosomes.

X-inactivation: The normal process in which one X chromosome in each cell of the female embryo is inactivated.

X-linked: Refers to genes that are located on the X-chromosome

Y

Y chromosome: A sex chromosome; normal males carry one Y and one X chromosome. In humans, the presence of a Y chromosome confers male characteristics while its absence confers female attributes.

Z

Zygote: The cell formed by the fusion of an egg and a sperm. This diploid cell will divide and eventually develop into a complex multicellular organism.