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gene changes that arise within individual cells and
accumulate throughout a person's lifetime; also called
somatic mutations. (See Hereditary mutation.)
variant forms of the same gene. Different alleles produce
variations in inherited characteristics such as eye
color or blood type.
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
any of a class of 20 molecules that combine to form
proteins in living things.
Amyotrophic lateral sclerosis:
an inherited, fatal degenerative nerve disorder; also
known as Lou Gehrig's disease.
any of the non-sex-determining chromosomes. Human cells
have 22 pairs of autosomes.
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 gene that normally helps to restrain cell growth.
BRCA1 breast cancer susceptibility gene:
a mutated version of BRCA1, which predisposes a person
toward developing breast cancer.
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.
small, watery, membrane-bound compartment filled with
chemicals; the basic subunit of any living thing.
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
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.
a group of identical genes, cells, or organisms derived
from a single ancestor.
the process of making genetically identical copies.
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
examination of the colon through a flexible, lighted
instrument called a colonoscope.
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.
an inherited disease in which a thick mucus clogs the
lungs and blocks the ducts of the pancreas.
the cellular substance outside the nucleus in which
the cell's organelles are suspended.
severe impairment of mental functioning.
the substance of heredity; a large molecule that carries
the genetic information that cells need to replicate
and to produce proteins.
DNA repair genes:
certain genes that are part of a DNA repair pathway;
when altered, they permit mutations to pile up throughout
determining the exact order of the base pairs in a
segment of DNA.
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 protein that facilitates a specific chemical reaction.