Glossary of Genetic Terms
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- Achondroplasia -- the most common
and well known form of short limbed dwarfism characterized by a normal trunk size with
disproportionally short arms and legs, and a disproportionally large head; autosomal
- Advanced maternal age -- women over age 34 (age 35
at delivery) at increased risk for nondisjunction trisomy in fetus.
- Alcoholism -- a chronic and progressive condition
characterized by the inability to control the consumption of alcohol.
- Allele -- an alternative form of a gene; any one of
several mutational forms of a gene.
- Alpha-fetoprotein (AFP) -- a protein excreted by the
fetus into the amniotic fluid and from there into the mother's bloodstream through the
- Alu repetitive sequence -- the most common dispersed
repeated DNA sequence in the human genome accounting for 5% of human DNA. The name is
derived from the fact that these sequences are cleaved by the restriction endonuclease
- Amino acid sequence -- the linear order of the amino
acids in a protein or peptide.
- Amniocentesis -- prenatal diagnosis method using
cells in the amniotic fluid to determine the number and kind of chromosomes of the fetus
and, when indicated, perform biochemical studies.
- Amniocyte -- cells obtained by amniocentesis.
- Amplification -- any process by which specific DNA
sequences are replicated disproportionately greater than their representation in the
- Aneuploidy -- state of having variant chromosome
number (too many or too few). (i.e. Down syndrome, Turner syndrome).
- Angelman syndrome -- a condition characterized by
severe mental deficiency, developmental delay and growth deficiency, puppet-like gait and
frequent laughter unconnected to emotions of happiness.
- Apert syndrome -- a condition caused by the
premature closure of the sutures of the skull bones, resulting in an altered head shape,
with webbed fingers and toes. Autosomal dominant.
- Artificial insemination -- the placement of sperm
into a female reproductive tract or the mixing of male and female gametes by other than
- Autosome -- a nuclear chromosome other than the X-
- Autoradiograph -- a photographic picture showing the
position of radioactive substances in tissues.
- Bacteriophage -- a virus whose host
is a bacterium; commonly called phage.
- Barr body -- the condensed single X-chromosome seen
in the nuclei of somatic cells of female mammals. base pair a pair of hydrogen-bonded
nitrogenous bases (one purine and one pyrimidine) that join the component strands of the
DNA double helix.
- Base sequence -- a partnership of organic bases
found in DNA and RNA; adenine forms a base pair with thymine (or uracil) and guanine with
cytosine in a double-stranded nucleic acid molecule.
- Baysian analysis -- a mathematical method to further
refine recurrence risk taking into account other known factors.
- Becker muscular dystrophy -- X-linked condition
characterized by progressive muscle weakness and wasting; manifests later in life with
progression less severe than Duchenne muscular dystrophy.
- Carrier -- an individual
heterozygous for a single recessive gene.
- cDNA -- complementary DNA produced from a RNA
template by the action of RNA- dependent DNA polymerase.
- Centromere -- a region of a chromosome to which
spindle traction fibers attach during mitosis and meiosis; the position of the centromere
determines whether the chromosome is considered an acrocentric, metacentric or telomeric
- Charcot-Marie Tooth disease -- a condition
characterized by degeneration of the motor and sensory nerves that control movement and
feeling in the arm below the elbow and the leg below the knee; transmitted in autosomal
dominant, autosomal recessive and X-linked forms.
- Chorionic villus sampling -- an invasive prenatal
diagnostic procedure involving removal of villi from the human chorion to obtain
chromosomes and cell products for diagnosis of disorders in the human embryo.
- Chromosome -- in the eukaryotic nucleus, one of the
threadlike structures consisting of chromatin and carry genetic information arranged in a
- Chromosome banding -- a technique for staining
chromosomes so that bands appear in a unique pattern particular to the chromosome.
- Cleft lip/palate -- congenital condition with cleft
lip alone, or with cleft palate; cause is thought to be multifactorial.
- Clone -- genetically engineered replicas of DNA
- Cloned DNA -- any DNA fragment that passively
replicates in the host organism after it has been joined to a cloning vector.
- Codon -- a sequence of three nucleotides in mRNA
that specifies an amino acid.
- Consanguinity -- genetic relationship.
Consanguineous individuals have at least one common ancestor in the preceding few
- Conservative change -- an amino acid change that
does not affect significantly the function of the protein.
- Contiguous genes -- genes physically close on a
chromosome that when acting together express a phenotype.
- Cosmids -- plasmid vectors designed for cloning
large fragments of eukaryotic DNA; the vector is a plasmid into which phage lambda
cohesive end sites have been inserted.
- CpG islands -- areas of multiple CG repeats in DNA.
- Cri-du-chat syndrome -- a chromosomal condition
(monosomy 5p). Name comes from the distinctive mewing cry of affected infants;
characterized by significant mental deficiency, low birthweight, failure to thrive and
short stature; deletion of a small section of the short arm of chromosome 5.
- Crossovers -- the exchange of genetic material
between two paired chromosome during meiosis.
- Cornelia de Lange syndrome -- condition involving
growth deficiency, significant developmental delay, anomalies of the extremities and a
characteristic facial appearance.
- Cytogenetics -- the study of chromosomes.
- Cystic fibrosis -- an autosomal recessive genetic
condition of the exocrine glands, which causes the body to produce excessively thick,
sticky mucus that clogs the lungs and pancreas, interfering with breathing and digestion.
- Degenerate codon -- a codon that
specifies the same amino acid as another codon.
- Deletion -- the loss of a segment of the genetic
material from a chromosome.
- Deletion mapping -- the use of overlapping deletions
to localize the position of an unknown gene on a chromosome or linkage map.
- Disease -- any deviation from the normal structure
or function of any part, organ, or system of the body that is manifested by a
characteristic set of symptoms and signs whose pathology and prognosis may be known or
- DMD -- Duchenne muscular dystrophy.
- DNA fingerprint technique -- a method employed to
determine differences in amino acid sequences between related proteins; relies upon the
presence of a simple tandem-repetitive sequences that are scattered throughout the human
- DNA hybridization -- a technique for selectively
binding specific segments of single-stranded (ss) DNA or RNA by base pairing to
complementary sequences on ssDNA molecules that are trapped on a nitrocellulose filter.
- DNA probe -- any biochemical used to identify or
isolate a gene, a gene product, or a protein.
- DNA sequencing -- "plus and minus" or
"primed synthesis" method, developed by Sanger, DNA is synthesized in vitro in
such a way that it is radioactively labeled and the reaction terminates specifically at
the position corresponding to a given base; the "chemical" method, ssDNA is
subjected to several chemical cleavage protocols that selectively make breaks on one side
of a particular base.
- DOE -- Department of Energy.
- Dominant -- alleles that determine the phenotype
displayed in a heterozygote with another (recessive) allele.
- Down syndrome -- a type of mental deficiency due to
trisomy (three copies) of autosome 21, a translocation of 21 or mosaicism.
- Duchenne/Becker muscular dystrophy -- the most
common and severe form of muscular dystrophy; transmitted as an X-linked trait. X-linked
recessive. Symptoms include onset at 2-5 years with difficulty with gait and stairs,
enlarged calf muscles, progression to wheelchair by adolescence, shortened life span.
- Dystonia -- neurologic condition involving repeated
twisting and movement. Involves a variety of muscle groups. Intelligence not effected.
Three forms: childhood - autosomal dominant, autosomal recessive, adult-acquired.
- Dwarfism -- conditions of short stature with adult
height under 4'10" as adult, usually with normal intelligence and lifespan. Ehlers
Danlos Syndrome connective tissue condition including problems with tendons, ligaments,
skin, bones, cartilage, and membranes surrounding blood vessels and nerves. Symptoms
include joint laxity, elastic skin, dislocations. Many forms: autosomal dominant,
autosomal recessive, X-linked forms.
- ELSI -- ethical, legal and social
implications (of HGP).
- Endonuclease -- an enzyme that breaks the internal
phosphodiester bonds in a DNA molecule.
- Ethics -- the study of fundamental principles which
defines values and determines moral duty and obligation.
- Erythrocytes -- the hemoglobin-containing cell found
in the blood of vertebrates.
- Euchromatin -- the chromatin that shows the staining
behavior characteristic of the majority of the chromosomal complement.
- Eugenics -- the improvement of humanity by altering
its genetic composition by encouraging breeding of those presumed to have desirable genes.
- Exons -- portion of a gene included in the
transcript of a gene and survives processing of the RNA in the cell nucleus to become part
of a spliced messenger of a structural RNA in the cell cytoplasm; an exon specifies the
amino acid sequence of a portion of the complete polypeptide.
- Fetal alcohol syndrome -- a link
between excessive alcohol consumption during pregnancy and birth defects; characteristics
include small head and eyes, folds of the skin that obscure the inner juncture of the
eyelids, short, upturned nose, and thin lips.
- FISH -- florescent in situ hybridization: a
technique for uniquely identifying whole chromosomes or parts of chromosomes using
florescent tagged DNA.
- 5' - end -- the end of a polynucleotide with a free
(or phosphorylated or capped) 5' - hydroxyl group; transcription/translation begins at
- Fragile sites -- a non-staining gap of variable
width that usually involves both chromatids and is always at exactly the same point on a
specific chromosome derived from an individual or kindred.
- Fragile-X syndrome -- X-linked trait; the second
most common identifiable cause of genetic mental deficiency.
- Gamete -- an haploid cell.gel
electrophoresis the process by which nucleic acids (DNA or RNA) or proteins are separated
by size according to movement of the charged molecules in an electrical field.
- Gene -- a hereditary unit that occupies a certain
position on a chromosome; a unit that has one or more specific effects on the phenotype,
and can mutate to various allelic forms.
- Gene amplification -- any process by which specific
DNA sequences are replicated disproportionately greater than their representation in the
parent molecules; during development, some genes become amplified in specific tissues.
- Gene map -- the linear arrangement of mutable sites
on a chromosome as deduced from genetic recombination experiments.
- Gene therapy -- addition of a functional gene or
group of genes to a cell by gene insertion to correct an hereditary disease.
- Genetic counseling -- the educational process that
helps individuals, couples, or families to understand genetic information and issues that
may have an impact on them.
- Genetic linkage map -- a chromosome map showing the
relative positions of the known genes on the chromosomes of a given species.
- Genetic screening -- testing groups of individuals
to identify defective genes capable of causing hereditary conditions.
- Genetic variation -- a phenotypic variance of a
trait in a population attributed to genetic heterogeneity.
- Genome -- all of the genes carried by a single
gamete; the DNA content of an individual, which includes all 44 autosomes, 2 sex
chromosomes, and the mitochondrial DNA.
- Genotype -- genetic constitution of an organism.
- Germ cell -- a sex cell or gamete (egg or
spermatozoan).Haldane equation Haldane's law: the generalization that if first generation
hybrids are produced between two species, but one sex is absent, rare, or sterile, that
sex is the heterogamic sex.
- Hardy-Weinberg Law -- the concept
that both gene frequencies and genotype frequencies will remain constant from generation
to generation in an infinitely large, interbreeding population in which mating is at
random and there is no selection, migration or mutation.
- Heterozygote -- having two alleles that are
different for a given gene.
- Hemophilia -- a sex-linked disease in humans in
which the blood-clotting process is defective.
- Heterogeneity -- the production of identical or
similar phenotypes by different genetic mechanisms.
- HGP -- Human Genome Project.
- HHMI -- Howard Hughes Medical Institute.
- Homologous chromosomes -- chromosomes that pair
during meiosis; each homologue is a duplicate of one chromosome from each parent.
- Homozygote -- having identical alleles at one or
more loci in homologous chromosome segments.
- Housekeeping genes -- those genes expressed in all
cells because they provide functions needed for sustenance of all cell types.
- HUGO -- Human Genome Organization.
- Huntington disease -- a disease characterized by
irregular, spasmodic involuntary movements of the limbs and facial muscles, mental
deterioration and death, usually within 20 years of the onset of symptoms.
- Hybridization -- the pairing of a single-stranded,
labeled probe (usually DNA) to its complementary sequence.
- Ichthyosis -- any of several
hereditary or congenital skin conditions; skin of affected individuals has a dry, scaly
- Imprinting -- a chemical modification of a gene
allele which can be used to identify maternal or paternal origin of chromosome.
- Incomplete penetrance -- the gene for a condition is
present, but not obviously expressed in all individuals in a family with the gene.
- In situ hybridization -- hybridization of a labeled
probe to its complementary sequence within intact, banded chromosomes.
- Introns -- a segment of DNA (between exons) that is
transcribed into nuclear RNA, but are removed in the subsequent processing into mRNA.
- Isochromosome -- a metacentric chromosome produced
during mitosis or meiosis when the centromere splits transversely instead of
longitudinally; the arms of such chromosome are equal in length and genetically identical,
however, the loci are positioned in reverse sequence in the two arms.
- Klinefelter syndrome -- an endocrine
condition caused by a an extra X-chromosome (47,XXY); characterized by the lack of normal
sexual development and testosterone, leading to infertility and adjustment problems if not
detected and treated early.
- Karyotype -- a set of photographed, banded
chromosomes arranged in order from largest to smallest.
- Lligase -- an enzyme that functions
in DNA repair.
- Linkage -- the greater association in inheritance of
two or more nonallelic genes than is to be expected from independent assortment; genes are
linked because they reside on the same chromosome.
- Linkage -- analysis of pedigree the tracking of a
gene through a family by following the inheritance of a (closely associated) gene or trait
and a DNA marker.
- Lod score -- logarithm of the odd score; a measure
of the likelihood of two loci being within a measurable distance of each other.
- Marfan syndrome -- autosomal
dominant condition of connective tissue; affects the skeletal, ocular and cardiovascular
- Marker -- a gene with a known location on a
chromosome and a clear-cut phenotype, used as a point of reference when mapping a new
- Meiosis -- the doubling of gametic chromosome
- Methylation -- addition of a methyl group (-CH3) to
DNA or RNA.
- Methylmalonic acidemia -- a group of conditions
characterized by the inability to metabolize methylmalonic acid or by a defect in the
metabolism of Vitamin B12.
- Missense mutation -- a change in the base sequence
of a gene that alters or eliminates a protein.
- Mitochondrial DNA -- the mitochondrial genome
consists of a circular DNA duplex, with 5 to 10 copies per organelle.
- Mitosis -- nuclear division.
- mRNA -- messenger RNA; an RNA molecular that
functions during translation to specify the sequence of amino acids in a nascent
- Multifactorial -- a characteristic influenced in its
expression by many factors, both genetic and environmental.
- Mutation -- process by which genes undergo a
- Myotonic dystrophy -- a combination of progressive
weakening of the muscles and muscle spasms or rigidity, with difficulty relaxing a
contracted muscle; inherited as an autosomal dominant trait.
- Neurofibromatosis -- one of the most
common single gene conditions affecting the human nervous system; in most cases,
"cafe au lait" spots, are the only symptom; inherited as an autosomal dominant
trait, with 50% being new mutations.
- NIH -- National Institutes of Health.
- Nonsense mutation -- a mutation in which a codon is
changed to a stop codon, resulting in a truncated protein product.
- Noonan syndrome -- a condition characterized by
short stature and ovarian or testicular dysfunction, mental deficiency, and lesions of the
- Northern analysis -- a technique for transferring
electrophoretically resolved RNA segments from an agarose gel to a nitrocellulose filter
paper sheet via capillary action.
- Nucleotide -- one of the monomeric units from which
DNA or RNA polymers are constructed; consists of a purine or pyrimidine base, a pentose
sugar and a phosphoric acid group.
- Oncogenes -- genes involved in cell
cycle control (growth factors, growth factor regulator genes, etc), a mutation can lead to
- Osteogenesis imperfecta -- a condition also known as
brittle bone disease; characterized by a triangular shaped face with yellowish brown
teeth, short stature and stunted growth, scoliosis, high pitched voice, excessive sweating
and loose joints.
- Parthenogenesis -- the development
of an individual from an egg without fertilization.
- PCR -- polymerase chain reaction; a technique for
copying the complementary strands of a target DNA molecule simultaneously for a series of
cycles until the desired amount is obtained.
- Pedigree -- a diagram of the heredity of a
particular trait through many generations of a family.
- Phenotype -- observable characteristics of an
organism produced by the organism's genotype interacting with the environment.
- Physical map -- map where the distance between
markers is the actual distance, such as the number of base pairs.
- PKU -- phenylketonuria, an enzyme deficiency
condition characterized by the inability to convert one amino acid, phenylalanine, to
another, tyrosine, resulting in mental deficiency. plasmid double-stranded, circular,
bacterial DNA into which a fragment of DNA from another organism can be inserted.
- Pleiotropy -- the phenomenon of variable phenotypes
for a number of distinct and seemingly unrelated phenotypic effects.
- Polycystic kidney disease (PKD) -- a group of
conditions characterized by fluid filled sacs that slowly develop in both kidneys,
eventually resulting in kidney malfunction.
- Polymerase -- any enzyme that catalyzes the
formation of DNA or RNA from deoxyribonucleotides or ribonucleotides.
- Prader-Willi syndrome -- a condition characterized
by obesity and insatiable appetite, mental deficiency, small genitals, and short stature.
May be deletion of #15 chromosome.
- Predisposition -- to have a tendency or inclination
towards something in advance.
- Presymptomatic diagnosis -- diagnosis of a genetic
condition before the appearance of symptoms.
- Primer -- nucleotides used in the polymerase chain
reaction to initiate DNA synthesis at a particular location.
- Probability -- the long term frequency of an event
relative to all alternative events, and usually expressed as decimal fraction.
- Proband -- individual in a family who brought the
family to medical attention.
- Probe -- single-stranded DNA labeled with
radioactive isotopes or tagged in other ways for ease in identification.
- Prognosis -- prediction of the course and probable
outcome of a disease.
- Proteus syndrome -- a condition characterized by
distorted asymmetric growth of the body and enlarged head, enlarged feet, multiple nevi on
the skin; mode of inheritance is unknown.
- Public policy -- a set of action guidelines or rules
that result from the actions or lack of actions of governmental entities.
- Recessive -- a gene that is
phenotypically manifest in the homozygous state but is masked in the presence of a
- Recombination -- the natural process of breaking and
rejoining DNA strands to produce new combinations of genes and, thus, generate genetic
variation. Gene crossover during meiosis.
- Repeat sequences -- the length of a nucleotide
sequence that is repeated in a tandem cluster.
- Retinitis pigmentosa -- group of hereditary ocular
disorders with progressive retinal degeneration. Autosomal dominant, autosomal recessive,
and x-linked forms.
- Retinoblastoma -- a childhood malignant cancer of
the retina of the eye. reverse transcriptase viral enzyme used to make cDNA.
- RFLP -- restriction fragment length polymorphism;
variations occurring within a species in the length of DNA fragments generated by a
- Ribosomal protein -- one of the ribonucleoprotein
particles that are the sites of translation.
- Rubinstein-Taybi syndrome -- condition with multiple
congenital anomalies including: mental deficiency, broad thumbs, small head, broad nasal
bridge and beaked nose.
- Sanger sequence -- "plus and
minus" or "primed synthesis" method; DNA is synthesized so it is
radioactively labeled and the reaction terminates specifically at the position
corresponding to a given base.
- Selection -- the process of determining the relative
share allotted individuals of different genotypes in the propagation of a population; the
selective effect of a gene can be defined by the probability that carriers of the gene
- Sex determination -- the mechanism in a given
species by which sex is determined; in many species sex is determined at fertilization by
the nature of the sperm that fertilizes the egg.
- Sickle cell anemia -- an hereditary, chronic form of
hemolytic anemia characterized by breakdown of the red blood cells; red blood cells
undergo a reversible alteration in shape when the oxygen tension of the plasma falls
slightly and a sickle-like shape forms.
- Somatic cell hybrid -- hybrid cell line derived from
two different species; contains a complete chromosomal complement of one species and a
partial chromosomal complement of the other; human/hamster hybrids grow and divide, losing
human chromosomes with each generation until they finally stabilize, the hybrid cell line
established is then utilized to detect the presence of genes on the remaining human
- Somatic mutation -- a mutation occurring in any cell
that is not destined to become a germ cell; if the mutant cell continues to divide, the
individual will come to contain a patch of tissue of genotype different from the cells of
the rest of the body.
- Southern blotting -- a technique for transferring
electrophoretically resolved DNA segments from an agarose gel to a nitrocellulose filter
paper sheet via capillary action; the DNA segment of interest is probed with a
radioactive, complementary nucleic acid, and its position is determined by
- Spina bifida -- a congenital condition that results
from altered fetal development of the spinal cord, part of the neural plate fails to join
together and bone and muscle are unable to grow over this open section.
- Syndrome -- a recognizable pattern or group of
multiple signs, symptoms or malformations that characterize a particular condition;
syndromes are thought to arise from a common origin and result from more than one
developmental error during fetal growth.
- Tay-Sachs disease -- a fatal
degenerative disease of the nervous system due to a deficiency of hexosamidase A, causing
mental deficiency, paralysis, mental deterioration, and blindness; found primarily but not
exclusively among Ashkenazi Jews. Autosomal recessive.
- Teratogens -- any agent that raises the incidence of
- 3' - end -- the end of a polynucleotide with a free
(or phosphorylated) 3' - hydroxyl group.
- Trait -- any detectable phenotypic property of an
- Transduction -- the transfer of bacterial genetic
material from one bacterium to another using a phage as a vector.
- Transferase -- enzymes that catalyze the transfer of
functional groups between donor and acceptor molecules.
- Transcription -- the formation of an RNA molecule
upon a DNA template by complementary base pairing.
- Translation -- the formation of a polypeptide chain
in the specific amino acid sequence directed by the genetic information carried by mRNA.
- Translocation -- a chromosome aberration which
results in a change in position of a chromosomal segment within the genome, but does not
change the total number of genes present.
- Triplet code -- a code in which a given amino acid
is specified by a set of three nucleotides.
- Tumor suppressor gene -- genes that normally
function to restrain the growth of tumors; the best understood case is for hereditary
- Transgenic organism -- one into which a cloned
genetic material has been experimentally transferred, a subset of these foreign gene
express themselves in their offspring.Turner syndrome a chromosomal condition in females
(usually 45,XO) due to monosomy of the X- chromosome; characterized by short stature,
failure to develop secondary sex characteristics, and infertility.
- UNESCO -- United National
Educational, Scientific, and Cultural Organization.
- VNTR -- variable number tandem
repeats; any gene whose alleles contain different numbers of tandemly repeated
- Vector -- a self-replicating DNA molecule that
transfers a DNA segment between host cells.
- Von Hippel-Lindau syndrome -- an autosomal dominant
condition characterized by the anomalous growth and proliferation of blood vessels on the
retina of the eye and the cerebellum of the brain; cysts and cancers in the kidneys,
pancreas, and adrenal glands.
- Western blotting analysis -- a
technique used to identify a specific protein; the probe is a radioactively labeled
antibody raised against the protein in question.
- X-inactivation -- the repression of
one of the two X-chromosomes in the somatic cells of females as a method of dosage
compensation; at an early embryonic stage in the normal female, one of the two
X-chromosomes undergoes inactivation, apparently at random, from this point on all
descendent cells will have the same X-chromosome inactivated as the cell from which they
arose, thus a female is a mosaic composed of two types of cells, one which expresses only
the paternal X-chromosome, and another which expresses only the maternal X-chromosome.
- XYY syndrome -- genetic condition in males with
extra Y chromosome (in 1 in 1000 male births). Symptoms: tall stature (over 6'), may
including sterility, developmental delay, learning problems.
- YAC -- yeast artificial chromosome;
a linear vector into which a large fragment of DNA can be inserted; the development of
YAC's in 1987 has increased the number of nucleotides which can be cloned.
- Zoo blot -- northern analysis of
mRNA from different organisms.
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