A

Acquired genetic mutation
See: somatic cell genetic mutation

Additive genetic effects
When the combined effects of alleles at different loci are equal to the sum of their individual effects.
See also: anticipation, complex trait

Adenine (A)
A nitrogenous base, one member of the base pair AT (adenine-thymine).
See also: base pair, nucleotide

Affected relative pair
Individuals related by blood, each of whom is affected with the same trait. Examples are affected sibling, cousin, and avuncular pairs.
See also: avuncular relationship

Aggregation technique
A technique used in model organism studies in which embryos at the 8-cell stage of development are pushed together to yield a single embryo (used as an alternative to microinjection).
See also: model organisms

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).
See also: locus, gene expression

Allogeneic
Variation in alleles among members of the same species.

Alternative splicing
Different ways of combining a gene's exons to make variants of the complete protein

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.

Amplification
An increase in the number of copies of a specific DNA fragment; can be in vivo or in vitro.
See also: cloning, polymerase chain reaction

Animal model
See: model organisms

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.
See also: bioinformatics

Anticipation
Each generation of offspring has increased severity of a genetic disorder; e.g., a grandchild may have earlier onset and more severe symptoms than the parent, who had earlier onset than the grandparent.
See also: additive genetic effects, complex trait

Antisense
Nucleic acid that has a sequence exactly opposite to an mRNA molecule made by the body; binds to the mRNA molecule to prevent a protein from being made.
See also: transcription

Apoptosis
Programmed cell death, the body's normal method of disposing of damaged, unwanted, or unneeded cells.
See also: cell

Arrayed library
Individual primary recombinant clones (hosted in phage, cosmid, YAC, or other vector) that are placed in two-dimensional arrays in microtiter dishes. Each primary clone can be identified by the identity of the plate and the clone location (row and column) on that plate. Arrayed libraries of clones can be used for many applications, including screening for a specific gene or genomic region of interest.
See also: library, genomic library, gene chip technology

Assembly
Putting sequenced fragments of DNA into their correct chromosomal positions.

Autoradiography
A technique that uses X-ray film to visualize radioactively labeled molecules or fragments of molecules; used in analyzing length and number of DNA fragments after they are separated by gel electrophoresis.

Autosomal dominant
A gene on one of the non-sex chromosomes that is always expressed, even if only one copy is present. The chance of passing the gene to offspring is 50% for each pregnancy.
See also: autosome, dominant, gene

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).
See also: sex chromosome

Avuncular relationship
The genetic relationship between nieces and nephews and their aunts and uncles.
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B

Backcross
A cross between an animal that is heterozygous for alleles obtained from two parental strains and a second animal from one of those parental strains. Also used to describe the breeding protocol of an outcross followed by a backcross.
See also: model organisms

Bacterial artificial chromosome (BAC)
A vector used to clone DNA fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli cells. Based on naturally occurring F-factor plasmid found in the bacterium E. coli.
See also: cloning vector

Bacteriophage
See: phage

Base
One of the molecules that form DNA and RNA molecules.
See also: nucleotide, base pair, base sequence

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.

Base sequence
The order of nucleotide bases in a DNA molecule; determines structure of proteins encoded by that DNA.

Base sequence analysis
A method, sometimes automated, for determining the base sequence.

Behavioral genetics
The study of genes that may influence behavior.

Bioinformatics
The science of managing and analyzing biological data using advanced computing techniques. Especially important in analyzing genomic research data.
See also: informatics

Bioremediation
The use of biological organisms such as plants or microbes to aid in removing hazardous substances from an area.

Biotechnology
A set of biological techniques developed through basic research and now applied to research and product development. In particular, biotechnology refers to the use by industry of recombinant DNA, cell fusion, and new bioprocessing techniques.

Birth defect
Any harmful trait, physical or biochemical, present at birth, whether a result of a genetic mutation or some other nongenetic factor.
See also: congenital, gene, mutation, syndrome

BLAST
A computer program that identifies homologous (similar) genes in different organisms, such as human, fruit fly, or nematode.
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C

Cancer
Diseases in which abnormal cells divide and grow unchecked. Cancer can spread from its original site to other parts of the body and can be fatal.
See also: hereditary cancer, sporadic cancer

Candidate gene
A gene located in a chromosome region suspected of being involved in a disease.
See also: positional cloning, protein

Capillary array
Gel-filled silica capillaries used to separate fragments for DNA sequencing. The small diameter of the capillaries permit the application of higher electric fields, providing high speed, high throughput separations that are significantly faster than traditional slab gels.

Carcinogen
Something which causes cancer to occur by causing changes in a cell's DNA.
See also: mutagene

Carrier
An individual who possesses an unexpressed, recessive trait.

cDNA library
A collection of DNA sequences that code for genes. The sequences are generated in the laboratory from mRNA sequences.
See also: messenger RNA

Cell
The basic unit of any living organism that carries on the biochemical processes of life.
See also: genome, nucleus

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.
See also: megabase

Centromere
A specialized chromosome region to which spindle fibers attach during cell division.

Chimera (pl. chimaera)
An organism that contains cells or tissues with a different genotype. These can be mutated cells of the host organism or cells from a different organism or species.

Chimeraplasty
An experimental targeted repair process in which a desirable sequence of DNA is combined with RNA to form a chimeraplast. These molecules bind selectively to the target DNA. Once bound, the chimeraplast activates a naturally occurring gene-correcting mechanism. Does not use viral or other conventional gene-delivery vectors.
See also: gene therapy, cloning vector

Chloroplast chromosome
Circular DNA found in the photosynthesizing organelle (chloroplast) of plants instead of the cell nucleus where most genetic material is located.

Chromomere
One of the serially aligned beads or granules of a eukaryotic chromosome, resulting from local coiling of a continuous DNA thread.

Chromosomal deletion
The loss of part of a chromosome's DNA.

Chromosomal inversion
Chromosome segments that have been turned 180 degrees. The gene sequence for the segment is reversed with respect to the rest of the chromosome.

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.

Chromosome painting
Attachment of certain fluorescent dyes to targeted parts of the chromosome. Used as a diagnositic for particular diseases, e.g. types of leukemia.

Chromosome region p
A designation for the short arm of a chromosome.

Chromosome region q
A designation for the long arm of a chromosome.

Clone
An exact copy made of biological material such as a DNA segment (e.

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