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175 Cards in this Set

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adenosine deaminase deficiency: ADA
A severe immunodeficiency disease that results from a lack of the enzyme adenosine deaminase. It usually leads to death within the first few months of life.
adenovirus
A group of DNA containing viruses which cause respiratory disease, including one form of the common cold. Adenoviruses can also be genetically modified and used in gene therapy to treat cystic fibrosis, cancer, and potentially other diseases.
Alagille syndrome
A rare inherited liver disorder seen in infants and young children. The disease is characterized by a buildup of bile in the liver due to a deficiency or absence of normal bile ducts inside the liver and a narrowing of bile ducts outside the liver. Symptoms of the disorder can include jaundice, stunted growth, fatty deposits in the skin, facial deformities, and abnormalities in the heart, eyes, vertebrae, and kidneys.
amino acids
A laboratory animal useful for medical research because it has specific characteristics that resemble a human disease or disorder. Scientists can create animal models, usually laboratory mice, by transferring new genes into them
antibody
A blood protein that is produced in response to and counteracts an antigen. Antibodies are produced in response to disease and help the body fight against the particular disease. In this way, antibodies help the body develop an immunity to disease.
antisense
The non-coding strand in double-stranded DNA. The antisense strand serves as the template for mRNA synthesis.
apoptosis
Programmed cell death, the body's normal method of disposing of damaged, unwanted, or unneeded cells.
ataxia-telangiectasia
A rare fatal disease involving a damaged immune system, unsteady walk, premature aging, and a strong predisposition to some kinds of cancer. People who possess only one copy of the gene, called ATM, do not have the disease, but may be predisposed to cancer and unusually sensitive to radiation.
Autoimmune Lymphoproliferativ syndrome
human disease caused by failure of lymphocytes to die once they have finished doing their job. As a result, the spleen and lymph nodes grow large, and immune cells may attack the body's own tissues, a condition known as autoimmunity.
autosomal dominant
pattern of Mendelian inheritance whereby an affected individual possesses one copy of a mutant allele and one normal allele. (In contrast, recessive diseases require that the individual have two copies of the mutant allele.) Individuals with autosomal dominant diseases have a 50-50 chance of passing the mutant allele and hence the disorder onto their children. Examples of autosomal dominant diseases include Huntington's disease, neurofibromatosis, and polycystic kidney disease.
autosome
Any chromosome other than a sex chromosome. Humans have 22 pairs of autosomes.
bacteria
A single-celled organism. Bacteria are found throughout nature and can be beneficial or pathogenic
bacterial artificial chromosome (BAC)
Large segments of DNA, 100,000 to 200,000 bases, from another species cloned into bacteria. Once the foreign DNA has been cloned into the host bacteria, many copies of it can be made.
base pair
adenine always pairs with thymine, and guanine always pairs with cytosine.
birth defect
A structural, functional, or metabolic abnormality present at birth that results in physical or mental disability or is fatal. There are more than 4,000 known birth defects, which may be caused by genetic or environmental factors. About 150,000 babies are born each year with birth defects.
bone marrow transplantation
A medical procedure to replenish the soft tissue within bones that produces new blood cells. Bone marrow transplants are necessary when marrow has been destroyed by drug or radiation therapy for cancer, often leukemia. A bone marrow donor is usually a close relative of the patient.
BRCA1/BRCA2
The first breast cancer genes to be identified. Mutated forms of these genes are believed to be responsible for about half the cases of inherited breast cancer, especially those that occur in younger women. Both are tumor suppressor genes.
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 also be fatal if not treated adequately.
candidate gene
A gene, located in a chromosome region suspected of being involved in a disease, whose protein product suggests that it could be the disease gene in question.
carcinoma
Any of the various types of cancerous tumors that form in the epithelial tissue, the tissue forming the outer layer of the body surface and lining the digestive tract and other hollow structures. Examples of this kind of cancer include, breast, lung, and prostate cancer.
carrier
carrier An individual who possesses one copy of a mutant allele that causes disease only when two copies are present. Although carriers not affected by the disease, two carriers can produce a child who has the disease.
cDNA library
A collection of DNA sequences generated from mRNA sequences. This type of library contains only protein-coding DNA (genes) and does not include any non-coding DNA
cell
The basic unit of any living organism. It is a small, watery, compartment filled with chemicals and a complete copy of the organism's genome.
centimorgan
A measure of genetic distance that tells how far apart two genes are. Generally one centimorgan equals about 1 million base pairs.
centromere
The constricted region near the center of a human chromosome. This is the region of the chromosome where the two sister chromatids are joined to one another.
chromosome
One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers
cloning
The process of making copies of a specific piece of DNA, usually a gene. When geneticists speak of cloning, they do not mean the process of making genetically identical copies of an entire organism
codon
Three bases in a DNA or RNA sequence which specify a single amino acid.
congenital
Any trait or condition that exists from birth.
contig
A chromosome map showing the locations of those regions of a chromosome where contiguous DNA segments overlap. Contig maps are important because they provide the ability to study a complete, and often large segment of the genome by examining a series of overlapping clones which then provide an unbroken succession of information about that region.
craniosynostosis
A birth defect whereby an infant's skull bones are already fused at birth. Because this defect may interfere with the ability of the brain to grow normally, it is often necessary to operate on affected children.
cystic fibrosis
A hereditary disease whose symptoms usually appear shortly after birth. They include faulty digestion, breathing difficulties and respiratory infections due to mucus accumulation, and excessive loss of salt in sweat. In the past, cystic fibrosis was almost always fatal in childhood, but treatment is now so improved that patients commonly live to their 20s and beyond.
cytogenetic map
The visual appearance of a chromosome when stained and examined under a microscope. Particularly important are visually distinct regions, called light and dark bands, which give each of the chromosomes a unique appearance. This feature allows a person's chromosomes to be studied in a clinical test known as a karyotype, which allows scientists to look for chromosomal alterations.
cytosine
One of the four bases in DNA that make up the letters ATGC, always pairs with guanine.
deletion
A particular kind of mutation: loss of a piece of DNA from a chromosome. Deletion of a gene or part of a gene can lead to a disease or abnormality
deoxyribonucleic acid (DNA)
The chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.
diabetes mellitus
Two types of a highly variable disorder in which abnormalities in the ability to make and/or use the hormone insulin interfere with the process of turning dietary carbohydrates into glucose, the body's fuel. Type I is known as insulin dependent diabetes mellitus, and type II is known as non-insulin dependent diabetes mellitus
diploid
The number of chromosomes in most cells except the gametes. In humans, the diploid number is 46.
DNA replication
The process by which the DNA double helix unwinds and makes an exact copy of itself.
DNA sequencing
Determining the exact order of the base pairs in a segment of DNA.
dominant
A gene that almost always results in a specific physical characteristic, for example, a disease, even though the patient's genome possesses only one copy. With a dominant gene, the chance of passing on the gene (and therefore the disease) to children is 50-50 in each pregnancy.
double helix
The structural arrangement of DNA, which looks something like an immensely long ladder twisted into a helix, or coil. The sides of the "ladder" are formed by a backbone of sugar and phosphate molecules, and the "rungs" consist of nucleotide bases joined weakly in the middle by hydrogen bonds.
duplication
A particular kind of mutation: production of one or more copies of any piece of DNA, including a gene or even an entire chromosome.
electrophoresis
The process in which molecules (such as proteins, DNA, or RNA fragments) can be separated according to size and electrical charge by applying an electric current to them. The current forces the molecules through pores in a thin layer of gel, a firm jelly-like substance. The gel can be made so that its pores are just the right dimensions for separating molecules within a specific range of sizes and shapes. Smaller fragments usually travel further than large ones. The process is sometimes called gel electrophoresis.
Ellis - van Creveld syndrome
A rare autosomal recessive disorder that leads to dwarfism, extra fingers, and malformations of the heart, among other abnormalities.
enzyme
A rare autosomal recessive disorder that leads to dwarfism, extra fingers, and malformations of the heart, among other abnormalities.
exon
The region of a gene that contains the code for producing the gene's protein. Each exon codes for a specific portion of the complete protein. In some species (including humans), a gene's exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function.
familial Mediterranean fever
An inherited disease whose chief symptoms are recurrent fevers and severe abdominal pain due to inflammation of the abdominal cavity. Other symptoms include arthritis, chest pain from inflammation of the lung cavity, and skin rashes.
fibroblasts
A type of cell found just underneath the surface of the skin. Fibroblasts are part of the support structure for tissues and organs.
fluorescence in situ hybridization (FISH)
A process which vividly paints chromosomes or portions of chromosomes with fluorescent molecules. This technique is useful for identifying chromosomal abnormalities and gene mapping.
Fragile X syndrome
After Down syndrome, the second most frequent genetic cause of mental retardation. The disorder is one of a group of diseases that results from an unusual kind of mutation: an expansion of a repeating sequence of three letters of the DNA code, called a triplet repeat or trinucleotide repeat. the repeating triplet is CGG, cytosine-guanine-guanine, in a gene called FMR1 on the X chromosome. There are ordinarily fewer than 55 copies of the repeat. When the number of repeats exceeds 200, the expansion is called a "full mutation" and expression of the FMR1 gene is shut off
gene
The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein
gene amplification
An increase in the number of copies of any particular piece of DNA. A tumor cell amplifies, or copies, DNA segments naturally as a result of cell signals and sometimes environmental events.
gene expression
The process by which proteins are made from the instructions encoded in DNA
gene mapping
Determining the relative positions of genes on a chromosome and the distance between them.
gene pool
The sum total of genes, with all their variations, possessed by a particular species at a particular time.
gene therapy
An evolving technique used to treat inheritied diseases. The medical procedure involves either replacing, manipulating, or supplementing nonfunctional genes with healthy genes.
gene transfer
Insertion of unrelated DNA into the cells of an organism. There are many different reasons for gene transfer: for example, attempting to treat disease by supplying patients with therapeutic genes. There are also many possible ways to transfer genes. Most involve the use of a vector, such as a specially modified virus that can take the gene along when it enters the cell.
genetic code (ATGC)
The instructions in a gene that tell the cell how to make a specific protein. A, T, G, and C are the "letters" of the DNA code; they stand for the chemicals adenine, thymine, guanine, and cytosine, respectively, that make up the nucleotide bases of DNA. Each gene's code combines the four chemicals in various ways to spell out 3-letter "words" that specify which amino acid is needed at every step in making a protein.
genetic counseling
A short-term educational counseling process for individuals and families who have a genetic disease or who are at risk for such a disease. Genetic counseling provides patients with information about their condition and helps them make informed decisions.
genetic map
(Also known as a linkage map) a chromosome map of a species that shows the position of its known genes and/or markers relative to each other, rather than as specific physical points on each chromosome.
genetic marker
A segment of DNA with an identifiable physical location on a chromosome and whose inheritance can be followed. A marker can be a gene, or it can be some section of DNA with no known function. Because DNA segments that lie near each other on a chromosome tend to be inherited together, markers are often used as indirect ways of tracking the inheritance pattern of a gene that has not yet been identified, but whose approximate location is known.
genetic screening
Testing a population group to identify a subset of individuals at high risk for having or transmitting a specific genetic disorder.
genome
All the DNA contained in an organism or a cell, which includes both the chromosomes within the nucleus and the DNA in mitochondria.
genotype
The genetic identity of an individual that does not show as outward characteristics.
germ line
Inherited material that comes from the eggs or sperm and is passed on to offspring.
guanine
always pairs with cytosine.
haploid
The number of chromosomes in a sperm or egg cell, half the diploid number.
haploinsufficiency
A situation in which the protein produced by a single copy of an otherwise normal gene is not sufficient to assure normal function.
hematopoietic stem cell
An unspecialized precursor cell that will develop into a mature blood cell.
hemophilia
A sex-linked inherited bleeding disorder that generally only affects males. The disorder is characterized by a tendency to bleed spontaneously or at the slightest injury because of the lack of certain clotting factors in the blood.
heterozygous
Possessing two different forms of a particular gene, one inherited from each parent.
highly conserved sequence
A DNA sequence that is very similar in several different kinds of organisms. Scientists regard these cross species similarities as evidence that a specific gene performs some basic function essential to many forms of life and that evolution has therefore conserved its structure by permitting few mutations to accumulate in it.
Hirschsprung's disease
A congenital disorder in which part of the colon lacks nerve cells and therefore is unable to relax. The result is chronic constipation and distention of the abdomen. The disorder affects about one in 5000 U.S. newborns but can be treated with surgery.
holoprosencephaly
A birth defect where the forebrain does not separate properly into two halves during early fetal life. The disorder results in mild to severe brain malformation and is sometimes fatal. It may be caused by environmental or genetic factors. Holoprosencephaly affects between 1 in 5,000 and 1 in 10,000 live births.
homologous recombination
The exchange of pieces of DNA during the formation of eggs and sperm. Recombination allows the chromosomes to shuffle their genetic material, increasing the potential of genetic diversity. Homologous recombination is also known as crossing over.
homozygous
Possessing two identical forms of a particular gene, one inherited from each parent.
human artificial chromosome (HAC)
A vector used to transfer or express large fragments of human DNA. HACs behave and are constructed like human chromosomes
Human Genome Project
An international research project to map each human gene and to completely sequence human DNA.
human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS)
Was first reported in 1981 in the United States and has since become a major epidemic, killing nearly 12 million people and infecting more than 30 million others worldwide.
Huntington's disease
A degenerative brain disorder that usually appears in mid-life. Its symptoms, which include involuntary movement of the face and limbs, mood swings, and forgetfulness, get worse as the disease progresses. It is generally fatal within 20 years.
hybridization
Base pairing of two single strands of DNA or RNA.
immunotherapy
The concept of using the immune system to treat disease, for example, developing a vaccine against cancer. Immunotherapy may also refer to the therapy of diseases caused by the immune system, allergies for example.
in situ hybridization
The base pairing of a sequence of DNA to metaphase chromosomes on a microscope slide.
inherited
Transmitted through genes from parents to offspring.
insertion
A type of chromosomal abnormality in which a DNA sequence is inserted into a gene, disrupting the normal structure and function of that gene.
intellectual property rights
Patents, copyrights, and trademarks.
intron
A noncoding sequence of DNA that is initially copied into RNA but is cut out of the final RNA transcript.
karyotype
The chromosomal complement of an individual, including the number of chromosomes and any abnormalities. The term is also used to refer to a photograph of an individual's chromosomes.
knockout
Inactivation of specific genes. Knockouts are often created in laboratory organisms such as yeast or mice so that scientists can study the knockout organism as a model for a particular disease.
leukemia
Cancer of the developing blood cells in the bone marrow. Leukemia leads to rampant overproduction of white blood cells (leukocytes); symptoms usually include anemia, fever, enlarged liver, spleen, and/or lymph nodes.
library
A collection of cloned DNA, usually from a specific organism.
linkage
The association of genes and/or markers that lie near each other on a chromosome. Linked genes and markers tend to be inherited together.
locus
The place on a chromosome where a specific gene is located, a kind of address for the gene. The plural is "loci," not "locuses."
LOD score
A statistical estimate of whether two loci are likely to lie near each other on a chromosome and are therefore likely to be inherited together. A LOD score of three or more is generally taken to indicate that the two loci are close.
lymphocyte
A small white blood cell that plays a major role in defending the body against disease. There are two main types of lymphocytes: B cells, which make antibodies that attack bacteria and toxins, and T cells, which attack body cells themselves when they have been taken over by viruses or become cancerous.
malformation
A structural defect inherited in an organ or part of an organ that results from abnormal fetal development.
mapping
The process of deducing schematic representations of DNA. Three types of DNA maps can be constructed: physical maps, genetic maps, and cytogenetic maps, with the key distinguishing feature among these three types being the landmarks on which they are based.
marker
Also known as a genetic marker, a segment of DNA with an identifiable physical location on a chromosome whose inheritance can be followed. A marker can be a gene, or it can be some section of DNA with no known function. Because DNA segments that lie near each other on a chromosome tend to be inherited together, markers are often used as indirect ways of tracking the inheritance pattern of genes that have not yet been identified, but whose approximate locations are known.
melanoma
Cancer of the cells in the skin that produce melanin, a brown pigment. Melanoma often begins in a mole.
Mendel, Johann (Gregor)
Austrian biologist, who laid the foundations for the science of genetics. Concluded that the heritable units we now call genes were not blends of parental traits but separate physical entities passed individually in specific proportions from one generation to the next.
Mendelian inheritance
Manner in which genes and traits are passed from parents to children. Examples of Mendelian inheritance include autosomal dominant, autosomal recessive, and sex-linked genes.
messenger RNA (mRNA)
Template for protein synthesis. Each set of three bases, called codons, specifies a certain protein in the sequence of amino acids that comprise the protein. The sequence of a strand of mRNA is based on the sequence of a complementary strand of DNA.
metaphase
The phase of mitosis, or cell division, when the chromosomes align along the center of the cell. Because metaphase chromosomes are highly condensed, scientists use these chromosomes for gene mapping and identifying chromosomal aberrations.
microarray technology
A new way of studying how large numbers of genes interact with each other and how a cell's regulatory networks control vast batteries of genes simultaneously. The method uses a robot to precisely apply tiny droplets containing functional DNA to glass slides. Researchers then attach fluorescent labels to DNA from the cell they are studying. The labeled probes are allowed to bind to complementary DNA strands on the slides. The slides are put into a scanning microscope that can measure the brightness of each fluorescent dot; brightness reveals how much of a specific DNA fragment is present, an indicator of how active it is.
microsatellite
Repetitive stretches of short sequences of DNA used as genetic markers to track inheritance in families.
mitochondrial DNA
The genetic material of the mitochondria, the organelles that generate energy for the cell.
monosomy
Possessing only one copy of a particular chromosome instead of the normal two copies.
mouse model
A laboratory mouse useful for medical research because it has specific characteristics that resemble a human disease or disorder. Strains of mice having natural mutations similar to human ones may serve as models of such conditions. Scientists can also create mouse models by transferring new genes into mice or by inactivating certain existing genes in them.
multiple endocrine neoplasia, type 1 (MEN1)
A rare inherited disorder that affects the endocrine glands, which release hormones into the bloodstream. The disorder, also known as Wermer's syndrome, can cause multiple tumors in the parathyroid and pituitary glands and in the pancreas. These tumors are almost always benign, but they can cause the glands to become overactive and secrete abnormal levels of hormones. Those abnormal secretions, in turn, can cause a variety of medical problems, ranging from kidney stones and fatigue to fertility problems and life-threatening ulcers.
mutation
A permanent structural alteration in DNA. In most cases, DNA changes either have no effect or cause harm, but occasionally a mutation can improve an organism's chance of surviving and passing the beneficial change on to its descendants.
neurofibromatosis
An inherited progressive disorder in which tumors form on peripheral nerves. The tumors can be severely disfiguring and can also result in loss of hearing and vision, cancer, epilepsy, bone deformities, and learning disabilities.
Niemann-Pick disease, type C (NPC)
A disease that causes progressive deterioration of the nervous system by blocking movement of cholesterol within cells. The gene responsible for it, known as NPC1, is located on human chromosome 18.
non-coding DNA
The strand of DNA that does not carry the information necessary to make a protein. The non-coding strand is the mirror image of the coding strand and is also known as the antisense strand.
non-directiveness
The process by which genetic counselors advise clients toward a certain test or outcome, particularly related to child-bearing issues, without pressure or coercion.
nonsense mutation
A single DNA base substitution resulting in a stop codon.
Northern blot
A technique used to identify and locate mRNA sequences that are complementary to a piece of DNA called a probe.
nucleotide
One of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base (one of four chemicals: adenine, thymine, guanine, and cytosine) plus a molecule of sugar and one of phosphoric acid.
nucleus
The central cell structure that houses the chromosomes.
oligo
Oligonucleotide, short sequence of single-stranded DNA or RNA. Oligos are often used as probes for detecting complementary DNA or RNA because they bind readily to their complements.
oncogene
A gene that is capable of causing the transformation of normal cells into cancer cells.
oncovirus
A class of retroviruses that cause a cell to become cancerous.
p53
A gene which normally regulates the cell cycle and protects the cell from damage to its genome. Mutations in this gene cause cells to develop cancerous abnormalities.
Parkinson's disease
A common progressive neurological disorder that results from degeneration of nerve cells in a region of the brain that controls movement. The first symptom of the disease is usually tremor of a limb, especially when the body is at rest.
patent
When applied to genetics, the government regulations or requirements conferring the right or title to an individual or organization to genes if there has been substantial human intervention.
pedigree
A simplified diagram of a family's genealogy that shows family members' relationships to each other and how a particular trait or disease has been inherited.
peptide
Two or more amino acids joined by a peptide bond.
phenotype
The observable traits or characteristics of an organism, for example hair color, weight, or the presence or absence of a disease. Phenotypic traits are not necessarily genetic.
physical map
A chromosome map of a species that shows the specific physical locations of its genes and/or markers on each chromosome. Physical maps are particularly important when searching for disease genes by positional cloning strategies and for DNA sequencing.
polydactyly
An abnormality in which a person is born with more than the normal number of fingers or toes.
polymerase chain reaction (PCR)
A fast, inexpensive technique for making an unlimited number of copies of any piece of DNA. Sometimes called "molecular photocopying," PCR has had an immense impact on biology and medicine, especially genetic research.
polymorphism
A common variation in the sequence of DNA among individuals.
positional cloning
A process which, through gene mapping techniques, is able to locate a gene responsible for a disease when little or no information is known about the biochemical basis of the disease.
primary immunodeficiency
A group of rare inherited disorders of the immune system, including adenosine deaminase deficiency, severe combined immunodeficiency (SCID), and ataxia-telangectasia.
primer
A short oligonucleotide sequence used in a polymerase chain reaction.
probe
A piece of labeled DNA or RNA or an antibody used to detect the function of a gene.
promoter
The part of a gene that contains the information to turn the gene on or off. The process of transcription is initiated at the promoter.
pronucleus
The nucleus of a sperm or an egg prior to fertilization. Sperm and egg cells carry half the number of chromosomes of other nonreproductive cells. When the pronucleus of a sperm fuses with the pronucleus of an egg, their chromosomes combine and become part of a single nucleus in the resulting embryo, containing a full set of chromosomes.
prostate cancer
Cancer only in men, surrounds the neck of the bladder and the urethra.
protease
A protein that digests other proteins.
protein
A large complex molecule made up of one or more chains of amino acids. Proteins perform a wide variety of activities in the cell.
pseudogene
A sequence of DNA that is very similar to a normal gene but that has been altered slightly so it is not expressed. Such genes were probably once functional but over time acquired one or more mutations that rendered them incapable of producing a protein product.
recessive
A genetic disorder that appears only in patients who have received two copies of a mutant gene, one from each parent.
recombinant DNA
A variety of techniques that molecular biologists use to manipulate DNA molecules to study the expression of a gene.
repressor
A protein that regulates a gene by turning it off.
restriction enzymes
Enzymes that recognize a specific sequence of double-stranded DNA and cut the DNA at that site. Restriction enzymes are often referred to as molecular scissors.
restriction fragment length polymorphism (RFLP)
Genetic variations at the site where a restriction enzyme cuts a piece of DNA. Such variations affect the size of the resulting fragments. These sequences can be used as markers on physical maps and linkage maps. RFLP is also pronounced "rif" lip.
retrovirus
A type of virus that contains RNA as its genetic material. The RNA of the virus is translated into DNA, which inserts itself into an infected cell's own DNA. Retroviruses can cause many diseases, including some cancers and AIDS.
ribonucleic acid (RNA)
A chemical similar to a single strand of DNA. In RNA, the letter U, which stands for uracil, is substituted for T in the genetic code. RNA delivers DNA's genetic message to the cytoplasm of a cell where proteins are made.
ribosome
Cellular organelle that is the site of protein synthesis
risk communication
An educational process through which a genetic counselor attempts to interpret how a genetic condition is inherited and the chances that it might be passed on to children.
sequence-tagged site (STS)
A short DNA segment that occurs only once in the human genome and whose exact location and order of bases are known. Because each is unique, STSs are helpful for chromosome placement of mapping and sequencing data from many different laboratories. STSs serve as landmarks on the physical map of the human genome.
severe combined immunodeficiency (SCID)
A disease affecting the immune system. SCID is fatal if affected individuals do not receive bone marrow transplants.
sex chromosome
One of the two chromosomes that specify an organism's genetic sex. Humans have two kinds of sex chromosomes, one called X and the other Y. Normal females possess two X chromosomes and normal males one X and one Y.
sex-linked
Located on the X chromosome. Sex-linked (or x-linked) diseases are generally seen only in males.
shotgun sequencing
An approach used to decode an organism's genome by shredding it into smaller fragments of DNA which can be sequenced individually. The sequences of these fragments are then ordered, based on overlaps in the genetic code, and finally reassembled into the complete sequence. The 'whole genome shotgun' method is applied to the entire genome all at once, while the 'hierarchical shotgun' method is applied to large, overlapping DNA fragments of known location in the genome.
sickle cell disease
A blood condition seen most commonly in people of African ancestry. The disorder is caused by a single base pair change in one of the genes that codes for hemoglobin, the blood protein that carries oxygen. This mutation causes the red blood cells to take on a sickle shape, rather than their characteristic donut shape. Individuals who suffer from sickle cell disease are chronically anemic and experience significant damage to their heart, lungs, and kidneys.
single nucleotide polymorphisms (SNPs)
Common, but minute, variations that occur in human DNA at a frequency of one every 1,000 bases. These variations can be used to track inheritance in families. SNP is pronounced "snip".
somatic cells
All body cells, except the reproductive cells.
Southern blot
A technique used to identify and locate DNA sequences which are complementary to another piece of DNA called a probe.
spectral karyotype (SKY)
A visualization of all of an organism's chromosomes together, each labeled with a different color. This technique is useful for identifying chromosome abnormalities.
substitution
Replacement of one nucleotide in a DNA sequence by another nucleotide or replacement of one amino acid in a protein by another amino acid.
suicide gene
A strategy for making cancer cells more vulnerable to chemotherapy. One approach has been to link parts of genes expressed in cancer cells to other genes for enzymes not found in mammals that can convert a harmless substance into one that is toxic to the tumor.
syndrome
The group or recognizable pattern of symptoms or abnormalities that indicate a particular trait or disease.
technology transfer
The process of providing the private sector access to technological advances developed by scientists in the Federal government.
thymine
Always pairs with adenine.
transgenic
An experimentally produced organism in which DNA has been artificially introduced and incorporated into the organism's germ line, usually by injecting the foreign DNA into the nucleus of a fertilized embryo.
translocation
Breakage and removal of a large segment of DNA from one chromosome, followed by the segment's attachment to a different chromosome.
trisomy
Possessing three copies of a particular chromosome instead of the normal two copies.
tumor suppressor gene
A protective gene that normally limits the growth of tumors. When a tumor supressor is mutated, it may fail to keep a cancer from growing. BRCA1 and p53 are well-known tumor suppressor genes.
uracil
One of the four bases in RNA. Always pairs with adenine.
vector
An agent, such as a virus or a small piece of DNA called a plasmid, that carries a modified or foreign gene. When used in gene therapy, a vector delivers the desired gene to a target cell.
Western blot
A technique used to identify and locate proteins based on their ability to bind to specific antibodies.
Wolfram syndrome
A rare autosomal recessive disorder that leads to many different abnormalities, including diabetes mellitus, deafness, and blindness. Patients usually also suffer from severe abnormalities of the nervous system that can be accompanied by behavior problems, psychiatric hospitalizations, and, in 25 percent of cases, suicide attempts.
yeast artificial chromosome (YAC)
Extremely large segments of DNA from another species spliced into DNA of yeast. YACs are used to clone up to one million bases of foreign DNA into a host cell, where the DNA is propagated along with the yeast cell's other chromosomes.