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page-title: Dictionary of Genetic Terms
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Dictionary of Genetic
Terms

Genomics and Its Impact on Medicine and Society: A 2001
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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.g., a gene or other region), a whole cell, or a complete
organism.

 Clone bank

See: genomic
library

 Cloning

Using specialized DNA technology to produce multiple, exact
copies of a single gene or other segment of DNA to obtain enough
material for further study. This process, used by researchers in
the Human Genome Project, is referred to as cloning DNA.  The
resulting cloned (copied) collections of DNA molecules are called
clone libraries. A second type of cloning exploits the natural
process of cell division to make many copies of an entire cell. The
genetic makeup of these cloned cells, called a cell line, is
identical to the original cell. A third type of cloning produces
complete, genetically identical animals such as the famous Scottish
sheep, Dolly. 
See also: cloning
vector

 Cloning
vector

DNA molecule originating from a virus, a plasmid, or the cell
of a higher organism into which another DNA fragment of appropriate
size can be integrated without loss of the vector's capacity for
self-replication; vectors introduce foreign DNA into host cells,
where the DNA can be reproduced in large quantities. Examples are
plasmids, cosmids, and yeast artificial chromosomes; vectors are
often recombinant molecules containing DNA sequences from several
sources.

 Code

See: genetic
code

Codominance

Situation in which two different alleles for a genetic trait
are both expressed.
See also: autosomal dominant,recessive gene

 Codon

See: genetic
code

Coisogenic or congenic

Nearly identical strains of an organism; they vary at only a
single locus.

Comparative genomics

The study of human genetics by comparisons with model organisms
such as mice, the fruit fly, and the bacterium E. coli.

Complementary DNA (cDNA)

DNA that is synthesized in the laboratory from a messenger RNA
template.

Complementary sequence

Nucleic acid base sequence that can form a double-stranded
structure with another DNA fragment by following base-pairing rules
(A pairs with T and C with G). The complementary sequence to GTAC
for example, is CATG.

 Complex
trait

Trait that has a genetic component that does not follow strict
Mendelian inheritance. May involve the interaction of two or more
genes or gene-environment interactions.
See also: Mendelian inheritance,additive genetic
effects

Computational biology

See: bioinformatics

Confidentiality

In genetics, the expectation that genetic material and the
information gained from testing that material will not be available
without the donor's consent.

Congenital

Any trait present at birth, whether the result of a genetic or
nongenetic factor.
See also: birth
defect

Conserved sequence

A base sequence in a DNA molecule (or an amino acid sequence in
a protein) that has remained essentially unchanged throughout
evolution.

Constitutive ablation

Gene expression that results in cell death.

 Contig

Group of cloned (copied) pieces of DNA representing overlapping
regions of a particular chromosome.

 Contig map

A map depicting the relative order of a linked library of
overlapping clones representing a complete chromosomal
segment.

 Cosmid

Artificially constructed cloning vector containing the cos gene
of phage lambda. Cosmids can be packaged in lambda phage particles
for infection into E. coli; this permits cloning of larger
DNA fragments (up to 45kb) than can be introduced into bacterial
hosts in plasmid vectors.

 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.
See also: recombination

Cytogenetics

The study of the physical appearance of chromosomes.
See also: karyotype

Cytological band

An area of the chromosome that stains differently from areas
around it.
See also: cytological map

Cytological map

A type of chromosome map whereby genes are located on the basis
of cytological findings obtained with the aid of chromosome
mutations.

 Cytoplasmic
(uniparental) inheritance

See: cytoplasmic trait

Cytoplasmic trait

A genetic characteristic in which the genes are found outside
the nucleus, in chloroplasts or mitochondria. Results in offspring
inheriting genetic material from only one parent.

 Cytosine (C)

A nitrogenous base, one member of the base pair GC (guanine and
cytosine) in DNA.
See also: base
pair,nucleotide

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D

 Data
warehouse

A collection of databases, data tables, and mechanisms to
access the data on a single subject.

 Deletion

A loss of part of the DNA from a chromosome; can lead to a
disease or abnormality.
See also: chromosome,mutation

 Deletion
map

A description of a specific chromosome that uses defined
mutations --specific deleted areas in the genome-- as 'biochemical
signposts,' or markers for specific areas.

Deoxyribonucleotide

See: nucleotide

Deoxyribose

A type of sugar that is one component of DNA (deoxyribonucleic
acid).

 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.
See also: haploid

Directed evolution

A laboratory process used on isolated molecules or microbes to
cause mutations and identify subsequent adaptations to novel
environments.

Directed mutagenesis

Alteration of DNA at a specific site and its reinsertion into
an organism to study any effects of the change.

Directed sequencing

Successively sequencing DNA from adjacent stretches of
chromosome.

 Disease-associated
genes

Alleles carrying particular DNA sequences associated with the
presence of disease.

 DNA (deoxyribonucleic
acid)

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.

 DNA bank

A service that stores DNA extracted from blood samples or other
human tissue.

 DNA probe

See: probe

 DNA repair
genes

Genes encoding proteins that correct errors in DNA
sequencing.

 DNA
replication

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.

 DNA
sequence

The relative order of base pairs, whether in a DNA fragment,
gene, chromosome, or an entire genome.
See also: base sequence analysis

 Domain

A discrete portion of a protein with its own function. The
combination of domains in a single protein determines its overall
function.

 Dominant

An allele that is almost always expressed, even if only one
copy is present.
See also: gene,genome

 Double
helix

The twisted-ladder shape that two linear strands of DNA assume
when complementary nucleotides on opposing strands bond
together.

 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.
See also: sequencing,finished DNA sequence,working draft DNA
sequence

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E

Electrophoresis

A method of separating large molecules (such as DNA fragments
or proteins) from a mixture of similar molecules. An electric
current is passed through a medium containing the mixture, and each
kind of molecule travels through the medium at a different rate,
depending on its electrical charge and size. Agarose and acrylamide
gels are the media commonly used for electrophoresis of proteins
and nucleic acids.

Electroporation

A process using high-voltage current to make cell membranes
permeable to allow the introduction of new DNA; commonly used in
recombinant DNA technology.
See also: transfection

 Embryonic stem (ES)
cells

An embryonic cell that can replicate indefinitely, transform
into other types of cells, and serve as a continuous source of new
cells.

Endonuclease

See: restriction enzyme

 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.

 Epistasis

One gene interfers with or prevents the expression of another
gene located at a different locus.

Escherichia coli

Common bacterium that has been studied intensively by
geneticists because of its small genome size, normal lack of
pathogenicity, and ease of growth in the laboratory.

 Eugenics

The study of improving a species by artificial selection;
usually refers to the selective breeding of humans.

 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.
See also: prokaryote,chromosome.

 Evolutionarily
conserved

See: conserved sequence

 Exogenous
DNA

DNA originating outside an organism that has been introducted
into the organism.

 Exon

The protein-coding DNA sequence of a gene.
See also: intron

Exonuclease

An enzyme that cleaves nucleotides sequentially from free ends
of a linear nucleic acid substrate.

 Expressed
gene

See: gene
expression

Expressed sequence tag (EST)

A short strand of DNA that is a part of a cDNA molecule and can
act as identifier of a gene. Used in locating and mapping
genes.
See also: cDNA,sequence tagged site

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F

 Filial
generation (F1, F2)

Each generation of offspring in a breeding program, designated
F1, F2, etc.

Fingerprinting

In genetics, the identification of multiple specific alleles on
a person's DNA to produce a unique identifier for that
person.
See also: forensics

Finished DNA Sequence

High-quality, low error, gap-free DNA sequence of the human
genome. Achieving this ultimate 2003 HGP goal requires additional
sequencing to close gaps, reduce ambiguities, and allow for only a
single error every 10,000 bases, the agreed-upon standard for HGP
finished sequence.
See also: sequencing,draft sequence

 Flow
cytometry

Analysis of biological material by detection of the
light-absorbing or fluorescing properties of cells or subcellular
fractions (i.e., chromosomes) passing in a narrow stream through a
laser beam. An absorbance or fluorescence profile of the sample is
produced. Automated sorting devices, used to fractionate samples,
sort successive droplets of the analyzed stream into different
fractions depending on the fluorescence emitted by each
droplet.

 Flow
karyotyping

Use of flow cytometry to analyze and separate chromosomes
according to their DNA content.

 Fluorescence in situ
hybridization (FISH)

A physical mapping approach that uses fluorescein tags to
detect hybridization of probes with metaphase chromosomes and with
the less-condensed somatic interphase chromatin.

 Forensics

The use of DNA for identification. Some examples of DNA use are
to establish paternity in child support cases; establish the
presence of a suspect at a crime scene, and identify accident
victims.

 Fraternal
twin

Siblings born at the same time as the result of fertilization
of two ova by two sperm. They share the same genetic relationship
to each other as any other siblings.
See also: identical twin

 Full
gene sequence

The complete order of bases in a gene. This order determines
which protein a gene will produce.

Functional genomics

The study of genes, their resulting proteins, and the role
played by the proteins the body's biochemical processes. 

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G

 Gamete

Mature male or female reproductive cell (sperm or ovum) with a
haploid set of chromosomes (23 for humans).

 GC-rich
area

Many DNA sequences carry long stretches of repeated G and C
which often indicate a gene-rich region.

Gel electrophoresis

See: electrophoresis

 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).
See also: gene
expression

 Gene
amplification

Repeated copying of a piece of DNA; a characteristic of tumor
cells.
See also: gene,oncogene

Gene chip technology

Development of cDNA microarrays from a large number of genes.
Used to monitor and measure changes in gene expression for each
gene represented on the chip.

 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).

 Gene
family

Group of closely related genes that make similar products.

 Gene
library

See: genomic
library

 Gene
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.

 Gene pool

All the variations of genes in a species.
See also: allele,gene,polymorphism

 Gene
prediction

Predictions of possible genes made by a computer program based
on how well a stretch of DNA sequence matches known gene
sequences

 Gene
product

The biochemical material, either RNA or protein, resulting from
expression of a gene. The amount of gene product is used to measure
how active a gene is; abnormal amounts can be correlated with
disease-causing alleles.

 Gene
testing

See: genetic
testing,genetic screening

 Gene
therapy

An experimental procedure aimed at replacing, manipulating, or
supplementing nonfunctional or misfunctioning genes with healthy
genes.
See also: gene,inherit,somatic cell gene therapy,germ line gene
therapy

 Gene
transfer

Incorporation of new DNA into and organism's cells, usually by
a vector such as a modified virus. Used in gene therapy.
See also: mutation,gene therapy,vector

 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.

Genetic counseling

Provides patients and their families with education and
information about genetic-related conditions and helps them make
informed decisions.

Genetic discrimination

Prejudice against those who have or are likely to develop an
inherited disorder.

Genetic engineering

Altering the genetic material of cells or organisms to enable
them to make new substances or perform new functions.

 Genetic engineering
technology

See: recombinant DNA technology

 Genetic
illness

Sickness, physical disability, or other disorder resulting from
the inheritance of one or more deleterious alleles.

Genetic informatics

See: bioinformatics

 Genetic
map

See: linkage
map

 Genetic
marker

A gene or other identifiable portion of DNA whose inheritance
can be followed.
See also: chromosome,DNA,gene,inherit

 Genetic
material

See: genome

 Genetic
mosaic

An organism in which different cells contain different genetic
sequence. This can be the result of a mutation during development
or fusion of embryos at an early developmental stage.

Genetic polymorphism

Difference in DNA sequence among individuals, groups, or
populations (e.g., genes for blue eyes versus brown eyes).

Genetic predisposition

Susceptibility to a genetic disease. May or may not result in
actual development of the disease.

Genetic screening

Testing a group of people to identify individuals at high risk
of having or passing on a specific genetic disorder.

 Genetic
testing

Analyzing an individual's genetic material to determine
predisposition to a particular health condition or to confirm a
diagnosis of genetic disease.

 Genetics

The study of inheritance patterns of specific traits.

 Genome

All the genetic material in the chromosomes of a particular
organism; its size is generally given as its total number of base
pairs.

 Genome
project

Research and technology-development effort aimed at mapping and
sequencing the genome of human beings and certain model
organisms.
See also: Human Genome Initiative

 Genomic
library

A collection of clones made from a set of randomly generated
overlapping DNA fragments that represent the entire genome of an
organism.
See also: library,arrayed library

 Genomic
sequence

See: DNA

 Genomics

The study of genes and their function.

 Genotype

The genetic constitution of an organism, as distinguished from
its physical appearance (its phenotype).

 Germ cell

Sperm and egg cells and their precursors. Germ cells are
haploid and have only one set of chromosomes (23 in all), while all
other cells have two copies (46 in all).

 Germ line

The continuation of a set of genetic information from one
generation to the next.
See also: inherit

Germ line gene therapy

An experimental process of inserting genes into germ cells or
fertilized eggs to cause a genetic change that can be passed on to
offspring. May be used to alleviate effects associated with a
genetic disease.
See also: genomics,somatic cell gene
therapy.

 Germ line genetic
mutation

See: mutation

 Guanine (G)

A nitrogenous base, one member of the base pair GC (guanine and
cytosine) in DNA.
See also: base
pair,nucleotide

Gyandromorph

Organisms that have both male and female cells and therefore
express both male and female characteristics. 

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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.
See also: diploid

 Haplotype

A way of denoting the collective genotype of a number of
closely linked loci on a chromosome.

Hemizygous

Having only one copy of a particular gene. For example, in
humans, males are hemizygous for genes found on the Y
chromosome.

Hereditary cancer

Cancer that occurs due to the inheritance of an altered gene
within a family.
See also: sporadic cancer

Heterozygosity

The presence of different alleles at one or more loci on
homologous chromosomes.

Heterozygote

See: heterozygosity

 Highly conserved
sequence

DNA sequence that is very similar across several different
types of organisms.
See also: gene,mutation

 High-throughput
sequencing

A fast method of determining the order of bases in DNA.
See also: sequencing

 Homeobox

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.

 Homolog

A member of a chromosome pair in diploid organisms or a gene
that has the same origin and functions in two or more species.

Homologous chromosome

Chromosome containing the same linear gene sequences as
another, each derived from one parent.

 Homologous
recombination

Swapping of DNA fragments between paired chromosomes.

 Homology

Similarity in DNA or protein sequences between individuals of
the same species or among different species.

Homozygote

An organism that has two identical alleles of a gene.
See also: heterozygote

Homozygous

See: homozygote

 Human artificial
chromosome (HAC)

A vector used to hold large DNA fragments.
See also: chromosome,DNA

 Human
gene therapy

See: gene
therapy

Human Genome Initiative

Collective name for several projects begun in 1986 by DOE to
create an ordered set of DNA segments from known chromosomal
locations, develop new computational methods for analyzing genetic
map and DNA sequence data, and develop new techniques and
instruments for detecting and analyzing DNA. This DOE initiative is
now known as the Human Genome Program. The joint national effort,
led by DOE and NIH, is known as the Human Genome Project.

Human Genome Project (HGP)

Formerly titled Human Genome Initiative.
See also: Human Genome Initiative

 Hybrid

The offspring of genetically different parents.
See also: heterozygote

Hybridization

The process of joining two complementary strands of DNA or one
each of DNA and RNA to form a double-stranded molecule. 

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I

 Identical
twin

Twins produced by the division of a single zygote; both have
identical genotypes.
See also: fraternal twin

Immunotherapy

Using the immune system to treat disease, for example, in the
development of vaccines. May also refer to the therapy of diseases
caused by the immune system.
See also: cancer

Imprinting

A phenomenon in which the disease phenotype depends on which
parent passed on the disease gene. For instance, both Prader-Willi
and Angelman syndromes are inherited when the same part of
chromosome 15 is missing. When the father's complement of 15 is
missing, the child has Prader-Willi, but when the mother's
complement of 15 is missing, the child has Angelman syndrome.

In situ hybridization

Use of a DNA or RNA probe to detect the presence of the
complementary DNA sequence in cloned bacterial or cultured
eukaryotic cells.

 In vitro

Studies performed outside a living organism such as in a
laboratory.

 In vivo

Studies carried out in living organisms.

Independent assortment

During meiosis each of the two copies of a gene is distributed
to the germ cells independently of the distribution of other
genes.
See also: linkage

Informatics

See: bioinformatics

 Informed
consent

An individual willingly agrees to participate in an activity
after first being advised of the risks and benefits.
See also: privacy

 Inherit

In genetics, to receive genetic material from parents through
biological processes.

 Inherited

See: inherit

 Insertion

A chromosome abnormality in which a piece of DNA is
incorporated into a gene and thereby disrupts the gene's normal
function.
See also: chromosome,DNA,gene,mutation

Insertional mutation

See: insertion

 Intellectual property
rights

Patents, copyrights, and trademarks.
See also: patent

Interference

One crossover event inhibits the chances of another crossover
event. Also known as positive interference. Negative interference
increases the chance of a second crossover.
See also: crossing
over

Interphase

The period in the cell cycle when DNA is replicated in the
nucleus; followed by mitosis.

 Intron

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.
See also: exon

 Isoenzyme

An enzyme performing the same function as another enzyme but
having a different set of amino acids. The two enzymes may function
at different speeds. 

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J

 Junk DNA

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. 

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K

 Karyotype

A photomicrograph of an individual's chromosomes arranged in a
standard format showing the number, size, and shape of each
chromosome type; used in low-resolution physical mapping to
correlate gross chromosomal abnormalities with the characteristics
of specific diseases.

 Kilobase (kb)

Unit of length for DNA fragments equal to 1000
nucleotides.

 Knockout

Deactivation of specific genes; used in laboratory organisms to
study gene function.
See also: gene,locus,model organisms

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L

 Library

An unordered collection of clones (i.e., cloned DNA from a
particular organism) whose relationship to each other can be
established by physical mapping.
See also: genomic library,arrayed library

 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.

Linkage disequilibrium

Where alleles occur together more often than can be accounted
for by chance. Indicates that the two alleles are physically close
on the DNA strand.
See also: Mendelian inheritance

 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).

 Localize

Determination of the original position (locus) of a gene or
other marker on a chromosome.

 Locus (pl.
loci)

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.
See also: gene
expression

 Long-Range Restriction
Mapping

Restriction enzymes are proteins that cut DNA at precise
locations. Restriction maps depict the chromosomal positions of
restriction-enzyme cutting sites. These are used as biochemical
"signposts," or markers of specific areas along the chromosomes.
The map will detail the positions where the DNA molecule is cut by
particular restriction enzymes. 

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M

Macrorestriction map

Map depicting the order of and distance between sites at which
restriction enzymes cleave chromosomes.

 Mapping

See: gene
mapping,linkage
map,physical
map

Mapping population

The group of related organisms used in constructing a genetic
map.

 Marker

See: genetic
marker

 Mass
spectrometry

An instrument used to identify chemicals in a substance by
their mass and charge.

 Megabase (Mb)

Unit of length for DNA fragments equal to 1 million nucleotides
and roughly equal to 1 cM.
See also: centimorgan

 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.
See also: mitosis

Mendelian inheritance

One method in which genetic traits are passed from parents to
offspring. Named for Gregor Mendel, who first studied and
recognized the existence of genes and this method of
inheritance.
See also: autosomal dominant,recessive gene,sex-linked

 Messenger
RNA (mRNA)

RNA that serves as a template for protein synthesis.
See also: genetic
code

 Metaphase

A stage in mitosis or meiosis during which the chromosomes are
aligned along the equatorial plane of the cell.

Microarray

Sets of miniaturized chemical reaction areas that may also be
used to test DNA fragments, antibodies, or proteins.

Microbial genetics

The study of genes and gene function in bacteria, archaea, and
other microorganisms. Often used in research in the fields of
bioremediation, alternative energy, and disease prevention.
See also: model
organisms,biotechnology,bioremediation

Microinjection

A technique for introducing a solution of DNA into a cell using
a fine microcapillary pipet.

Micronuclei

Chromosome fragments that are not incorporated into the nucleus
at cell division.

Mitochondrial DNA

The genetic material found in mitochondria, the organelles that
generate energy for the cell. Not inherited in the same fashion as
nucleic DNA.
See also: cell,DNA,genome,nucleus

 Mitosis

The process of nuclear division in cells that produces daughter
cells that are genetically identical to each other and to the
parent cell.
See also: meiosis

 Model
organisms

A laboratory animal or other organism useful for research.

 Modeling

The use of statistical analysis, computer analysis, or model
organisms to predict outcomes of research.

Molecular biology

The study of the structure, function, and makeup of
biologically important molecules.

Molecular farming

The development of transgenic animals to produce human proteins
for medical use.

Molecular genetics

The study of macromolecules important in biological
inheritance.

Molecular medicine

The treatment of injury or disease at the molecular level.
Examples include the use of DNA-based diagnostic tests or medicine
derived from DNA sequence information.

Monogenic disorder

A disorder caused by mutation of a single gene.
See also: mutation,polygenic disorder

Monogenic inheritance

See: monogenic disorder

 Monosomy

Possessing only one copy of a particular chromosome instead of
the normal two copies.
See also: cell,chromosome,gene expression,trisomy

 Morbid map

A diagram showing the chromosomal location of genes associated
with disease.

 Mouse
model

See: model
organisms

 Multifactorial or
multigenic disorder

See: polygenic disorder

Multiplexing

A laboratory approach that performs multiple sets of reactions
in parallel (simultaneously); greatly increasing speed and
throughput.

 Murine

Organism in the genus Mus. A rat or mouse.

 Mutagen

An agent that causes a permanent genetic change in a cell. Does
not include changes occurring during normal genetic
recombination.

Mutagenicity

The capacity of a chemical or physical agent to cause permanent
genetic alterations.
See also: somatic cell genetic mutation

 Mutation

Any heritable change in DNA sequence.
See also: polymorphism

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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).
See also: DNA

 Northern
blot

A gel-based laboratory procedure that locates mRNA sequences on
a gel that are complementary to a piece of DNA used as a
probe.
See also: DNA,library

 Nuclear
transfer

A laboratory procedure in which a cell's nucleus is removed and
placed into an oocyte with its own nucleus removed so the genetic
information from the donor nucleus controls the resulting cell.
Such cells can be induced to form embryos. This process was used to
create the cloned sheep "Dolly".
See also: cloning

 Nucleic
acid

A large molecule composed of nucleotide subunits.
See also: DNA

 Nucleolar organizing
region

A part of the chromosome containing rRNA genes.

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.
See also: DNA,base pair,RNA

 Nucleus

The cellular organelle in eukaryotes that contains most of the
genetic material. 

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O

 Oligo

See: oligonucleotide

Oligogenic

A phenotypic trait produced by two or more genes working
together.
See also: polygenic disorder

Oligonucleotide

A molecule usually composed of 25 or fewer nucleotides; used as
a DNA synthesis primer.
See also: nucleotide

 Oncogene

A gene, one or more forms of which is associated with cancer.
Many oncogenes are involved, directly or indirectly, in controlling
the rate of cell growth.

 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).

 Operon

A set of genes transcribed under the control of an operator
gene.

Overlapping clones

See: genomic
library

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P

 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.
Based on bacteriophage (a virus) P1 genome.
See also: cloning
vector

 Patent

In genetics, conferring the right or title to genes, gene
variations, or identifiable portions of sequenced genetic material
to an individual or organization.
See also: gene

 Pedigree

A family tree diagram that shows how a particular genetic trait
or disease has been inherited.
See also: inherit

Penetrance

The probability of a gene or genetic trait being expressed.
"Complete" penetrance means the gene or genes for a trait are
expressed in all the population who have the genes. "Incomplete"
penetrance means the genetic trait is expressed in only part of the
population. The percent penetrance also may change with the age
range of the population.

 Peptide

Two or more amino acids joined by a bond called a "peptide
bond."
See also: polypeptide

 Phage

A virus for which the natural host is a bacterial cell.

Pharmacogenomics

The study of the interaction of an individual's genetic makeup
and response to a drug.

 Phenocopy

A trait not caused by inheritance of a gene but appears to be
identical to a genetic trait.

 Phenotype

The physical characteristics of an organism or the presence of
a disease that may or may not be genetic.
See also: genotype

 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.

 Plasmid

Autonomously replicating extra-chromosomal circular DNA
molecules, distinct from the normal bacterial genome and
nonessential for cell survival under nonselective conditions. Some
plasmids are capable of integrating into the host genome. A number
of artificially constructed plasmids are used as cloning
vectors.

Pleiotropy

One gene that causes many different physical traits such as
multiple disease symptoms.

Pluripotency

The potential of a cell to develop into more than one type of
mature cell, depending on environment.

Polygenic disorder

Genetic disorder resulting from the combined action of alleles
of more than one gene (e.g., heart disease, diabetes, and some
cancers). Although such disorders are inherited, they depend on the
simultaneous presence of several alleles; thus the hereditary
patterns usually are more complex than those of single-gene
disorders.
See also: single-gene disorder

 Polymerase chain
reaction (PCR)

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.

Polymerase, DNA or RNA

Enzyme that catalyzes the synthesis of nucleic acids on
preexisting nucleic acid templates, assembling RNA from
ribonucleotides or DNA from deoxyribonucleotides.

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.
See also: mutation

Polypeptide

A protein or part of a protein made of a chain of amino acids
joined by a peptide bond.

Population genetics

The study of variation in genes among a group of
individuals.

Positional cloning

A technique used to identify genes, usually those that are
associated with diseases, based on their location on a
chromosome.

 Premature chromosome
condensation (PCC)

A method of studying chromosomes in the interphase stage of the
cell cycle.

 Primer

Short preexisting polynucleotide chain to which new
deoxyribonucleotides can be added by DNA polymerase.

 Privacy

In genetics, the right of people to restrict access to their
genetic information.

 Probe

Single-stranded DNA or RNA molecules of specific base sequence,
labeled either radioactively or immunologically, that are used to
detect the complementary base sequence by hybridization.

Prokaryote

Cell or organism lacking a membrane-bound, structurally
discrete nucleus and other subcellular compartments. Bacteria are
examples of prokaryotes.
See also: chromosome,eukaryote

 Promoter

A DNA site to which RNA polymerase will bind and initiate
transcription.

Pronucleus

The nucleus of a sperm or egg prior to fertilization.
See also: nucleus,transgenic

 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.

 Proteome

Proteins expressed by a cell or organ at a particular time and
under specific conditions.

Proteomics

The study of the full set of proteins encoded by a genome.

Pseudogene

A sequence of DNA similar to a gene but nonfunctional; probably
the remnant of a once-functional gene that accumulated
mutations.

 Purine

A nitrogen-containing, double-ring, basic compound that occurs
in nucleic acids. The purines in DNA and RNA are adenine and
guanine.
See also: base
pair

Pyrimidine

A nitrogen-containing, single-ring, basic compound that occurs
in nucleic acids. The pyrimidines in DNA are cytosine and thymine;
in RNA, cytosine and uracil.
See also: base
pair

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R

Radiation hybrid

A hybrid cell containing small fragments of irradiated human
chromosomes. Maps of irradiation sites on chromosomes for the
human, rat, mouse, and other genomes provide important markers,
allowing the construction of very precise STS maps indispensable to
studying multifactorial diseases.
See also: sequence tagged site

Rare-cutter enzyme

See: restriction-enzyme cutting site

 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.

 Reciprocal
translocation

When a pair of chromosomes exchange exactly the same length and
area of DNA. Results in a shuffling of genes.

Recombinant clone

Clone containing recombinant DNA molecules.
See also: recombinant DNA technology

 Recombinant DNA
molecules

A combination of DNA molecules of different origin that are
joined using recombinant DNA technologies.

 Recombinant DNA
technology

Procedure used to join together DNA segments in a cell-free
system (an environment outside a cell or organism). Under
appropriate conditions, a recombinant DNA molecule can enter a cell
and replicate there, either autonomously or after it has become
integrated into a cellular chromosome.

Recombination

The process by which progeny derive a combination of genes
different from that of either parent. In higher organisms, this can
occur by crossing over.
See also: crossing
over,mutation

 Regulatory region or
sequence

A DNA base sequence that controls gene expression.

 Repetitive
DNA

Sequences of varying lengths that occur in multiple copies in
the genome; it represents much of the human genome.

 Reporter
gene

See: marker

Resolution

Degree of molecular detail on a physical map of DNA, ranging
from low to high.

 Restriction enzyme,
endonuclease

A protein that recognizes specific, short nucleotide sequences
and cuts DNA at those sites. Bacteria contain over 400 such enzymes
that recognize and cut more than 100 different DNA sequences.
See also: restriction enzyme cutting site

 Restriction
fragment length polymorphism (RFLP)

Variation between individuals in DNA fragment sizes cut by
specific restriction enzymes; polymorphic sequences that result in
RFLPs are used as markers on both physical maps and genetic linkage
maps. RFLPs usually are caused by mutation at a cutting site.
See also: marker,polymorphism

 Restriction-enzyme
cutting site

A specific nucleotide sequence of DNA at which a particular
restriction enzyme cuts the DNA. Some sites occur frequently in DNA
(e.g., every several hundred base pairs); others much less
frequently (rare-cutter; e.g., every 10,000 base pairs).

Retroviral infection

The presence of retroviral vectors, such as some viruses, which
use their recombinant DNA to insert their genetic material into the
chromosomes of the host's cells. The virus is then propogated by
the host cell.

Reverse transcriptase

An enzyme used by retroviruses to form a complementary DNA
sequence (cDNA) from their RNA. The resulting DNA is then inserted
into the chromosome of the host cell.

Ribonucleotide

See: nucleotide

 Ribose

The five-carbon sugar that serves as a component of RNA.
See also: ribonucleic acid,deoxyribose

 Ribosomal
RNA (rRNA)

A class of RNA found in the ribosomes of cells.

 Ribosomes

Small cellular components composed of specialized ribosomal RNA
and protein; site of protein synthesis.
See also: RNA

 Risk
communication

In genetics, a process in which a genetic counselor or other
medical professional interprets genetic test results and advises
patients of the consequences for them and their offspring.

 RNA (Ribonucleic acid)

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. 

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S

 Sanger
sequencing

A widely used method of determining the order of bases in
DNA.
See also: sequencing,shotgun sequencing

 Satellite

A chromosomal segment that branches off from the rest of the
chromosome but is still connected by a thin filament or stalk.

 Scaffold

In genomic mapping, a series of contigs that are in the right
order but not necessarily connected in one continuous stretch of
sequence.

Segregation

The normal biological process whereby the two pieces of a
chromosome pair are separated during meiosis and randomly
distributed to the germ cells.

 Sequence

See: base
sequence

Sequence assembly

A process whereby the order of multiple sequenced DNA fragments
is determined.

Sequence tagged site (STS)

Short (200 to 500 base pairs) DNA sequence that has a single
occurrence in the human genome and whose location and base sequence
are known. Detectable by polymerase chain reaction, STSs are useful
for localizing and orienting the mapping and sequence data reported
from many different laboratories and serve as landmarks on the
developing physical map of the human genome. Expressed sequence
tags (ESTs) are STSs derived from cDNAs.

Sequencing

Determination of the order of nucleotides (base sequences) in a
DNA or RNA molecule or the order of amino acids in a protein.

Sequencing technology

The instrumentation and procedures used to determine the order
of nucleotides in DNA.

 Sex
chromosome

The X or Y chromosome in human beings that determines the sex
of an individual. Females have two X chromosomes in diploid cells;
males have an X and a Y chromosome. The sex chromosomes comprise
the 23rd chromosome pair in a karyotype.
See also: autosome

Sex-linked

Traits or diseases associated with the X or Y chromosome;
generally seen in males.
See also: gene,mutation,sex chromosome

 Shotgun
method

Sequencing method that involves randomly sequenced cloned
pieces of the genome, with no foreknowledge of where the piece
originally came from. This can be contrasted with "directed"
strategies, in which pieces of DNA from known chromosomal locations
are sequenced. Because there are advantages to both strategies,
researchers use both random (or shotgun) and directed strategies in
combination to sequence the human genome.
See also: library,genomic library

 Single nucleotide
polymorphism (SNP)

DNA sequence variations that occur when a single nucleotide (A,
T, C, or G) in the genome sequence is altered.
See also: mutation,polymorphism,single-gene
disorder

Single-gene disorder

Hereditary disorder caused by a mutant allele of a single gene
(e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell
disease).
See also: polygenic disorders

 Somatic
cell

Any cell in the body except gametes and their precursors.
See also: gamete

 Somatic cell gene
therapy

Incorporating new genetic material into cells for therapeutic
purposes. The new genetic material cannot be passed to
offspring.
See also: gene
therapy

 Somatic cell genetic
mutation

A change in the genetic structure that is neither inherited nor
passed to offspring. Also called acquired mutations.
See also: germ line genetic mutation

Southern blotting

Transfer by absorption of DNA fragments separated in
electrophoretic gels to membrane filters for detection of specific
base sequences by radio-labeled complementary probes.

Spectral karyotype (SKY)

A graphic of all an organism's chromosomes, each labeled with a
different color. Useful for identifying chromosomal
abnormalities.
See also: chromosome

 Splice
site

Location in the DNA sequence where RNA removes the noncoding
areas to form a continuous gene transcript for translation into a
protein.

 Sporadic
cancer

Cancer that occurs randomly and is not inherited from parents.
Caused by DNA changes in one cell that grows and divides, spreading
throughout the body.
See also: hereditary cancer

 Stem cell

Undifferentiated, primitive cells in the bone marrow that have
the ability both to multiply and to differentiate into specific
blood cells.

Structural genomics

The effort to determine the 3D structures of large numbers of
proteins using both experimental techniques and computer
simulation

Substitution

In genetics, a type of mutation due to replacement of one
nucleotide in a DNA sequence by another nucleotide or replacement
of one amino acid in a protein by another amino acid.
See also: mutation

 Suppressor
gene

A gene that can suppress the action of another gene.

 Syndrome

The group or recognizable pattern of symptoms or abnormalities
that indicate a particular trait or disease.

 Syngeneic

Genetically identical members of the same species.

 Synteny

Genes occurring in the same order on chromosomes of different
species.
See also: linkage,conserved sequence

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T

Tandem repeat sequences

Multiple copies of the same base sequence on a chromosome; used
as markers in physical mapping.
See also: physical
map

Targeted mutagenesis

Deliberate change in the genetic structure directed at a
specific site on the chromosome. Used in research to determine the
targeted region's function.
See also: mutation,polymorphism

Technology transfer

The process of transferring scientific findings from research
laboratories to the commercial sector.

Telomerase

The enzyme that directs the replication of telomeres.

 Telomere

The end of a chromosome. This specialized structure is involved
in the replication and stability of linear DNA molecules.
See also: DNA
replication

Teratogenic

Substances such as chemicals or radiation that cause abnormal
development of a embryo.
See also: mutatgen

 Thymine (T)

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

Toxicogenomics

The study of how genomes respond to environmental stressors or
toxicants. Combines genome-wide mRNA expression profiling with
protein expression patterns using bioinformatics to understand the
role of gene-environment interactions in disease and
dysfunction.

Transcription

The synthesis of an RNA copy from a sequence of DNA (a gene);
the first step in gene expression.
See also: translation

Transcription factor

A protein that binds to regulatory regions and helps control
gene expression.

Transcriptome

The full complement of activated genes, mRNAs, or transcripts
in a particular tissue at a particular time

Transfection

The introduction of foreign DNA into a host cell.
See also: cloning
vector,gene
therapy

 Transfer RNA
(tRNA)

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.

Transformation

A process by which the genetic material carried by an
individual cell is altered by incorporation of exogenous DNA into
its genome.

Transgenic

An experimentally produced organism in which DNA has been
artificially introduced and incorporated into the organism's germ
line.
See also: cell,DNA,gene,nucleus,germ line

Translation

The process in which the genetic code carried by mRNA directs
the synthesis of proteins from amino acids.
See also: transcription

Translocation

A mutation in which a large segment of one chromosome breaks
off and attaches to another chromosome.
See also: mutation

Transposable element

A class of DNA sequences that can move from one chromosomal
site to another.

 Trisomy

Possessing three copies of a particular chromosome instead of
the normal two copies.
See also: cell,gene,gene expression,chromosome

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U

 Uracil

A nitrogenous base normally found in RNA but not DNA; uracil is
capable of forming a base pair with adenine.
See also: base
pair,nucleotide

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V

 Vector

See: cloning
vector

 Virus

A noncellular biological entity that can reproduce only within
a host cell. Viruses consist of nucleic acid covered by protein;
some animal viruses are also surrounded by membrane. Inside the
infected cell, the virus uses the synthetic capability of the host
to produce progeny virus.
See also: cloning
vector

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W

 Western
blot

A technique used to identify and locate proteins based on their
ability to bind to specific antibodies.
See also: DNA,Northern blot,protein,RNA,Southern blotting

 Wild type

The form of an organism that occurs most frequently in
nature.

 Working Draft DNA
Sequence

See: Draft
DNA Sequence

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X

 X
chromosome

One of the two sex chromosomes, X and Y.
See also: Y
chromosome,sex
chromosome

 Xenograft

Tissue or organs from an individual of one species transplanted
into or grafted onto an organism of another species, genus, or
family. A common example is the use of pig heart valves in humans. 

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Y

 Y
chromosome

One of the two sex chromosomes, X and Y.
See also: X
chromosome,sex
chromosome

 Yeast artificial
chromosome (YAC)

Constructed from yeast DNA, it is a vector used to clone large
DNA fragments.
See also: cloning
vector,cosmid

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Z

Zinc-finger protein

A secondary feature of some proteins containing a zinc atom; a
DNA-binding protein. 

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Updated 15-Apr-03 

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 The online presentation of this publication is a special
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