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A | B | C |
D | E | F | G | H
| I | J | K
| L | M | N
| O | P | Q
| R | S | T
| U | V | W
| X | Y | Z
A
 Allele
- An alternate form of a gene. Variations in hair color and
other inherited characteristics are due to different alleles.
Amino acid - any of a class of 20 molecules that are combined
to form proteins. The amino acid sequence of a protein is determined
by the genetic code, specifically by codons , groups of three nucleotide
base pairs that spell out individual amino acids.
Amplification - the production of additional copies of a
specific DNA fragment using methods such as cloning or polymerase
chain reaction (PCR).
Annealing - the pairing of complementary DNA or RNA nucleotides
to form a double-stranded molecule.
Assembly - the process of putting thousands of individual
DNA sequences back together in the proper order using computer and
manual techniques. This part of the sequencing process is much like
solving a puzzle. Researchers use bits of overlapping sequence
to link individual fragments and rebuild the whole, be it a specific
BAC clone, or an entire genome.
Autosome - A non-sex-determining chromosome. Cells
have 22 pairs of autosomes and a pair of sex-determining chromosomes.
B
Bacterial Artificial Chromosome (BAC) - a vehicle based
on the bacteria E. coli that is used to copy, or clone, fragments
of DNA that are 150,000 to 180,000 base pairs (bp) long. These
DNA fragments are used as starting material for DNA sequencing.
Base pair (bp) - two complementary building blocks in DNA
or RNA. The chemicals adenine (A) and thymine (T) bond to
make one of two types of base pairs in DNA, cytosine (C) and guanine
(G) bond to make the other. There are approximately 3 billion base
pairs in the human genome.
C
Carrier - A person who has both a recessive mutated
gene and a normal form of that gene. Carriers don't usually
develop the disease associated with the gene mutation, but
they can pass the mutation on to their children.
Cell - The basic subunit of living organisms. The
body has trillions of cells, each containing two sets of 23
single chromosomes, one inherited from each parent.
Chromosome - A structure in the nucleus of a cell
that contains genes. Normal human cells have 46 chromosomes,
which are arranged in pairs.
Clone - a group of identical molecules, cells, genes, or
organisms that come from a single ancestral parent.
Cloning vector - any vehicle, such as a virus or a BAC,
into which foreign DNA can be inserted for the purpose of replicating
or "cloning" large quantities.
Codon - three nucleotide base pairs, together called a
"triplet," whose order or sequence spells out a unique amino acid
or a termination signal.
Consensus sequence - represents an idealized sequence in
which the position of each DNA base pair represents the order most
often found when many actual sequences are compared.
Contig - a group of BACs or fragments of DNA sequences that
represent contiguous, overlapping regions of the genome.
Cytoplasm - the substance in a cell outside the nucleus.
D
Denaturation - the conversion of DNA molecules from a double-stranded
to a single-stranded state, most often accomplished by heating.
Divergence - the percent difference in nucleotide sequence
between two related DNA sequences, or the percent difference in
amino acid sequence between two related proteins.
DNA (Deoxyribonucleic Acid) - A large molecule with
the complete set of instructions for making all the proteins
a cell needs. DNA consists of two spiraling strands of millions
of chemical building blocks or base pairs. DNA is the
genetic blueprint that determines such features as body height and
skin color and allows the transmission of genetic information
from one generation to the next.
DNA Sequencing - Determining the order of the
base pairs in a segment of DNA.
Dominant Allele - Aform or mutation of a gene
that will produce a trait or disease if a copy is inherited
from just one parent.
E - F
Enzyme - A protein that helps make a specific chemical
reaction occur.
Exon - the parts of the DNA sequence that code for proteins.
Compare with intron.
Expressed sequence tag (EST) - tags of expressed sequence
that can be used as landmarks along the human genome and to provide
clues about the location of new and similar genes.
Fingerprint - the technique of identifying or confirming
specific DNA fragments by "cutting" them with special
enzymes, observing the unique pattern of the fragment sizes that
result, and then comparing with the pattern of a known DNA fragment.
Functional genomics - The science of understanding the orgaization
of genetic pathways and the expression of genes.
G
Gene - the fundamental physical and functional unit of heredity.
A gene is an ordered sequence of nucleotides located in specific
location on a chromosome that encodes the instructions for a specific
functional product, i.e., a protein or an RNA molecule.
Gene Expression - Physical evidence that a gene
has been "turned on" or activated. Gene mapping--determining
the positions of genes on a chromosome.
Gene Marker - Landmarks or signposts
for a particular gene, such as a disease-causing gene. These
can be detectable traits inherited along with the gene or
distinct segments of DNA. Markers can be used to predict the
presence of disease-causing genes.
Gene Therapy - Treating disease by replacing,
altering, or supplementing genes that are defective, missing,
or not functioning.
Genetics - The study of heredity, focusing on how
particular qualities or traits are transmitted from parents
to children.
Genome - The total genetic material in the chromosomes
of an organism. The goal of the Human Genome Project is to
locate and identify the 100,000 genes on the 46 human chromosomes.
Genotype - A person's genetic makeup for one specific
trait. The physical characteristics, such as having blue eyes,
which the genotype codes for is called the phenotype. Genotypes
are generally noted by a series of letters, such as ff, Ff and FF.
FF annotates someone who inherited two genes that code for the F
characteristic (e.g. brown eyes). Ff genotypes have inherited one
of each type of gene from their parents (e.g. a gene for blue eyes
and a gene for brown eyes. Since the brown gene is "dominant"
for eye color, the person will have brown eyes). Similarly, the
person with the ff genotype inherits a "little f" gene
from each parent. The total sum of your individuaql genotypes determines
everything from your eye color to how well you absorb the calcium
in your diet.
Germ Cells - Reproductive cells, such as egg
or sperm cells.
H - L
Homology - similarity in nucleotide or protein sequence
between two individuals within the same species, or among different
species.
Human Genome Project - An international effort begun
in 1990 to locate and identify the 100,000 genes on the 46
human chromosomes.
Hybridization - the process of joining two complementary
strands of DNA, or DNA with a complementary RNA strand, to form
a double-stranded molecule.
Informatics - the field of computer manipulation of scientific
or medical data. As it relates DNA sequencing, informatics is the
part of the process that uses computer programs to capture, analyze,
and transport sequencing data for the appropriate processing and
analysis.
Intron - the parts of the DNA sequence that interrupt the
protein coding sequence, therefore often referred to as "non-coding
regions." This part of the DNA sequence is transcribed
into RNA, but cut out before the protein sequence is translated.
Kilobase (kb) - a measure of length for DNA and RNA equal
to 1,000 bases in single stranded molecules or 1,000 base pairs
in double-stranded molecules.
M
Marker - See " Gene Marker"
Megabase (Mb) - a measure of length for DNA and RNA equal
to one million bases in single stranded molecules, or one million
base pairs in double-stranded molecules.
Mitosis - The process of self-replication by a cell.
During this stage of a normal cell's life cycle, the parent
cell divides into two identical cells.
Molecule - The smallest physical unit of a chemical
substance.
mRNA (messenger RNA) - Acts as the blueprint for making
specific proteins. When the body needs to make a protein, it signals
the DNA found inside the nucleus of the cell to "unzip"
itself at the segment that codes for the desired protein. The unzipped
DNA segment is then copied, producing strands of mRNA.. Once
complete, the DNA rezips itself and the newly created mRNA leaves
the nucleus of the cell and enters the cytoplasm, where another
cell structure called the mitchondria reads the code and assembles
the specified protein.
Mutation - A change in genetic material, such as the
number, arrangement, or molecular sequence of a gene.
N - O
Nucleotide - a subunit of a DNA or RNA molecule that is
made up of a DNA or RNA nitrogenous base (A,T, C, G, U), plus a
phosphate molecule and a sugar molecule, which together provide
the backbone of the "ladder" in the double helix structure.
Nucleus - The part of the cell that contains the chromosomes.
Oncogenes - Genes normally involved in cell growth.
If they are mutated or overexpressed, they can promote the
growth of cancer.
P - Q
PCR (polymerase chain reaction) - a technique for replicating
DNA or RNA in vast quantities (> 1,000,000 copies). It
involves cycles of heating (denaturization) and cooling (annealing)
of a nucleotide template, or primer, in the presence of random,
single, nucleotides and special enzymes, which allow them to be
incorporated into replicated fragments in the proper order.
The copies can be used for paternity testing, screening for
genetic diseases, and other scientific analysis.
Penetrance - The probability that a particular gene
mutation will produce the disease.
Phage - a type of virus whose host organism is a bacteria.
At the BCM-HGSC, M13 phage are used to clone, or replicate, small
fragments of DNA for making shotgun libraries to be used in DNA
sequencing.
Phenotype - The observable expression of a genetically
determined trait. The trait may
be visibly apparent, such as hair color, or detectable with
a laboratory test, such as blood type.
Physical map - a map of identifiable DNA landmarks that
are not related to inheritance, such as known genes and restriction
enzyme cutting sites. Distance on the physical map is measured
in base pairs. The lowest resolution physical map is the banding
pattern on the 24 different chromosomes. The highest resolution
physical map is the complete nucleotide sequence.
Prenatal Diagnosis - Examining fetal cells from
the amniotic fluid, the placenta, or fetal blood for alterations
in the genes or chromosomes before birth.
Primer - short pre-existing nucleotide chain to which new
nucleotides can be added by DNA enzymes known as "polymerases"
using PCR techniques.
Probe - A length of single-stranded DNA that matches
part of a gene that has already been identified. If the DNA
probe is made from a mutated gene, it can be used to determine
whether someone has that genetic defect. The probe will bind
to complementary parts of the patient's gene.
Proteins - Large, complex molecules made from amino acids.
Protein is needed for the structure, function, and regulation
of the body. The "contracting" components of muscle
cells are proteins, as are hormones, enzymes, and antibodies.
Proteomics - The scientific study of the funcition of specific
proteins in body cells.
R
Recessive Allele - A form or mutation of a gene
that must be inherited from both parents to produce a trait
or disease.
Reverse transcription - the synthesis of new strands of
DNA using an RNA template and an enzyme called "reverse transcriptase."
RNA (Ribonucleic Acid) - A chemical similar to DNA
from which proteins are made. Unlike DNA, RNA can leave the
nucleus of the cell.
S
Sequence-Draft - a first-pass version of the human genome
sequence, which is expected to be approximately 90% complete.
This means that the draft sequence will have gaps in the sequence
data and regions that contain errors or are out of order.
However, the value of the draft sequence is its immediate availability
for researchers worldwide. Despite such ambiguities, such
draft sequence information will still have high utility for many
researchers.
Sequence-Finished - a finalized version of the human genome
sequence. The finished sequence will be completed to pre-defined
quality standards, known as the "Bermuda standard," which ensures
100% completion of the genome sequence with an error rate of less
than one incorrect base pair in 10,000.
Sequence tagged site (STS) - short DNA sequence (200-500
bp) that has a single occurrence in the human genome with known
location and sequence. STSs can be detected by PCR methods
and are useful as landmarks on the genome, to localize and orient
sequence data.
Sequencing - determination of the order of the nucleotides
(or base pairs) in a DNA or RNA molecule, or the order of amino
acids in a protein.
Shotgun sequencing - a sequencing approach that involves
the cloning of a large region of DNA (whole BAC to whole genome)
into many smaller fragments of DNA, which are then sequenced individually
and reassembled to recreate the starting material.
Stem Cells - Unspecialized, immature cells in
the bone marrow from which all types of blood cells originate.
Suicide Gene - A gene that causes the cell to
produce an enzyme that will attract a lethal drug. Suicide
genes are used in gene therapy as a way to target medication
toward cells associated with a particular disease.
T - W
Transcription - The process of copying information
from DNA into new strands of messenger RNA (mRNA), which then
carries the information to the cytoplasm to serve as a blueprint
for manufacturing a specific protein.
Translation - the synthesis of a protein from a "messenger
RNA" template. The mRNA template spells out the order
of amino acids in the protein to be made via the nucleotide "triplets"
or codons.
Tumor-Suppressor Genes - Genes that normally
restrain cell growth. If they are defective or missing, cancer
can develop because cells can grow uncontrollably.
Vector - A "vehicle", such as a modified
virus or DNA molecule, used to deliver genetic material into
the body for gene therapy.
X - Z
X Chromosome - A sex chromosome. Normal females
carry two X chromosomes.
Y Chromosome - A sex chromosome. Normal males
carry one Y chromosome and one X chromosome.
--Glossary and photo courtesy of Baylor
College of Medicine Office of Public Affairs.
 More
about the Human Genome From Baylor College of Medicine
Office of Public Affairs.
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