|
|
Glossary
A | B |
C | D |
E | F |
G | H |
I |
K |
M | N |
P | R |
S | T
A
Adenine -- One of the four bases
that make up the letters ATGC in DNA. Adenine ("A") always
pairs with thymine ("T").
Allele -- One of many possible
forms of a given gene. Different alleles produce variation
in inherited characteristics such as hair and eye color. In
an individual, one form of an allele may be expressed
(dominant) while the other form may be masked
(recessive).
Amino acids -- There are 20
different amino acids, which are often called the "building
blocks" of proteins. Amino acids link together in long
chains to form proteins in the body.
Antibody -- A blood protein
produced in response to an antigen (any substance capable of
producing antibodies) in the body. Antibodies bind to
antigens, often produced by disease, and help the body fight
against them. Antibodies can help the body to develop
immunity to a disease.
Antisense -- A strand of DNA that
is not responsible for coding. The antisense strand serves
as the template for RNA synthesis.
Autosome -- Any chromosome other
than a sex chromosome. Humans have 22 pairs of autosomes.
B
Base pair -- A pair of bases, or
molecules (either adenine and thymine or cytosine and
guanine), which forms one rung in the DNA ladder. Bases are
the letters that spell out genetic code.
Birth defect -- A physically or
mentally disabling condition present in an individual at
birth. There are more than 4,000 known birth defects, some
of which are fatal. A birth defect may be caused by a faulty
gene or by environmental factors during pregnancy, such as
radiation exposure.
BRCA1/BRCA2 -- Two mutant genes
that are responsible for approximately 50 percent of all
inherited forms of breast cancer. Normally these genes are
tumor suppressors, which limit the growth of tumors. When
mutated, these genes fail to do their job correctly,
allowing cancers to grow.
C
Carrier -- A person who possesses
one copy of a mutant allele that can cause disease when
paired with another mutant allele. Carriers do not have the
disease they carry but can give the disease to a child if
the other parent is also a carrier.
Centromere -- The middle portion
of a chromosome where two sister chromatids (chromosome
strands) join together.
Chromosome -- A DNA molecule
containing genes and found in the nucleus of a cell. Humans
have 23 pairs of chromosomes (46 in all). Forty-four of our
chromosomes are autosomes and the remaining two are sex
cells. Other animals have different numbers of chromosomes.
Every child gets half of his or her chromosomes from the
father and half from the mother.
Cloning -- The process of copying
a specific piece of DNA. Geneticists use cloning in their
research to study genetic structure and function.
Codon -- A sequence of three bases
in DNA or RNA that specifies an amino acid or a stop signal
in protein synthesis.
Congenital -- Any trait or
condition that exists from birth.
Cystic fibrosis -- A hereditary
disease in which the primary symptoms are breathing
difficulties and respiratory infections due to an
accumulation of mucus in the lungs. The symptoms of this
disease usually develop in infancy.
Cytosine -- One of the four bases
that make up the letters ATGC in DNA. Cytosine ("C") always
pairs with guanine ("G").
D
Deletion -- A kind of genetic
mutation that results when a chromosome loses a piece of
DNA, leading to disease or other abnormalities.
Deoxyribonucleic acid (DNA) -- The
chemical found in the nucleus of the cell that holds the
genetic instructions for making all living organisms.
Diploid -- The number of
chromosomes in most human cells, except sex cells. This
number is 46.
DNA - The chemical inside the
nucleus of a cell that carries the genetic instructions for
making living organisms.
DNA chip -- A part of the
microarray technology scientists use in gene sequencing to
understand how the thousands of genes in a genome interact
simultaneously.
DNA replication -- The process by
which the DNA molecule unwinds and makes an exact copy of
itself.
DNA sequencing -- The process by
which scientists determine the exact order of the base pairs
in a segment of DNA.
Dominant -- A gene that almost
always results in the expression of a certain characteristic
in an individual, even though an individual's genome only
possesses one copy of the gene. This gene always has a 50-50
chance of being passed on to a child.
Double helix -- The twisted ladder
structure of the DNA molecule. The sides of the ladder are
made of sugar and phosphate molecules; the rungs consist of
nucleotide bases joined by hydrogen bonds.
Duplication -- A type of mutation
that occurs when one or more copies is made from any piece
of DNA, a gene, or a chromosome.
E
Enzyme -- A protein that
encourages biochemical reactions. Missing or abnormal
enzymes can result in diseases and abnormalities.
Exon -- The part of a gene that
contains the code for producing the gene's protein. In
humans, exons are often separated by long regions of DNA
called introns, or "junk DNA," that have no apparent
function.
F
Fragile X syndrome -- A frequent
genetic cause of mental retardation. A mutation causes a
repetition of the letters CGG in a gene on the X chromosome.
The more repeats of this code on a person's X chromosome,
the more impaired he or she is likely to be.
G
Gene -- Pieces of DNA passed from
parent to offspring that contain hereditary information.
Gene mapping -- The process of
determining the position of each gene on a chromosome and
the distance between them.
Genetic code -- The genetic
instructions -- A, T, G, and C -- that combine in different
three-letter "words," specifying which amino acids are
needed to make every protein in the body.
Genetic screening -- Tests
administered to a specific segment of the population that is
at high risk for carrying a certain genetic disorder.
Genome -- All the DNA contained in
an organism.
Genotype -- Genetic information
that does not show outward characteristics.
Guanine -- One of the four bases
that make up the letters ATGC in DNA. Guanine ("G") always
pairs with cytosine ("C").
H
Haploid -- Half the diploid number
of chromosomes in sperm or egg cells (23 cells).
I
Intron -- A sequence of DNA that
does not code. Introns are sometimes called "junk DNA."
K
Knockout -- The process by which
genes are made inactive in a laboratory. Scientists often
use knockouts in mice in order to study what effect the
inactivity of a given gene will have on the animal.
M
Messenger RNA (mRNA) -- The
template for protein synthesis. Each set of three bases, or
codons, in mRNA orders the production of a certain protein.
The structure of mRNA is the same as one strand of DNA.
N
Non-coding DNA -- One of the two
identical strands that make up the DNA double helix. The
non-coding strand, or antisense strand, is a mirror-image of
the coding strand, but does not carry the information needed
to order the production of proteins.
Nonsense mutation -- A
substitution of one of the bases of DNA that results in a
stop codon.
Nucleotide -- One of the building
blocks of DNA and RNA. A nucleotide is comprised of one base
(either adenine, guanine, cytosine, and thymine), one
molecule of sugar, and one molecule of phosphoric acid.
Nucleus -- The structure in the
center of each cell that holds chromosomes.
P
p53 -- A gene responsible for
regulating the growth cycle of a cell. A mutation to this
gene can cause certain types of cancer.
Phenotype -- Traits, such as hair
and eye color and disease, that are observable externally.
These traits are not always inherited.
Polydactyly -- A genetic
abnormality that causes a person to be born with more than
ten fingers and/or toes.
Protease -- A protein that digests
other proteins.
Protein -- A large, complex
molecule made up of one or more amino acid chains. Proteins
are responsible for many activities at the cellular level.
R
Recessive -- A trait or disorder
that appears only in a child who has received two copies of
the same mutant gene, one from each parent.
Repressor -- A protein that
regulates a gene by turning it off.
Ribonucleic acid (RNA) -- A
chemical that is very similar to one strand of the DNA
double helix. RNA delivers important genetic messages to the
cytoplasm of cells, where proteins are made. In RNA, the
letter "U" replaces the letter "T" in DNA ("U" stands for
Uracil).
S
Sex chromosome -- One of the two
chromosomes that specify an individual's sex. Humans have
two sex chromosomes (X and Y). Females have two X
chromosomes and males have one X chromosome and one Y.
Sex-linked -- Located on the X
chromosome. Sex-linked diseases are only seen in men.
T
Tay-Sachs -- An incurable
recessive genetic disorder that usually develops within the
first year of a child's life, causing the build-up of fat
deposits in the brain. Children born with Tay-Sachs die
before the age of ten.
Thymine -- One of the four bases
that make up the letters ATGC in DNA. Thymine ("T") always
pairs with adenine ("A").
Note: This glossary is adapted, with permission, from the
National Human Genome Resource Institute's "Glossary of
Genetic Terms." To visit the full glossary, visit the
NHGRI Web site, listed in the
Resources
section.
Watch the Program Here
|
Our Genetic Future (A Survey)
Manipulating Genes: How Much is Too Much?
|
Understanding Heredity
Explore a Stretch of Code
|
Nature vs Nurture Revisited
Sequence for Yourself
|
Journey into DNA |
Meet the Decoders
Resources
|
Update to Program
|
Teacher's Guide
|
Transcript
Site Map
|
Cracking the Code of Life Home
Editor's Picks
|
Previous Sites
|
Join Us/E-mail
|
TV/Web Schedule
|
About NOVA
Watch NOVAs online
|
Teachers |
Site Map
|
Shop
|
Search |
To Print
PBS Online |
NOVA Online |
WGBH
©
| Updated April 2001
|
|
|