A nitrogenous base, one member of the base pair AT (adenine-thymine).
(Definition from Genomics and Its Impact on Science and Society website)
Allele
Alternative form of a genetic locus; a single allele for each locus is inherited from each parent (e.g., at a locus for eye color the allele might result in blue or brown eyes).
(Definition from Genomics and Its Impact on Science and Society website)
Amino acid
Any of a class of 20 molecules that are combined to form proteins in living things. The sequence of amino acids in a protein and hence protein function are determined by the genetic code
(Definition from Genomics and Its Impact on Science and Society website)
Annotation
Adding pertinent information such as gene coded for, amino acid sequence, or other commentary to the database entry of raw sequence of DNA bases.
(Definition from Genomics and Its Impact on Science and Society website)
Autosome
A chromosome not involved in sex determination. The diploid human genome consists of a total of 46 chromosomes: 22 pairs of autosomes, and 1 pair of sex chromosomes (the X and Y chromosomes)
(Definition from Genomics and Its Impact on Science and Society website)
B
Base pair (bp)
Two nitrogenous bases (adenine and thymine or guanine and cytosine) held together by weak bonds. Two strands of DNA are held together in the shape of a double helix by the bonds between base pairs.
(Definition from Genomics and Its Impact on Science and Society website)
Bioinformatics
The science of managing and analyzing biological data using advanced computing techniques. Especially important in analyzing genomic research data.
(Definition from Genomics and Its Impact on Science and Society website)
Basic Local Alignment Search Tool. (Altschul et al.) A sequence comparison algorithm optimized for speed used to search sequence databases for optimal local alignments to a query. The initial search is done for a word of length "W" that scores at least "T" when compared to the query using a substitution matrix. Word hits are then extended in either direction in an attempt to generate an alignment with a score exceeding the threshold of "S". The "T" parameter dictates the speed and sensitivity of the search. For additional details, see one of the BLAST tutorials (Query or BLAST) or the narrative guide to BLAST.
(Definition from National Center for Biotechnology Information website)
C
Candidate gene
A gene located in a chromosome region suspected of being involved in a disease.
(Definition from Genomics and Its Impact on Science and Society website)
Cell
The basic unit of any living organism that carries on the biochemical processes of life.
(Definition from Genomics and Its Impact on Science and Society website)
Centimorgan (cM)
A unit of measure of recombination frequency. One centimorgan is equal to a 1% chance that a marker at one genetic locus will be separated from a marker at a second locus due to crossing over in a single generation. In human beings, one centimorgan is equivalent, on average, to one million base pairs.
(Definition from Genomics and Its Impact on Science and Society website)
Chromosome
The self-replicating genetic structure of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins.
(Definition from Genomics and Its Impact on Science and Society website)
Chromosome region p
A designation for the short arm of a chromosome.
(Definition from Genomics and Its Impact on Science and Society website)
Chromosome region q
A designation for the long arm of a chromosome.
(Definition from Genomics and Its Impact on Science and Society website)
Clone
An exact copy made of biological material such as a DNA segment (e.g., a gene or other region), a whole cell, or a complete organism.
(Definition from Genomics and Its Impact on Science and Society website)
A base sequence in a DNA molecule (or an amino acid sequence in a protein) that has remained essentially unchanged throughout evolution.
(Definition from Genomics and Its Impact on Science and Society website)
Contig map
A map depicting the relative order of a linked library of overlapping clones representing a complete chromosomal segment.
(Definition from Genomics and Its Impact on Science and Society website)
Crossing over
The breaking during meiosis of one maternal and one paternal chromosome, the exchange of corresponding sections of DNA, and the rejoining of the chromosomes. This process can result in an exchange of alleles between chromosomes.
(Definition from Genomics and Its Impact on Science and Society website)
Cytosine (C)
A nitrogenous base, one member of the base pair GC (guanine and cytosine) in DNA.
(Definition from Genomics and Its Impact on Science and Society website)
D
Deletion
A loss of part of the DNA from a chromosome; can lead to a disease or abnormality.
(Definition from Genomics and Its Impact on Science and Society website)
Diploid
A full set of genetic material consisting of paired chromosomes, one from each parental set. Most animal cells except the gametes have a diploid set of chromosomes. The diploid human genome has 46 chromosomes.
(Definition from Genomics and Its Impact on Science and Society website)
Disease-associated genes
Alleles carrying particular DNA sequences associated with the presence of disease.
(Definition from Genomics and Its Impact on Science and Society website)
The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.
(Definition from Genomics and Its Impact on Science and Society website)
The use of existing DNA as a template for the synthesis of new DNA strands. In humans and other eukaryotes, replication occurs in the cell nucleus.
(Definition from Genomics and Its Impact on Science and Society website)
The relative order of base pairs, whether in a DNA fragment, gene, chromosome, or an entire genome.
(Definition from Genomics and Its Impact on Science and Society website)
Domain
A discrete portion of a protein with its own function. The combination of domains in a single protein determines its overall function.
(Definition from Genomics and Its Impact on Science and Society website)
Draft sequence
The sequence generated by the HGP as of June 2000 that, while incomplete, offers a virtual road map to an estimated 95% of all human genes. Draft sequence data are mostly in the form of 10,000 base pair-sized fragments whose approximate chromosomal locations are known.
(Definition from Genomics and Its Impact on Science and Society website)
E
Enzyme
A protein that acts as a catalyst, speeding the rate at which a biochemical reaction proceeds but not altering the direction or nature of the reaction.
(Definition from Genomics and Its Impact on Science and Society website)
Eukaryote
Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and bluegreen algae.
(Definition from Genomics and Its Impact on Science and Society website)
Exon
The protein-coding DNA sequence of a gene.
(Definition from Genomics and Its Impact on Science and Society website)
G
Gene
The fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides located in a particular position on a particular chromosome that encodes a specific functional product (i.e., a protein or RNA molecule).
(Definition from Genomics and Its Impact on Science and Society website)
Gene expression
The process by which a gene's coded information is converted into the structures present and operating in the cell. Expressed genes include those that are transcribed into mRNA and then translated into protein and those that are transcribed into RNA but not translated into protein (e.g., transfer and ribosomal RNAs).
(Definition from Genomics and Its Impact on Science and Society website)
Genetic code
The sequence of nucleotides, coded in triplets (codons) along the mRNA, that determines the sequence of amino acids in protein synthesis. A gene's DNA sequence can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence.
(Definition from Genomics and Its Impact on Science and Society website)
Genetic counseling
Provides patients and their families with education and information about genetic-related conditions and helps them make informed decisions.
(Definition from Genomics and Its Impact on Science and Society website)
Genetic linkage
The proximity of two or more markers (e.g., genes, RFLP markers) on a chromosome; the closer the markers, the lower the probability that they will be separated during DNA repair or replication processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes), and hence the greater the probability that they will be inherited together.
(Definition from Genomics and Its Impact on Science and Society website)
Genetic polymorphism
Difference in DNA sequence among individuals that may underlie differences in health. Genetic variations occurring in more than 1% of a population would be considered useful polymorphisms for genetic linkage analysis.
(Definition from Genomics and Its Impact on Science and Society website)
Genome
All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.
(Definition from Genomics and Its Impact on Science and Society website)
Genomic library
A collection of clones made from a set of randomly generated overlapping DNA fragments that represent the entire genome of an organism.
(Definition from Genomics and Its Impact on Science and Society website)
Genotype
The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype).
(Definition from Genomics and Its Impact on Science and Society website)
Guanine (G)
A nitrogenous base, one member of the base pair GC (guanine and cytosine) in DNA.
(Definition from Genomics and Its Impact on Science and Society website)
H
Haploid
A single set of chromosomes (half the full set of genetic material) present in the egg and sperm cells of animals and in the egg and pollen cells of plants. Human beings have 23 chromosomes in their reproductive cells.
(Definition from Genomics and Its Impact on Science and Society website)
Heterozygosity
The presence of different alleles at one or more loci on homologous chromosomes.
(Definition from Genomics and Its Impact on Science and Society website)
The presence of different alleles at one or more loci on homologous chromosomes.
A short stretch of nucleotides whose base sequence is virtually identical in all the genes that contain it. Homeoboxes have been found in many organisms from fruit flies to human beings. In the fruit fly, a homeobox appears to determine when particular groups of genes are expressed during development.
(Definition from Genomics and Its Impact on Science and Society website)
Homology
Similarity in DNA or protein sequences between individuals of the same species or among different species.
(Definition from Genomics and Its Impact on Science and Society website)
Homozygote
An organism that has two identical alleles of a gene.
(Definition from Genomics and Its Impact on Science and Society website)
DNA sequence that interrupts the protein-coding sequence of a gene; an intron is transcribed into RNA but is cut out of the message before it is translated into protein.
(Definition from Genomics and Its Impact on Science and Society website)
Stretches of DNA that do not code for genes; most of the genome consists of so-called junk DNA which may have regulatory and other functions. Also called non-coding DNA.
(Definition from Genomics and Its Impact on Science and Society website)
K
Kilobase (kb)
Unit of length for DNA fragments equal to 1000 nucleotides.
(Definition from Genomics and Its Impact on Science and Society website)
L
Linkage map
A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the loci are inherited together. Distance is measured in centimorgans (cM).
(Definition from Genomics and Its Impact on Science and Society website)
Locus
The position on a chromosome of a gene or other chromosome marker; also, the DNA at that position. The use of locus is sometimes restricted to mean expressed DNA regions.
(Definition from Genomics and Its Impact on Science and Society website)
M
Mapping
Determination of the relative positions of genes on a DNA molecule (chromosome or plasmid) and of the distance, in linkage units or physical units, between them.
(Definition from Genomics and Its Impact on Science and Society website)
Megabase (Mb)
Unit of length for DNA fragments equal to 1 million nucleotides and roughly equal to 1 cM.
(Definition from Genomics and Its Impact on Science and Society website)
Meiosis
The process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells, each with a haploid set of chromosomes.
(Definition from Genomics and Its Impact on Science and Society website)
Mitosis
The process of nuclear division in cells that produces daughter cells that are genetically identical to each other and to the parent cell.
(Definition from Genomics and Its Impact on Science and Society website)
Model organism
A laboratory animal or other organism useful for research.
(Definition from Genomics and Its Impact on Science and Society website)
Mutation
Any heritable change in DNA sequence.
(Definition from Genomics and Its Impact on Science and Society website)
N
Nitrogenous base
A nitrogen-containing molecule having the chemical properties of a base. DNA contains the nitrogenous bases adenine (A), guanine (G), cytosine (C), and thymine (T).
(Definition from Genomics and Its Impact on Science and Society website)
Nucleotide
A subunit of DNA or RNA consisting of a nitrogenous base (adenine, guanine, thymine, or cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Thousands of nucleotides are linked to form a DNA or RNA molecule.
(Definition from Genomics and Its Impact on Science and Society website)
O
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).
(Definition from Genomics and Its Impact on Science and Society website)
P
Pedigree
A family tree diagram that shows how a particular genetic trait or disease has been inherited.
(Definition from Genomics and Its Impact on Science and Society website)
Phenotype
The physical characteristics of an organism or the presence of a disease that may or may not be genetic.
(Definition from Genomics and Its Impact on Science and Society website)
Physical map
A map of the locations of identifiable landmarks on DNA (e.g., restriction-enzyme cutting sites, genes), regardless of inheritance. Distance is measured in base pairs. For the human genome, the lowest-resolution physical map is the banding patterns on the 24 different chromosomes; the highest-resolution map is the complete nucleotide sequence of the chromosomes.
(Definition from Genomics and Its Impact on Science and Society website)
A method for amplifying a DNA base sequence using a heat-stable polymerase and two 20-base primers, one complementary to the (+) strand at one end of the sequence to be amplified and one complementary to the (-) strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same primer sequences, successive rounds of primer annealing, strand elongation, and dissociation produce rapid and highly specific amplification of the desired sequence. PCR also can be used to detect the existence of the defined sequence in a DNA sample.
(Definition from Genomics and Its Impact on Science and Society website)
Enzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from deoxyribonucleotides.
(Definition from Genomics and Its Impact on Science and Society website)
Positional cloning
A technique used to identify genes, usually those that are associated with diseases, based on their location on a chromosome.
(Definition from Genomics and Its Impact on Science and Society website)
Promoter
A DNA site to which RNA polymerase will bind and initiate transcription.
(Definition from Genomics and Its Impact on Science and Society website)
Protein
A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene that codes for the protein. Proteins are required for the structure, function, and regulation of the body's cells, tissues, and organs; and each protein has unique functions. Examples are hormones, enzymes, and antibodies.
(Definition from Genomics and Its Impact on Science and Society website)
R
Recessive gene
A gene which will be expressed only if there are 2 identical copies or, for a male, if one copy is present on the X chromosome.
(Definition from Genomics and Its Impact on Science and Society website)
A chemical found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell. The structure of RNA is similar to that of DNA. There are several classes of RNA molecules, including messenger RNA, transfer RNA, ribosomal RNA, and other small RNAs, each serving a different purpose.
(Definition from Genomics and Its Impact on Science and Society website)
S
Sequencing
Determination of the order of nucleotides (base sequences) in a DNA or RNA molecule or the order of amino acids in a protein.
(Definition from Genomics and Its Impact on Science and Society website)
Multiple copies of the same base sequence on a chromosome; used as markers in physical mapping.
(Definition from Genomics and Its Impact on Science and Society website)
Thymine (T)
A nitrogenous base, one member of the base pair AT (adenine-thymine).
(Definition from Genomics and Its Impact on Science and Society website)
Transcription
The synthesis of an RNA copy from a sequence of DNA (a gene); the first step in gene expression.
(Definition from Genomics and Its Impact on Science and Society website)
Transcription factor
A protein that binds to regulatory regions and helps control gene expression.
(Definition from Genomics and Its Impact on Science and Society website)
A class of RNA having structures with triplet nucleotide sequences that are complementary to the triplet nucleotide coding sequences of mRNA. The role of tRNAs in protein synthesis is to bond with amino acids and transfer them to the ribosomes, where proteins are assembled according to the genetic code carried by mRNA.
(Definition from Genomics and Its Impact on Science and Society website)
Translation
The process in which the genetic code carried by mRNA directs the synthesis of proteins from amino acids.
(Definition from Genomics and Its Impact on Science and Society website)
U
Uracil
A nitrogenous base normally found in RNA but not DNA; uracil is capable of forming a base pair with adenine.
(Definition from Genomics and Its Impact on Science and Society website)
