Niemann-Pick disease, type C (NPC)A disease that causes progressive deterioration of the nervous system by blocking movement of cholesterol within cells.
Nitrogenous baseThe purines (adenine and guanine) and pyrimidines (cytosine, and thymine or uracil ) that are present in DNA and RNA.
non-coding DNAThe strand of DNA that does not carry the information necessary to make a protein.
non-directivenessThe process by which genetic counselors advise clients toward a certain test or outcome, particularly related to child-bearing issues, without pressure or…
nonsense mutationA mutation which converts an amino-acid-specifying codon into a stop codon, e.g.
Northern blotA technique analogous to Southern blotting, but involving the transfer of RNA from an to a membrane, prior to probing.
Nuclear transferA technology by which novel animals are generated by cloning a single diploid somatic cell.
Nucleic acidA macromolecule consisting of polymerized nucleotides . Two forms are found, DNA and RNA.
Nucleotide(NOO-klee-oh-TIDE) A building block for nucleic acids (the molecules inside cells that carry genetic information).
Nucleus(NOO-klee-us) In biology, the structure in a cell that contains the chromosomes.
OligoOligonucleotide, short sequence of single-stranded DNA or RNA. Oligos are often used as probes for detecting complementary DNA or RNA because they bind…
OligogenicA phenotypic trait produced by two or more genes working together. See also: polygenic disorder
OligonucleotideA DNA polymer composed of only a few nucleotides. (See Nucleotide.)
oncogeneA gene that normally directs cell growth. If altered, an oncogene can promote or allow the uncontrolled growth of cancer.
oncovirusA class of retroviruses that cause a cell to become cancerous. See also cell, retrovirus, cancer, gene
Open reading frame (ORF)The sequence of DNA or RNA located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon).
OperonA functionally integrated genetic unit for the control of gene expression in bacteria.
P1-derived artificial chromosome (PAC)One type of vector used to clone DNA fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli cells.
p53A gene which normally regulates the cell cycle and protects the cell from damage to its genome.
Parkinson's diseaseA common progressive neurological disorder that results from degeneration of nerve cells in a region of the brain that controls movement.
patentA grant to an inventor of the right to exclude others, for a limited time, from making, using, or selling his invention in the United States.
pedigreeA record of one's ancestors, offspring, siblings, and their offspring that may be used to determine the pattern of certain genes or disease inheritance…
PenetranceThe proportion of individuals in a population that express the phenotype expected from their genotype with respect to a specific gene.
peptideAny compound consisting of two or more amino acids, the building blocks of proteins.
PharmacogenomicsThe study of the interaction of an individual's genetic makeup and response to a drug.
PhenocopyAn environmentally induced, non hereditary variation in an organism, resembling a genetically determined trait.
PhenotypeThe observable characteristics of an organism, the expression of gene alleles (genotype) as an observable physical or biochemical trait. See Genotype.
Physical mapA map showing physical locations on a DNA molecule, such as restriction sites, and sequence-tagged sites. (See Mapping.)
PlasmidAn circular self-replicating non-chromosomal DNA molecule found in many bacteria, capable of transfer between bacterial cells of the same species, and…
PleiotropyThe simultaneous effect of a given gene on more than one apparently unrelated trait.
PluripotencyThe potential of a cell to develop into more than one type of mature cell, depending on environment.
polydactylyAn abnormality in which a person is born with more than the normal number of fingers or toes. See also
Polygenic disorderGenetic disorder resulting from the combined action of alleles of more than one gene (e.g., heart disease, diabetes, and some cancers).
Polymerase, DNA or RNAEnzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from…
polymorphism(PAH-lee-MOR-fih-zum) A common variation or mutation in DNA.
PolypeptideA linear polymer composed of covalently linked amino acids. Each link is formed by a single peptide bond.
Population geneticsThe branch of genetics that deals with frequencies of alleles and genotypes in breeding populations.
positional cloningA strategy for gene cloning that relies on the identification of closely linked markers to the target trait, and then uses chromosome walking to identify…
primary immunodeficiencyA group of rare inherited disorders of the immune system, including adenosine deaminase deficiency, severe combined immunodeficiency (SCID), and…
PrimerA short DNA or RNA fragment annealed to single-stranded DNA, from which DNA polymerase extends a new DNA strand to produce a duplex molecule.
PrivacyIn genetics, the right of people to restrict access to their genetic information.
ProbeA sequence of DNA or RNA, labeled or marked with a radioactive isotope, used to detect the presence of complementary nucleotide sequences. See Nucleotide.
ProkaryoteA bacterial cell lacking a true nucleus; its DNA is usually in one long strand. See Eukaryote.
PromoterAny person who, directly or indirectly, organizes or assists in the organization of a tax shelter or who participates in the sale of any interests in a…
PronucleusEither of the two haploid gamete nuclei just prior to their fusion in the fertilized ovum.
prostate cancer(PROS-tayt KAN-ser) Cancer that forms in tissues of the prostate (a gland in the male reproductive system found below the bladder and in front of the…
proteaseAn enzyme that cleaves peptide bonds that link amino acids in protein molecules.
protein(PRO-teen) A molecule made up of amino acids that are needed for the body to function properly.
ProteomeThe complete complement of proteins made by a given species in all its tissues and growth stages.
proteomicsThe study of the structure and function of proteins, including the way they work and interact with each other inside cells.
pseudogeneAn incomplete or mutated copy of a gene which is not transcribed because it lacks a continuous open reading frame.
PurineA double-ring, nitrogen-containing base present in nucleic acids . Adenine (A) and guanine (G) are the two purines normally present in DNA and RNA…
PyrimidineA single-ring, nitrogen-containing base present in nucleic acid s. Cytosine (C) and thymine (T) are present in DNA, whereas uracil (U) replaces T in RNA.
Radiation hybridA hybrid cell containing small fragments of irradiated human chromosomes. Maps of irradiation sites on chromosomes for the human, rat, mouse, and other…
recessiveDescribing an allele whose effect with respect to a particular trait is not evident in heterozygotes. Opposite: dominant.
Recessive geneCharacterized as having a phenotype expressed only when both copies of the gene are mutated or missing.
Reciprocal translocationWhen a pair of chromosomes exchange exactly the same length and area of DNA. Results in a shuffling of genes.
Recombinant cloneClone containing recombinant DNA molecules. See also: recombinant DNA technology
recombinant DNAThe process of cutting and recombining DNA fragments from different sources as a means to isolate genes or to alter their structure and function.
Recombinant DNA moleculesA combination of DNA molecules of different origin that are joined using recombinant DNA technologies.
Recombinant DNA technologyA set of techniques for manipulating DNA, including: the identification and cloning of genes; the study of the expression of cloned genes; and the…
RecombinationThe production of a DNA molecule with segments derived from more than one parent DNA molecule.
Repetitive DNADNA sequences that are present in a genome in many copies, some of it originating from retrotransposon activity.
Reporter geneA gene that encodes a product that can be readily assayed. Used as to confirm the incorporation of a transgene into, organ or tissue, and as a means of…
repressorA DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.
restriction enzymesEnzymes that recognize a specific sequence of double-stranded DNA and cut the DNA at that site.
Restriction fragment length polymorphism (RFLP)Differences in nucleotide sequence between alleles at a chromosomal locus result in restriction fragments of varying lengths detected by Southern analysis.
Restriction-enzyme cutting siteA specific nucleotide sequence of DNA at which a particular restriction enzyme cuts the DNA. Some sites occur frequently in DNA (e.g.
Retroviral infectionThe presence of retroviral vectors, such as some viruses, which use their recombinant DNA to insert their genetic material into the chromosomes of the…
retrovirus(REH-troh-VY-rus) A type of virus that has RNA instead of DNA as its genetic material.
Reverse transcriptaseAn enzyme that uses an RNA molecule as a template for the synthesis of a complementary DNA strand. Synonym: RNA -dependent DNA polymerase.
Ribonucleic acid (RNA)A chemical similar to a single strand of DNA. In RNA, the letter U, which stands for uracil, is substituted for T in the genetic code.
RiboseA monosaccharide found in all ribonucleosides, ribonucleotides and RNA. Its close analogue, 2-deoxyribose, is similarly found in all deoxyribonucleosides…
RibosomeCellular organelle that is the site of protein synthesis during translation. See Organelle, Translation.
RibosomesSmall cellular components composed of specialized ribosomal RNA and protein; site of protein synthesis. See also: RNA
risk communicationThe interactive exchange of information and opinions throughout the risk analysis process concerning hazards and risks, risk-related factors and risk…
RNA (Ribonucleic acid)An organic acid composed of re- peating nucleotide units of adenine, guanine, cytosine, and uracil, whose ribose components are linked by phosphodiester…
Sanger sequencingA widely used method of determining the order of bases in DNA. See also: sequencing, shotgun sequencing
satelliteA chromosomal segment that branches off from the rest of the chromosome but is still connected by a thin filament or stalk.
ScaffoldThe central protein aceous core structure of condensed eukaryotic chromosomes. The scaffold is composed of non-histone chromosomal protein s.
segregationFor genes, the separation of allele pairs from one another and their resulting assortment into different cells at meiosis.
sequenceThe linear order of nucleotides along a DNA or RNA molecule, and the process of obtaining this.
Sequence assemblyA process whereby the order of multiple sequenced DNA fragments is determined.
Sequence tagged site (STS)A unique (single-copy) DNA sequence used as a mapping landmark on a chromosome.
SequencingDetermination of the order of nucleotides (base sequences) in a DNA or RNA molecule or the order of amino acids in a protein.
Sequencing technologyThe instrumentation and procedures used to determine the order of nucleotides in DNA.
severe combined immunodeficiency (SCID)A disease affecting the immune system. SCID is fatal if affected individuals do not receive bone marrow transplants. See also antibody
sex chromosomeDifferentiated chromosome which is responsible for the determination of sex of the individual.
Sex-linkedLocated on the X chromosome. Sex-linked (or x-linked) diseases are generally seen only in males. See also gene, mutation