basic building blocks of proteins. There are 20 different amino acid
types. Each protein consists of a different sequence of amino acids
linked together according to the genetic information encoded in DNA.
paired chromosome that is alike in the cells of males and females,
as distinguished from the sex chromosomes X or Y. Humans have 22 pairs
of complementary nitrogenous bases that interact to form each rung
of DNA's double helix. Adenine (A) pairs with thymine (T); cytosine
(C) pairs with guanine (G).
small worm that is used as a model organism to study genetics and
basic subunit of any living organism; the simplest unit that can exist
as an independent living system.
structure of DNA and protein found in the cell nucleus. Each chromosome
contains hundreds or thousands of the genes that form our hereditary
blueprint. Humans have 23 pairs of chromosomes (each parent contributes
one chromosome in each pair), containing a total of 50,000 to 100,000
genes from each parent.
research technique developed to move rapidly up or down a chromosome
in search of a particular gene. It enables researchers to make large
jumps over uninformative regions of DNA.
research technique in which overlapping fragments of a chromosome
are checked one at a time in search of a particular gene. It covers
smaller regions than chromosome jumping.
single strand of DNA synthesized in the lab to complement the bases
in a given strand of messenger RNA. Complementary DNA represents the
parts of a gene that are expressed in a cell to produce a protein.
of DNA that have remained largely unchanged throughout evolution.
Conserved DNA sequences are believed to be involved in important functions
that are similar in different species.
genetic disease involving a sticky buildup of mucus in the lungs (which
makes breathing difficult and leads to infections), as well as pancreatic
insufficiency (which leads to digestive problems). It is a recessive
disease, occurring only when a child inherits two mutated copies of
the CF gene--one from each parent.
to help patients and families with information and referrals about
cystic fibrosis. Headquarters: 6931 Arlington Road, Bethesda, MD 20814.
Toll-free phone: (800)FIGHT-CF. Or call (301)951-4422. Email: firstname.lastname@example.org.
Home page: www.cff.org.
to a characteristic that is apparent even when the relevant gene is
present in only one copy. A dominant disorder can be inherited from
only one parent.
genetic material of living organisms; the substance of heredity. It
is a large, double-stranded, helical molecule that contains genetic
instructions for growth, development, and replication. The rungs of
this double helix are made of base pairs.
specific sequence of single-stranded DNA used to seek out a complementary
sequence of single-stranded DNA. Probes are usually labelled radioactively
or chemically to make them easier to detect, thus revealing the target
type of fruit fly used as a model organism to study genetics and development.
genetic disease that prevents muscles from developing properly in
early childhood and may be crippling. Primarily affecting males, it
is caused by a mutant gene on the X chromosome.
stem (ES) cells
embryonic cells (usually mouse cells) that can be genetically manipulated
by researchers and then implanted into embryos to produce transgenic
animals (usually mice) with predetermined genetic mutations.
segment of a gene that contains instructions for making a protein.
In many genes the exons are separated by "intervening" segments of
DNA, known as introns, which do not code for proteins; these introns
are removed by splicing to produce messenger RNA.
sequence of DNA that represents a fundamental unit of heredity. Most
genes encode proteins, but some code for RNA molecules.
a gene and producing many identical copies of it so that it can be
studied in detail.
process by which the information encoded in a gene is converted into
protein or some form of RNA. The DNA sequence is first transcribed
into RNA and then usually--but not always--translated into protein.
linkage map (also called linkage map)
map of the relative positions of genetic loci on a chromosome. Genes
that are generally inherited together are located close to each other
on the chromosome and said to be linked.
method scientists use to alter or turn off a particular gene in animals
used in research.
of a disease by introducing a new gene into a cell. The new gene may
be used to replace a function that is missing because of a defective
process by which a gene's DNA sequence is copied into messenger RNA;
the first step in gene expression.
process by which transcribed messenger RNA directs the synthesis of
proteins from amino acids.
disease caused by a genetic mutation that is either inherited or arises
landmark that identifies a unique location on a chromosome.
of a population to identify people at risk for a specific genetic
disease or at risk for transmitting such a disease to their children.
scientist who studies genes, the basic units of heredity, and their
total genetic information of a particular organism. The normal human
genome consists of 3 billion base pairs of DNA in each set of 23 chromosomes
from one parent.
that give rise to sperm or egg.
to research and information on Huntington's disease. Headquarters:
1427 7th Street, #2, Santa Monica, CA 90401. Telephone: (310) 458-4183.
Fax: (310) 458-3937. Email: email@example.com.
Home page: www.hdfoundation.org.
process by which one DNA segment can replace another DNA segment that
has a similar sequence. Homologous recombination is used by researchers
to create "knockout" mice in which the function of a specific gene
large international project to map and sequence all the DNA in human
genetic disease of the central nervous system that produces progressive
dementia and involuntary movements. It usually starts between ages
30 and 50 and slowly progresses to death. Since it is a dominant disease,
a child of a parent with Huntington's disease has a 50-50 chance of
DNA sequences that interrupt the sequences containing instructions
for making a protein (exons). Introns are not represented in messenger
RNA; only the exons are translated into protein. The function of introns
is still being explored.
of an egg and a sperm outside of the mother's body to create an embryo
that is implanted in her uterus.
mice created by disrupting the function of a specific gene.
transcribed from the DNA making up a gene. It transmits genetic information
from the nucleus to the cytoplasm, where it directs the synthesis
permanent transmissible change in DNA sequence. It can be an insertion
or deletion of genetic information, or an alteration in the original
Organization for Rare Disorders (NORD)
federation of voluntary health organizations dedicated to helping
people with rare diseases and to assisting the organizations that
serve them. Headquarters: P.O. Box 8923, New Fairfield, CT 06812.
Toll-free phone: (800) 999-6673. Or call (203) 746-6518. Fax: (203)
746-6481. Home page: www.pcnet.com/~orphan/
building block of DNA or RNA, consisting of one nitrogenous base,
one phosphate molecule, and one sugar molecule (deoxyribose in DNA,
ribose in RNA).
short string of nucleotides; a single-stranded segment of DNA, often
used as a probe to find a matching sequence of DNA or RNA.
gene that is capable of causing the transformation of normal cells
into cancer cells.
or more amino acids linked together.
occurring variations in DNA sequence. Polymorphisms are useful as
genetic markers because they allow researchers to distinguish between
DNA of different origins.
the gene for a specific trait by comparing the DNA of people who have
that trait to the DNA of relatives who don't have the trait.
segment of DNA that acts as a controlling element in the expression
of a gene. It marks the site of initiation of gene transcription.
molecule composed of amino acids linked together in a particular order
specified by a gene's DNA sequence. Proteins perform a wide variety
of functions in the cell; these include serving as enzymes, structural
components, or signaling molecules.
normal gene that can be altered (either through mutation or through
nearby insertion of viral DNA) to become an active oncogene.
to a characteristic that is apparent only when two copies of the gene
encoding it are present--one from the mother and one from the father.
for cutting apart, splicing together, and producing pieces of DNA
from different sources.
fragment length polymorphism (RFLP)
variation in DNA sequence that is easily recognized because it occurs
at a site where a restriction enzyme cuts a specific sequence, producing
DNA fragments of varying lengths. RFLP's often serve as genetic markers.
single-stranded nucleic acid (similar to the double-stranded nucleic
acid DNA) that contains the sugar ribose (DNA contains deoxyribose).
There are many forms of RNA, including messenger RNA, transfer RNA,
and ribosomal RNA (all involved in protein synthesis).
of the chromosomes (X or Y) involved in sex determination. Normal
human females have two X chromosomes in each cell, while normal males
have one X and one Y.
genetic disease in which the hemoglobin protein is mutated, giving
red blood cells a twisted shape that may painfully block circulation.
This often leads to medical crises and may cause an early death. The
recessive disease occurs in children who have inherited the mutated
gene from both their parents, mostly among people of African or Mediterranean
normally exists in two complementary strands that form a double helix,
but it can be separated into two strands of single-stranded DNA. Separation
becomes necessary when genes are being transcribed or when DNA is
replicated prior to cell division.
multicellular organisms, a cell of the soma, or tissues, as opposed
to a cell of the germ line, or sex cell.
that have a foreign gene introduced into their cells.
gene that helps prevent the transformation of normal cells into cancer
cells. When both copies of a tumor-suppressor gene are mutated in
a cell, however, the lack of suppression may lead to the development
of the chromosomes involved in sex determination. Normal human females
have two X chromosomes in each somatic cell, while normal males have
one X and one Y chromosome in each somatic cell. X-linked--Refers
to any gene found on the X chromosome or traits determined by such
genes. Refers also to the specific mode of inheritance of such genes.
of the chromosomes involved in sex determination. Normal human males
carry one X chromosome and one Y chromosome in each somatic cell,
while normal females have two X chromosomes in each somatic cell.