Alternative form of a genetic locus; a
single allele for each locus is inherited
separately from each parent (e.g., at a
locus for eye color the allele might result
in blue or brown eyes).
increase in the number of copies of a
specific DNA fragment; can be in vivo or in
Base sequence: The
order of nucleotide bases in a DNA molecule.
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
An exact copy made of biological material
such as a DNA segment (a gene or other
region), a whole cell, or a complete
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.
The relative order of base pairs, whether in
a fragment of DNA, a gene, a chromosome, or
an entire genome.
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.
Separation is based on these differences.
Use of flow cytometry to analyze and
separate chromosomes on the basis of their
a DNA separation technique that is very
important in DNA sequencing. Standard
sequencing procedures involve cloning DNA
fragments into special sequencing cloning
vectors that carry tiny pieces of DNA. The
next step is to determine the base sequence
of the tiny fragments by a special procedure
that generates a series of even tinier DNA
fragments that differ in size by only one
base. These nested fragments are separated
by gel electrophoresis, in which the DNA
pieces are added to a gelatinous solution,
allowing the fragments to work their way
down through the gel. Smaller pieces move
faster and will reach the bottom first.
Movement through the gel is hastened by
applying an electrical field to the gel.
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 gene
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).
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.
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
The sequence of nucleotides, coded in
triplets (codons) along the mRNA, that
determines the sequence of amino acids in
protein synthesis. The DNA sequence of a
gene can be used to predict the mRNA
sequence, and the genetic code can in turn
be used to predict the amino acid sequence.
The study of the patterns of inheritance of
All the genetic material in the chromosomes
of a particular organism; its size is
generally given as its total number of base
Research and technology development effort
aimed at mapping and sequencing some or all
of the genome of human beings and other
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
The presence of different alleles at one or
more loci on homologous chromosomes
Chromosome containing the same linear gene
sequences as another, each derived from one
Insertion of normal DNA directly into cells
to correct a genetic defect.
Collective name for several projects begun
in 1986 by Department of Energy to (1)
create an ordered set of DNA segments from
known chromosomal locations, (2) develop new
computational methods for analyzing genetic
map and DNA sequence data, and (3) develop
new techniques and instruments for detecting
and analyzing DNA. This DOE initiative is
now known as the Human Genome Program. The
national effort, led by DOE and NIH, is
known as the Human Genome Project.
The process of joining two complementary
strands of DNA or one each of DNA and RNA to
form a double-stranded molecule.
The study of the application of computer and
statistical techniques to the management of
information. In genome projects, informatics
includes the development of methods to
search databases quickly, to analyze DNA
sequence information and to predict protein
sequence and structure from DNA sequence
Use of a DNA or RNA probe to detect the
presence of the complementary DNA sequence
in cloned cells.
Outside a living organism. For example,
tests done in vitro often means they are
done in the test tube.
In a living organism. For example, tests
done in vivo usually means they are done in
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.
The proximity of two or more markers (e.g.,
genes) on a chromosome; the closer together
the markers are, the lower the probability
that they will be separated during DNA
repair or replication processes and hence
the greater the probability that they will
be inherited together.
A map of the relative positions of genetic
loci on a chromosome, determined on the
basis of how often the loci are inherited
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 regions of DNA that are
RNA that serves as a template for protein
Any heritable change in DNA sequence.
A large molecule composed of 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
The cellular organelle that contains the
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.
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 are usually more complex
than those of single gene disorders.
chain reaction (PCR):
A method for amplifying a DNA base sequence
using a heat-stable enzyme known as
polymerase and two 20-base primers, one
complementary to the (+) strand at one end
of the sequence to be amplified and the
other 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.
Difference in DNA sequence among
individuals. Genetic variations occurring in
more than 1% of a population would be
considered useful polymorphisms for genetic
a technique used to identify genes, usually
those that are associated with diseases,
based on their location on a chromosome.
This id in contrast to the older,
"functional cloning" technique
that relies on some knowledge of a gene's
protein product. For most diseases,
researchers have no such knowledge.
Short preexisting polynucleotide chain to
which new deoxyribonucleotides can be added
by DNA polymerase.
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.
A site on DNA to which RNA polymerase will
bind and initiate transcription. The study
of the patterns of inheritance of specific
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 coding 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.
A combination of DNA molecules of different
origin that are joined using recombinant DNA
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
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.
region or sequence:
A DNA base sequence that controls gene
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
Small cellular components composed of
specialized ribosomal RNA and protein; site
of protein synthesis.
Determination of the order of nucleotides
(base sequences) in a DNA or RNA molecule or
the order of amino acids in a protein.
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.
Hereditary disorder caused by a mutant
allele of a single gene (e.g., Duchenne
muscular dystrophy, retinoblastoma, sickle
Any cell in the body except gametes and
The synthesis of an RNA copy from a sequence
of DNA (a gene); the first step in gene
A nitrogenous base normally found in RNA but
not DNA; uracil is capable of forming a base
pair with adenine.
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.
artificial chromosome (YAC):
A vector used to clone DNA fragments (up to
400 kb); it is constructed from the
telomeric, centromeric, and replication
origin sequences needed for replication in
yeast cells. Compare cloning vector.
A fertilized egg.