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A Glossary of Technical Genetic Terms

Collected by OGBub and edited by J.Cannabis.

Algorithm: In computational terminology, a programme designed to perform
a specific calculation or problem-solving function.

Allele: An alternative form of a gene at the same chromosomal locus.

Amino acid: The constituent subunits of proteins. Amino acids polymerize
to form linear chains linked by peptide bonds; such chains are
termed polypeptides. There are twenty naturally occurring amino
acids of which all proteins are made.

Antibody: A protein produced by the immune system in response to an
antigen (a molecule that is perceived to be foreign). Antibodies bind
specifically to their target antigen to help the immune system destroy
the foreign entity.

Autosome: Any chromosome other than a sex chromosome.

Base: See nucleotide base

Bacterial artificial chromosome (BAC): DNA vectors into which large
DNA fragments can be inserted and cloned in a bacterial host.

Bioinformatics: The discipline encompassing the development and utilization
of computational facilities to store, analyse and interpret biological

Biotechnology: The industrial application of biological processes, particularly
recombinant DNA technology and genetic engineering.

Blastocyst: The mammalian embryo at the stage at which it is implanted
into the wall of the uterus.

Carrier: A person who is heterozygous, that is carries one allele, for a
recessive disease, and hence does not display the disease phenotype
but can pass it on to the next generation.

Cell Cycle: The term given to the series of tightly regulated steps that a
cell goes through between its creation and its division to form two
daughter cells.

Chromosome: Subcellular structures which convey the genetic material
of an organism.

Clone: A line of cells derived from a single cell and therefore carrying
identical genetic material.

Cloning vector: A small circle of DNA (plasmid) or modified bacteriophage
(bacterial virus) that can carry a segment of foreign DNA into
an appropriate host organism (e.g. a bacterial, yeast or mammalian
cell). Used to amplify the amount of foreign DNA or for generating
its protein product.

Comparative genomics: The comparison of genome structure and function
across different species in order to further understanding of biological
mechanisms and evolutionary processes.

Complementary DNA (cDNA): DNA generated from an expressed messenger
RNA through a process known as reverse transcription.

Congenital: Any trait, condition or disorder that exists from birth.

Cytoplasm: The internal matrix of a cell. The cytoplasm is the area
between the outer periphery of a cell (the cell membrane) and the
nucleus (in a eukaryotic cell).

Demographic transition: As used in this Report, the change in a society
from extreme poverty to a stronger economy, often associated by a
transition in the pattern of diseases from malnutrition and infection
to the intractable conditions of middle and old age, cardiovascular
disease, diabetes, and cancer, for example.

DNA (deoxyribonucleic acid): The chemical that comprises the genetic
material of all cellular organisms.

DNA cloning: Replication of DNA sequences ligated into a suitable vector
in an appropriate host organism (see also Cloning vector).

DNA sequencing: Technologies through which the order of base pairs in
a DNA molecule can be determined.

Dominant: An allele is described as dominant if it exerts its phenotypic
effect when present in the heterozygous state.

Enzyme: An enzyme is a biological catalyst: a protein which controls the
rate of a biochemical reaction within a cell.

Eukaryote: An organism whose cells show internal compartmentalization
in the form of membrane-bounded organelles (includes animals,
plants, fungi and algae).

Exon: The sections of a gene that code for all of its functional product.
Eukaryotic genes may contain many exons interspersed with non-coding

Expressed sequence tag (EST): Partial or full complementary DNA
sequences which can serve as markers for regions of the genome
which encode expressed products.

Founder effect: Changes in allelic frequencies that occur when a small
group is separated from a large population and establishes a colony
in a new location.

Functional genomics: The development and implementation of technologies
to characterize the mechanisms through which genes and their
products function and interact with each other and with the environment.

Gene: The fundamental unit of heredity. In molecular terms, a gene comprises
a length of DNA that encodes a functional product, which may
be a polypeptide (a whole or constituent part of a protein) or a
ribonucleic acid.

Genetics: The study of heredity.

Gene expression: The process through which a gene is activated at particular
time and place so that its functional product is produced.

Gene therapy: The introduction of genetic material into an individual, or
the modification of the individual’s genetic material, in order to
achieve a therapeutic objective.

Genetic code: The relationship between the order of nucleotide bases in
the coding region of a gene and the order of amino acids in the
polypeptide product. It is a universal, triplet, non-overlapping code
such that each set of three bases (termed a codon) specifies which of
the 20 amino acids is present in the polypeptide chain product at a
particular position.

Genetic counselling: A process through which patients who are at risk
from genetic disease are provided with accurate information about a
particular genetic test and the implications of the results in a nondirective

Genetic epidemiology: A field of research in which correlations are
sought between phenotypic trends and genetic variation across population

Genetic map: A map showing the positions of genetic markers along the
length of a chromosome relative to each other (genetic map) or in
absolute distances from each other (physical map).

Genetic susceptibility: Predisposition to a particular disease due to the
presence of a specific allele or combination of alleles in an individual’s

Genome: The sum total of the genetic material present in a particular
organism. This includes both the DNA present in the chromosomes
and that in subcellular organelles (e.g. mitochondria or chloroplasts).
It also includes the RNA genomes of some viruses.

Genome annotation: The process through which landmarks in a genomic
sequence are characterized through computational and other means
— for example, genes are identified, predictions made as to the function
of their products, their regulatory regions defined and intergenic
regions characterized.

Genomics: The study of the genome and its action.

Genotype: The total genetic constitution of an organism.

Germ-line cells: A cell with a haploid chromosome content (also referred
to as a gamete); in animals, sperm or egg, in plants, pollen or ovum.

Haemoglobin: The molecule in red blood cells which transports oxygen
from the lungs to body tissues.

Haplotype: A series of closely linked loci on a chromosome which tend
to be inherited together as a block.

Heterozygote: With respect to a particular gene at a defined chromosomal
locus, a heterozygote has a different allelic form of the gene on
each of the two homologous chromosomes.

Homozygote: With respect to a particular gene at a defined chromosomal
locus, a homozygote has the same allelic form of the gene on
each of the two homologous chromosomes.

Hormone: A molecule secreted by a cell or tissue in an organism, which
has a functional consequence in other cells located remotely.

Human Genome Project: A programme to determine the sequence of the
entire three billion (3×109) bases of the human genome.

Intron: A non-coding sequence within eukaryotic genes which separates
the exons (coding regions). Introns are spliced out of the messenger
RNA molecule created from a gene after transcription, prior to translation
(protein synthesis).

Knock-out: A technique used primarily in mouse genetics to inactivate a
particular gene in order to define its function.

Library: A collection of genomic or complementary DNA sequences
from a particular organism that have been cloned in a vector and
grown in an appropriate host organism (e.g. bacteria, yeast).

Linkage: The phenomenon whereby pairs of genes which are located in
close proximity on the same chromosome tend to be co-inherited

Locus: The specific site on a chromosome at which a particular gene or
other DNA landmark is located.

Marker: A specific feature at an identified physical location on a chromosome,
whose inheritance can be followed. The position of a gene
implicated in a particular phenotypic effect can be defined through its
linkage to such markers.

Meiosis: A process of two successive cell divisions which results in the
production of four daughter cells which each contain half the quantity
of chromosomal material present in the parent cell. This form of
cell division is used to produce gametes in sexually reproducing

Mendelian inheritance: The pattern of heritability of a particular phenotypic
trait that follows the laws of inheritance developed by Mendel. Monogenic disorders
or traits show Mendelian inheritance.

Microarray: A grid of nucleic acid molecules of known composition
linked to a solid substrate, which can be probed with total messenger
RNA from a cell or tissue to reveal changes in gene expression relative
to a control sample. Microarray technology, which is also known
as “DNA chip” technology, allows the expression of many thousands
of genes to be assessed in a single experiment.

Mitochondria: Cellular organelles present in eukaryotic organisms which
enable aerobic respiration, which generates the energy to drive cellular
processes. Each mitochondria contains a small amount of DNA
encoding a small number of genes (approximately 50).

Mitosis: Standard cell division through which a cell divides to produce
two daughter cells with identical chromosomal complement to the
parent cell.

Model organism: An experimental organism in which a particular physiological
process or disease has similar characteristics to the corresponding
process in humans, permitting the investigation of the common
underlying mechanisms. Models for human diseases (particularly
in mice) have been identified through naturally occurring mutations
and can be created using sophisticated transgenics technologies.

Molecular biology: The study of biological processes at the molecular

Monogenic disease: A disease whose pathology results from the presence
of a particular allele of a gene, either in a heterozygous or homozygous

Multifactorial (multigenic) disease: A disease whose pathology is
dependent on the complex interplay of several genetic and environmental

Mutation: A structural change in a DNA sequence resulting from uncorrected
errors during DNA replication.

Nucleotide (nucleotide base): Nucleotides are the subunits from which
DNA and RNA molecules are assembled. A nucleotide is a base molecule
(i.e. adenine, cytosine, guanine and thymine in the case of DNA),
linked to a sugar molecule and phosphate groups.

Oncogene: An acquired mutant form of a gene which acts to transform a
normal cell into a cancerous one.

Pharmacogenomics: The identification of the genes which influence individual
variation in the efficacy or toxicity of therapeutic agents, and
the application of this information in clinical practice.

Phenotype: The observable characteristics of an organism.

Physical map: A map showing the absolute distances between genes (see
gene mapping).

Plasmid: Circular extra-chromosomal DNA molecules present in bacteria
and yeast. Plasmids replicate autonomously each time a bacterium
divides and are transmitted to the daughter cells. DNA segments are
commonly cloned using plasmid vectors.

Polymerase chain reaction (PCR): A molecular biology technique developed
in the mid-1980s through which specific DNA segments may be
amplified selectively.

Polymorphism: The stable existence of two or more variant allelic forms
of a gene within a particular population, or among different populations.

Positional cloning: The technique through which candidate genes are
located in the genome through their co-inheritance with linked markers.
It allows genes to be identified for which there is no information
regarding the biochemical action of their functional product.

Post-transcriptional modification: A series of steps through which protein
molecules are biochemically modified within a cell following
their synthesis by translation of messenger RNA. A protein may
undergo a complex series of modifications in different cellular compartments
before its final functional form is produced.

Prenatal diagnosis: Clinical diagnostic techniques to genetically test a
developing fetus.

Prokaryote: An organism or cell lacking a nucleus and other membrane
bounded organelles. Bacteria are prokaryotic organisms.

Protein: Proteins are biological effector molecules encoded by an organism’s
genome. A protein consists of one or more polypeptide chains
of amino acid subunits. The functional action of a protein depends on
its three dimensional structure, which is determined by its amino acid

Proteomics: The development and application of techniques to investigate
the protein products of the genome and how they interact to
determine biological functions.

Recessive: An allele is described as recessive if it has no phenotypic effect
in the heterozygous state.

Recombinant DNA technology: The term given to some techniques of
molecular biology and genetic engineering which were developed in
the early 1970s. In particular, the use of restriction enzymes, which
cleave DNA at specific sites, allow sections of DNA molecules to be
inserted into plasmid or other vectors and cloned in an appropriate
host organism (e.g. a bacterial or yeast cell).

Regulatory sequence: A DNA sequence to which specific proteins bind
to activate or repress the expression of a gene.

Reproductive cloning: Techniques aimed at the generation of an organism
with an identical genome to an existing organism.

Restriction enzymes: A family of enzymes derived from bacteria that cut
DNA at specific sequences of bases.

Ribosome: Subcellular structures which form the catalytic site of protein
synthesis. Ribosomes comprise protein and RNA complexes at which
amino acid chains are constructed as directed by the sequence of messenger
RNA molecules.

RNA (ribonucleic acid): A single stranded nucleic acid molecule comprising
a linear chain made up from four nucleotide subunits (A, C, G
and U). There are three types of RNA: messenger, transfer and ribosomal.

Sex chromosome: The pair of chromosomes that determines the sex of
an organism. There are two sex chromosomes, X and Y. In the vast
majority of organisms, males possess an X and a Y chromosome and
females two X chromosomes.

Shotgun sequencing: A cloning method in which total genomic DNA is
randomly sheared and the fragments ligated into a cloning vector.
Sometimes referred to as “shotgun” cloning.

Signal transduction: The molecular pathways through which a cell senses
changes in its external environment and changes its gene expression
patterns in response.

Single nucleotide polymorphism (SNP): A chromosomal locus at which a
single base variation exists stably within populations (typically
defined as each variant form being present in at least 1-2% of individuals).

Splicing: The process through which introns are removed from a messenger
RNA prior to translation and the exons adjoined.

Stem cell: A cell which has the potential to differentiate into a variety of
different cell types depending on the environmental stimuli it receives.

Synteny: Syntenic genes are genes which reside on the same chromosome.

Telomere: The natural end of a chromosome.
Therapeutic cloning: The generation and manipulation of stem cells with
the objective of deriving cells of a particular organ or tissue to treat a

Transcription: The process through which a gene is expressed to generate
a complementary messenger RNA molecule.

Transcriptome: The total messenger RNA expressed in a cell or tissue at
a given point in time.

Transgene: A gene from one source that has been incorporated int the
genome of another organism.

Transgenic animal/plant: A fertile animal or plant that carries an introduced
gene(s) in its germ-line.

Translation: The process through which a polypeptide chain of amino
acid molecules is generated as directed by the sequence of a particular
messenger RNA sequence.

Transposon: A mobile nucleic acid element.

Tumour suppressor gene: A gene which serves to protect cells from
entering a cancerous state. According to Knudson’s “two-hit”
hypothesis, both alleles of a particular tumour suppressor gene must
acquire a mutation before the cell will enter a transformed state.

Vector: See Cloning vector.

Yeast two-hybrid system: A genetic method for analysing the interactions
of proteins.