gene changes that arise within individual cells and accumulate
throughout a person's lifetime; also called somatic mutations. (See
Hereditary mutation.)
a disease that causes memory loss, personality changes, dementia and,
ultimately, death. Not all cases are inherited, but genes have been found
for familial forms of Alzheimer's disease.
the two complementary, nitrogen-rich molecules held together by weak
chemical bonds. Two strands of DNA are held together in the shape of a
double helix by the bonds between their base pairs. (See Chemical base.)
a person who has a recessive mutated gene, together with its normal
allele. Carriers do not usually develop disease but can pass the mutated
gene on to their children.
testing to identify individuals who carry disease-causing recessive
genes that could be inherited by their children. Carrier testing is
designed for healthy people who have no symptoms of disease, but who are
known to be at high risk because of family history.
an essential building block. DNA contains four complementary bases:
adenine, which pairs with thymine, and cytosine, which pairs with guanine.
In RNA, thymine is replaced by uracil.
structures found in the nucleus of a cell, which contain the genes.
Chromosomes come in pairs, and a normal human cell contains 46
chromosomes, 22 pairs of autosomes and two sex chromosomes.
types of physical DNA maps that consist of overlapping segments of DNA
(contigs) that, taken together, completely represent that section of the
genome. (See Physical maps.)
a phenomenon, also known as recombination, that sometimes occurs
during the formation of sperm and egg cells (meiosis); a pair of
chromosomes (one from the mother and the other from the father) break and
trade segments with one another.
a gene that is expressed, regardless of whether its counterpart allele
on the other chromosome is dominant or recessive. Autosomal dominant
disorders are produced by a single mutated dominant allele, even though
its corresponding allele is normal. (See Recessive allele.)
a unit of inheritance; a working subunit of DNA. Each of the body's
50,000 to 100,000 genes contains the code for a specific product,
typically, a protein such as an enzyme.
examining a sample of blood or other body fluid or tissue for
biochemical, chromosomal, or genetic markers that indicate the presence or
absence of genetic disease.
DNA maps that assign relative chromosomal locations to genetic
landmarksѥither genes for known traits or distinctive sequences of DNA -
on the basis of how frequently they are inherited together. (See Physical
maps.)
a gene change in the body's reproductive cells (egg or sperm) that
becomes incorporated in the DNA of every cell in the body; also called
germline mutation. (See Acquired mutations.)
an international research effort (led in the United States by the
National Institutes of Health and the Department of Energy) aimed at
identifying and ordering every base in the human genome.
a biochemical phenomenon that determines, for certain genes, which one
of the pair of alleles, the mother's or the father's, will be active in
that individual.
a gene-hunting technique that traces patterns of heredity in large,
high-risk families, in an attempt to locate a disease-causing gene
mutation by identifying traits that are co-inherited with it.
an inborn error of metabolism caused by the lack of an enzyme,
resulting in abnormally high levels of the amino acid phenylalanine;
untreated, PKU can lead to severe, progressive mental retardation.
DNA maps showing the location of identifiable landmarks, either genes
or distinctive short sequences of DNA. The lowest resolution physical map
shows the banding pattern on the 24 different chromosomes; the highest
resolution map depicts the complete nucleotide sequence of the
chromosomes. (See Contig maps.)
examining fetal cells taken from the amniotic fluid, the primitive
placenta (chorion), or the umbilical cord for biochemical, chromosomal, or
gene alterations.
a specific sequence of single-stranded DNA, typically labeled with a
radioactive atom, which is designed to bind to, and thereby single out, a
particular segment of DNA.
surgery to remove tissue that is in danger of becoming cancerous,
before cancer has the chance to develop. Surgery to remove the breasts of
women at high risk of developing breast cancer is known as prophylactic
mastectomy.
a large, complex molecule composed of amino acids. The sequence of the
amino acidsѡnd thus the function of the proteinѩs determined by the
sequence of the base pairs in the gene that encodes it. Proteins are
essential to the structure, function, and regulation of the body. Examples
are hormones, enzymes, and antibodies.
a gene that is expressed only when its counterpart allele on the
matching chromosome is also recessive (not dominant). Autosomal recessive
disorders develop in persons who receive two copies of the mutant gene,
one from each parent who is a carrier. (See Dominant allele.)
an eye cancer caused by the loss of a pair of tumor-suppressor genes;
the inherited form typically appears in childhood, since one gene is
missing from the time of birth.
an inherited, potentially lethal disease in which a defect in
hemoglobin, the oxygen-carrying pigment in the blood, causes distortion
(sickling) and loss of red blood cells, producing damage to organs
throughout the body.
the process of copying information from DNA into new strands of
messenger RNA (mRNA). The mRNA then carries this information to the
cytoplasm, where it serves as the blueprint for the manufacture of a
specific protein.
the process of turning instructions from mRNA, base by base, into
chains of amino acids that then fold into proteins. This process takes
place in the cytoplasm, on structures called ribosomes.
