GLOSSARY
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General Definitions
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: Short for Adenine - one of the nitrogenous bases occurring in DNA and RNA.
achondroplasia: A genetic disorder, inherited as an autosomal dominant trait, that results in a form of dwarfism characterised by short limbs, a normal sized head and body and normal intelligence. The bones of the arms and legs are smaller than normal due to a defect in both bone and cartilage.
actin: A protein found in muscle that helps bring about muscle contraction.
adenine, A: One of the nitrogenous bases occurring in DNA and RNA.
ADHD (attention deficit hyperactivity disorder): A mental condition, usually seen in children, that leads to excessive activity levels and a marked impairment of attention ability that may affect learning. In some cases children may also exhibit disruptive or aggressive behaviour.
affected sib pair analysis: Genetic analysis based on two siblings affected by a disease. Genetic markers evenly spaced throughout the genome are genotyped. For each locus the sibs could share 0, 1 or 2 alleles with expected ratios of each of these outcomes being 25%, 50% and 25% respectively.
albinism: An inherited condition leading to a lack of normal body pigment (melanin). Albinos characteristically have white hair, and pink skin and eyes.
alcoholism: A physical dependence on alcohol. (A complex chronic psychological and nutritional disorder associated with excessive and usually compulsive drinking of alcohol.)
allele, alleles: One of two or more alternative forms of a gene.
alpha 1 antitrypsin: An inhibitor of the enzyme elastase. People with a deficiency in this protein suffer from breakdown of connective tissue in the lung that lowers the elasticity of the lungs, resulting in the condition called emphysema. Alpha 1 antitrypsin deficiency related emphysema is inherited as an autosomal recessive disorder.
amino acid, amino acids: An organic molecule, forming the basic units of proteins.
amyotrophic sclerosis: hardening of tissue surrounding the lateral columns of the spinal cord and medulla of the brain causing progressive loss of muscle bulk, weakness and paralysis
androgen receptor: a protein molecule on the cell surface or in the cell interior that has an affinity for an androgen (one of a group of steroid hormones that stimulate the development of male sex organs and secondary sex characteristics.)
antagonist: A chemical that acts within the body to reduce the physiological activity of another chemical substance.
anticodon: A three-base sequence on a tRNA molecule, complementary to a three-base sequence in an mRNA molecule, which codes for a particular amino acid.
antigen: Any substance that is recognised by the immune system as foreign or potentially dangerous to the body and against which antibodies are produced. Specific antibodies target different antigens.
atopic: Describing a form of allergy in which there is an inherited tendency to develop hypersensitivity to certain allergens. This includes some forms of hay fever, eczema, asthma and psoriasis.
atopy: A form of allergy in which there is an inherited tendency to develop hypersensitivity to certain allergens. This includes some forms of hay fever, eczema, asthma and psoriasis.
autonomy: Respect for people's ability to think for themselves and to independently make decisions about their own life.
autosomal: describes a trait showing a pattern of segregation characteristic of a gene located on an autosome (not a sex chromosome).
autosome: Any of the chromosomes not involved in sex determination. A human cell has 22 pairs.
BAC: Bacterial Artifical Chromosome
basal cell (skin): one of the innermost cells of the deeper epidermis (outer layer) of the skin
base, bases: Nitrogenous bases are essential building blocks of nucleotides. The bases of two polynucleotide chains link together by weak bonds to form the rungs of the DNA double helix.
beta cells (pancreas): endrocrine cells in the Islets of Langerhans of the pancreas that produce and secrete the hormone insulin. Insulin is secreted in to the blood stream in response to increases in blood sugar and brings about reduction of blood sugar level back to normal.
biopsy: the removal of a small part of tissue from the body for examination and diagnosis of disease.
Caenorhabditis elegans: a small nematode worm, about 1mm long, commonly used as a model organism to study genetics and development.
cancer: Cancer is an abnormal and uncontrolled proliferation of cells that then invade and destroy surrounding tissues.
candidate (gene): a gene mapped to a region known to be linked to a specific disease whose produce has properties suggesting it may be the actual disease-associated gene. (Once a disease gene has been localised to a region containing just a few genes, all of those genes may be, in practice, referred to as candidate genes)
candidate interval: an interval or region on a chromosome possibly containing a disease-causing gene.
carbohydrate: any of a large number of compounds that contain carbon, hydrogen, and oxygen and have the general formula Cx(H2O)y. Examples include sugars, starches, and celluloses. Most are formed by green plants and are obtained by animals via their diet.
carrier: A person who is heterozygous for a condition inherited recessively. This means that they carry one copy of the allele for the disease, but they do not actually have the disease.
cartilage: a dense connective tissue with elastic properties that comprises most of the skeleton of an embryo. Most of this is replaced by bone (ossification) but cartilage remains an important component of some structures that include joints, respiratory passages and the external ear.
cDNA: (complementary DNA)is DNA synthesised to complement the bases in a strand of mRNA. This reaction requires the action of reverse transcriptase (an RNA dependent DNA polymerase).
cell: The basic unit of life in all organisms which can reproduce itself.
centimorgan: a unit of genetic map distance corresponding to a 1% chance that a marker at one genetic locus will be separated from a marker at a second locus due to crossing over and recombination in one generation.
central nervous system, CNS: the brain and spinal cord that, together, integrate all nervous activities in the body.
CFTR protein: cystic fibrosis transmembrane regulator protein, that is repsonsible for the export of chloride ions across the cell membrane of epithelial cells, including those lining the lungs. Mutations in the gene coding for the CFTR protein may result in impaired function of this protein, leading to symptoms of the autosomal recessive condition of cystic fibrosis.
Charles Darwin: Charles Darwin is most famous for the book 'The Origin of Species' published in 1858, that explained his theory of evolution by the process of natural selection. This theory motivated scientists to reexamine the question of heredity and inheritance that led to the evolution of the field of genetics.
chromosomal abnormality: A condition arising from an organism developing from a zygote having too many or too few chromosomes. Eg. Down Syndrome is caused by a human having three copies of chromosome 21 (trisomy 21)
chromosome: A structure found in the nucleus of a cell, made of DNA and proteins, that contains genes. Chromosomes usually come in pairs.
chronic: describes a condition of long duration and often very slow changes.
cirrhosis (liver): a condition of the liver caused by fibrosis and the formation of regenerative nodules that bring about widespread disruption of normal liver structure and function
cleft lip: a birth defect characterized by a fissure in the upper lip resulting from failure of the embryonic parts of the lip to join
clinical diagnosis: the clinical identification a disease from its signs and symptoms
clone: a cell or group of cells all of which are derived from a single cell by repeated mitoses (cell division) thus all having the same genetic information (DNA).
cloning: production of a group of cells all of which are derived from a single cell by repeated mitoses (cell division) thus all having the same genetic information (DNA).
codon: a sequence of three nucleotides in mRNA that code for a specific amino acid.
complementary: (in molecular genetics) refers to a molecule capable of forming a hydrogen-bonded base pair in DNA or RNA. In DNA, A is complementary to T, and G is complementary to C. In RNA, A is complementary to uracil (U) and G is complementary to C.
complementary base pairing: Pairs of complementary bases interact to form each rung of the DNA double helix, in the formation of mRNA and in the formation and action of tRNA. In DNA, A (adenine) always pairs with T (thymine) and C (cytosine) always pairs with guanine (G). In RNA, there is no thymine, but uracil (U) always pairs with cytosine.
concordance: the percentage proportion of identical twins who both suffer from a disease or exhibit a trait when that disease or trait occurs in one member of the pair. Comparison of concordance between identical and dizygotic twins can be used as a measure of the extent to which genetic factors contribute toward the population variability of a trait.
contiguous: the region of a physical chromosome map defined by a group of overlapping cloned fragments
co-segregating: when alleles at two genetic loci segregate together and, as a single unit, in a way that follows Mendel's laws of inheritance
cosmid: a cloning vector derived from the bacteriophage lambda, that is capable of carrying large segments of DNA (up to 40 kilobases) into cells.
cystic fibrosis (CF): A genetic disease with symptoms that usually appear shortly after birth. They include breathing difficulties and respiratory infections due to accumulation of sticky mucous problems with digestion and excessive loss of salt in sweat.
cytoplasm: the jelly-like part of a cell that surrounds the nucleus.
cytosine, C: One of the nitrogenous bases occurring in DNA and RNA
demyelination: a process that damages the myelin sheaths around nerve fibres. This reduces the function of the nerve fibres in transmitting impulses to or from the central nervous system.
deoxyribose sugar: a pentose (5 carbon)sugar that is a structural element of DNA nucleotides
diabetes: (diabetes mellitus) is a disorder of carbohydrate metabolism that arises when an individual has an inability to process sugars that enter their blood stream.
diagnosis: the identification a disease from its signs and symptoms
dizygotic (DZ) twins: twins derived from the simultaneous fertilisation of two eggs by two sperm. They are not genetically identical, may be two different sexes amd are no more alike than normal brothers and sisters.
DNA, deoxyribonucleic acid: The fundamental substance of which genes and chromosomes are composed. A double chain of linked nucleotides, with each nucleotide consisting of a phosphate, a deoxyribose sugar and one of four bases: adenine (A), guanine (G), cytosine (C) and thymine (T)
dominant: refers to a trait or characteristic that is expressed when an individual is homozygous OR heterozygous for the allele coding for it. Only one copy of the allele needs to be present for it to be expressed.
dopamine: a neurotransmitter acting on specific receptors in the body, especially in the brain and circulatory system.
double helix: Describes the shape of the DNA molecule. It has two strands (double) which are twisted around each other in a spiral (helix).
Down's syndrome: a genetic condition resulting from an extra chromosome 21 (trisomy 21). Characteristics may include a flat facial appearance with slanting eyes, broad hands and short fingers and short stature. Downs syndrome individuals may have a degree of mental handicap, although there is a wide range of ability. Other features may include heart defects and deafness. Approximately 1 birth in 1000 has Down syndrome.
Drosophila melanogaster: a fruit fly species commonly used as a model organism to study genetics and developmental biology.
Duchenne muscular dystrophy: a genetic, sex-linked disorder affecting 1 in 3300 boys. It is characterised by progressive failure of muscle growth and dystrophy (wasting). This leads to weakness, paralysis and respiratory difficulties. Muscles in the heart, smooth muscle, central and peripheral nervous systems may also be affected. Onset of symptoms is usually at about age 3, with patients confined to wheelchairs in their teens
dystrophin: a long rod-like protein molecule that links actin fibres in muscle cells to connective tissues and is required for the function and maintenance of muscle cells. Mutations in the gene coding for dystrophin (the DMD gene) results in Duchenne muscular dystrophy.
eczema: a common skin disease characterised by itching, reddening and vesicle formation.
egalitarian: a person with a belief in human equality especially with respect to social, political, and economic rights and privileges
egg: a mature female sex cell (also called an ovum)
electron microscope: an instrument in which a beam of electrons focused by means of an electron lens is used to produce an enlarged image of a minute object on a fluorescent screen or photographic plate
embryo: an animal at an early stage of development, before birth
embryonic stem cell: embryonic cells with the potential to grow into many different cell types. In theory, human ES cells could one day be used to generate specific tissues for transplantation that have the same set of immunological markers as the patient from whom the cell culture was initiated.
emphysema: a condition in which the alveoli of the lungs become enlarged and damaged. This reduces the surface area for oxygen and carbon dioxide exchange. Symptoms include breathlessness that is worsened by infections. Patients may become dependent on an artificial oxygen supply. The exact cause of emphysema is unknown, but genetic factors, smoking, chronic bronchitis and advancing age all appear to be factors.
endometriosis: A disease caused by tissue similar to that lining the uterus escaping and growing in the pelvis, often on other organs such as the colon or the bladder. Symptoms may include severe pelvic pain, a disturbed menstrual cycle and infertility in severe cases.
environment: the sum of factors (physical, chemical, and biotic) that act upon an organism or an ecological community and ultimately determine its form and survival. For humans in particular this will also include social and cultural conditions that influence the life of an individual or community.
enzyme: a protein that acts as a catalyst, affecting the rate at which a chemical reaction occurs in a cell, without itself being used up in the reaction.
epidermis: the outer layer of the skin.
Eschericha coli: Escherichia coli is a rod-shaped bacterium that is commonly used in laboratory experiments for genetic and microbiological studies. It is a common bacterium found in the gastro-intestinal tract of many animals and is not usually pathogenic.
EST (expressed sequence tag): Expressed Sequence Tag. The site of a tagged sequence derived from a cDNA clone. (cDNA, derived from mRNA in the cell, represents genes, minus introns, that have been expressed in that cell)
etiological: assigning or seeking to assign a cause of a specific disease
eugenicist: a supporter or advocate of eugenics
eugenics: the science that deals with the improvement of hereditary qualities of a race or breed (eg. by selective human breeding)
evolution: a theory that modern animals and plants have their origin in preexisting organisms and that the differences are due to modifications in successive generations. Darwin developed the model of natural selection to explain how this process could occur.
exon: The parts of a gene that are transcribed and remain in mRNA after splicing. This includes translated regions of the gene (protein coding regions) as well as 5' and 3' untranslated regions of the mRNA molecule.
exon trapping: a special technique used to search for exons (protein-encoding sequences) in genomic clones.
factor VIII: a clotting factor protein normally present in the blood. The gene coding for factor VIII is found on the X chromosome in humans. A mutation in this gene in males may lead to the disease Haemophilia A, where a person's blood does not clot normally. (see also X-linked)
familial: tending to occur in more members of a family than expected by chance alone
fertilisation: fusion of an egg and sperm cell. Following penetration of the egg by the sperm, completion of the second meiotic division of the egg occurs, followed by fusion of genetic material from the sperm and egg pronuclei.
fertilise: fertilisation occurs when a sperm fuses with an egg during sexual reproduction. The genetic material from the two gametes combine in the new organism or offspring.
fertility: ability to produce children. This term is often used in a comparative sense, with an increase in fertility referring in an increase in number of children. Fertility rate refers to the nubmer of live births occurring in a year per 1000 women (of child bearing age).
fibroma: a non-malignant tumour of connective tissue.
Founder effect: occurs when a higher than normal frequency of a mutant allele is observed in a once rapidly expanding population founded by a small ancestral group in which one or more of the founders was, by chance, a carrier of the mutant allele.
founding population: the group of individuals from which a population has been derived. A small founding population may lead to less genetic variation in later generations compared to populations that originated from a larger number of individuals.
Frances Crick: Frances Crick was a British biophysicist who worked with an American biochemist called Frances Crick. In 1953 they discovered the double helix structure of DNA and were awarded a Nobel Prize for this work
gamete: A sex cell that contains only half the normal number of chromosomes and fuses with another sex cell during sexual reproduction to from a zygote. Female gametes are called eggs or ova. Male gametes are called sperm or spermatozoa.
gene: a fundamental unit of heredity. A sequence of DNA that codes for a specific product. Most genes code for a protein. A few code for RNA molecules involved in protein synthesis.
gene characterisation: investigation of structure, function and regulation of a gene
gene pool: the total genetic content of all members in a population
gene therapy: treatment of an inherited disease by the addition, insertion or replacement of a normal gene into a patient's cells
genetic code: The sequence of nucleotides, coded in triplets (codons) along mRNA, that determines the sequence of amino acids in a protein. The DNA sequence of a gene determines the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence of the resulting protein.
genetic determinism: the belief that the genetic code determines all facets of an individual
genetic disorder: a condition caused by a genetic mutation. The mutation may be inherited or arise spontaneously.
genetic engineering: the modification of the characteristics of an organism by manipulating its genetic material (DNA.)
genetic map: the relative positions of genes and markers as determined by recombination frequencies/linkage information.
genetic marker: a feature (usually a specific DNA sequence) that identifies a unique location on a chromosome. Polymorphisms are useful genetic markers as they can help distinguish DNA that arises from different origins. A similar polymorpic marker may indicate a common ancestor, and origin of DNA.
genetic testing: analysis of an individual's DNA for a disease-related mutation. The individual can be tested to predict or diagnose disease or carrier status.
genetics: The study of inheritance and how particular traits or features are transmitted from one generation to the next.
genome: the total sum of DNA or genetic material of an organism
genotype: the genetic make-up of an organism
glycoprotein: a compound comprised of a protein molecule combined with a carbohydrate molecule.
growth factor: a polypeptide molecule produced by cells that stimulates them to grow and divide
guanine, G: One of the nitrogenous bases occurring in DNA and RNA
haemochromatosis: an inherited disorder of iron regulation in the body that leads to excessive absorption and storage of iron. This may result in damaged and impaired function of major organs, especially the liver, pancreas and endocrine glands. It is inherited as an autosomal recessive condition.
haemoglobin: a protein found in red blood cells that binds with oxygen, carrying it to all parts of the body.
haemoglobinopathies: a group of genetic conditions in which there is an abnormality in the production of haemoglobin. Conditions include thalassaemia and sickle cell disease.
haemophilia: a genetic disorder in which the blot clots very slowly due to a deficiency in a blood clotting factor (either factor VIII or factor IX).
Heberden's nodes: a lump of cartilage covered bone arising at the end joint of a finger in osteoarthritis.
heredity: the transmission of qualities and traits from ancestor to descendant through genes
hermaphrodite: an individual in which both male and female sex organs are present.
heterogeneous: consisting of several dissimilar forms
heterozygosity: state of being heterozygous (possessing two different alleles of a particular gene, one inherited from each parent
heterozygote: an individual who has two different alleles for a given gene.
heterozygous: possessing two different alleles of a particular gene, one inherited from each parent.
histone, histones: proteins found in eukaryotic nuclei that form complexes with DNA called "nucleosomes".
homeodomain protein: a protein with a DNA-binding motif of 60 amino acids encoded by a homeobox(a short conserved DNA sequence, found in genes that are invovled in control of development in a wide range of organisms).
homologous: (for genes) refers to genes in two different species with similarity in DNA sequence that suggests a common evolutionary origin. (for chromosomes) refers to a pair of chromosomes that contain the same genes at the same loci, one derived from each parent. Eg. the two copies of chromosome 1 in humans are homologous to each other.
homologue: refers to a gene in a species with similarity in DNA sequence to that in another species that suggests a common evolutionary origin.
homology: used to describe the relationship between DNA sequences that have fundamental similarities that indicate a common evolutionary origin. This term is also used to describe organs or structures that have basic similarities and therefore a common evolutionary origin, although superficially they may look or function differently.
homozygous: having two identical alleles at a specific locus
hormonal: describes a process regulated by a hormone (or hormones). Hormones are chemical messengers produced by endocrine glands, secreted into the blood stream and carried to target organs that modify their structure or function in response.
hormone: a chemical substance produced in one part of the body that is transported via the bloodstream to target organs or tissues where it acts to modify their structure or function.(a chemical messenger in the body)
Human Genome Project: a coordinated international effort to characterise all human genetic material by determining the complete sequence of the DNA in the human genome. The ultimate goal of the HGP is to discover all human genes and make them accessible for further biological study.
human leucocyte antigen (HLA): human leucocyte antigens. These are coded for by a series of four gene families and are expressed on the surfaces of most nucleated cells. Two individuals sharing the same HLA types are said to be 'histocompatible'. Transplantation of tissue depends on a minimum number of differences existing between the donor and recipient tissues.
hydrogen bond: an electrostatic attraction between a hydrogen atom in one polar molecule and a small electronegative atom (as of oxygen, nitrogen, or fluorine) in another molecule. In DNA hydrogen bonds link the nitrogen of bases in one chain to the complementary bases in the other chain. These bonds are relatively weak and easily broken and reformed.
hydrophilic: describes a molecule, or part of a molecule, that forms enough hydrogen bonds to water to allow it to dissolve readily in water.
hydrophobic: describes a molecule, or part of a molecule, that does not dissolve in water.
hyperactivity: a condition of being excessively active
immune system: the organs and cells that protect the body from foreign substances, cells, and tissues.
in situ hybridisation: hybridisation of a labelled nucleic acid probe to chromosomes spread on a slide that can then be visualised. This can be used to physically map a gene to a chromosome.
in vitro: describes a biological process made to occur outside the living body and in an artificial environment (eg such as a test tube)
in vitro fertilisation (IVF): fertilisation of an egg cell outside the body. The resulting zygote is incubated until it reaches the blastocyst stage and them implanted into the uterus and the pregnancy is allowed to continue as normal.
in vivo: describes a biological process that occurs within the body of a living organism
inbreeding: the production of offspring by parents who are closely related. there is a high likelihood that two closely related individuals will carry similar deleterious recessive mutations that may be expressed phenotypically in the offspring, thus inbred populations my have a higher than average incidence of recessive genetic disorders.
independent assortment: During gamete formation the segregation of alleles of one gene is independent to the segregation of alleles of another gene (Mendel's 2nd Law). This means that members of different gene pairs segregate to offspring independently of one another. (This is true except in the case of linked genes, ie. those found close together on the same chromosome that do not assort independently.)
infertility: inabilty to have children
inflammatory: causing a response to injury (that may be caused by infection, chemicals or physical agents). This response (inflammation) involves pain, redness, swelling and dilation of blood vessels in that area.
inherit: to receive from an ancestor. In terms of genetics, offspring inherit genes from their parents.
inherited: Received from an ancestor. In terms of genetics, offspring inherit genes from their parents.
insertion: describes a mutation involving the addition of one or more nucleptides into a gene.
insulin: hormone produced by the beta cells of the Islets of Langerhans in the pancreas to regulate blood sugar levels. Secretion of insulin is stimulated by a high concentration of sugar in the blood. Insulin acts to bring about a reduction of blood sugar levels to normal.
insulin dependent diabetes melitus (IDDM): a disorder of carbohydrate metabolism that arises when an individual has an inability to process sugars that enter their blood stream. IDDM is caused by a relative or complete lack of insulin secretion by the beta cells of the pancreas. This can result in very variable blood sugar levels that may be very high or low. Symptoms include low energy levels, extreme thirst, weight loss and an excessive production of urine.
intra-cytoplasmic sperm injection (ICSI): This is a form of IVF (in vitro fertilisation) that involves direct injection of a single sperm into the cytoplasm of an ovum. The resulting zygote is then implanted into the uterus at the blastocyst stage.
intron: the portion of DNA in a gene that is transcribed into mRNA but removed by splicing before transcription. It does not code for protein structure.
inversion: a chromosomal section that has undergone a breaking off and subsequent reattachment in an inverted (back to front) position.
James Watson: James Watson was an American biochemist who worked with a British biophysicist called Frances Crick. In 1953 they discovered the double helix structure of DNA and were awarded a Nobel Prize for this work.
karyotype: representation of the set of chromosomes in a somatic cell, described by number, size, shape and banding patterns. This can be used to detect chromosomal abnormalities (eg. Down syndrome) in an individual.
karyotyping: representing the set of chromosomes in a somatic cell, described by number, size, shape and banding patterns. This can be used to detect chromosomal abnormalities (eg. Down syndrome) in an individual.
keratin: one of a family of proteins that are the major components of hair, nails and the outer layer of the skin
kilobase: one thousand base pairs
Klinefelter's syndrome: a genetic disorder where an individual has three sex chromosomes; two X chromosomes and one Y chromosome (XXY). Affected individuals are male and infertile.
knockout (mouse): experimental mice created by deleting or disrupting the function of a specific gene
laparoscopy: a surgical procedure involving examination of abdominal structures by means of an illuminated tubular instrument (a laparoscope) that is passed through a small incision in the abdominal wall. It can be used for diagnosis and treatment of some conditions.
leucocyte: a white blood cell. Leucocytes include granulocytes, monocytes and lymphocytes. They are the principal cells involved in protecting the body against infection.
ligand: a molecule that binds to a specific site on a protein or other molecule.
linkage: The tendency of two genetic loci to be inherited together through meiosis more frequently than genes that assort independently. This implies that the two genes are on the same chromosome and are located close together.
linkage disequlibrium: the tendency of specific alleles at one locus to be associated with specific aleles at another, closely linked locus. This may occur when most cases of a disease in a population are caused by a single mutation in a common ancestor. Alleles that are closely linked to the mutation site will be commonly inherited by all individuals who have inherited the mutation.
linkage map: A map of the relative positions of genetic loci on a chromosome, determined on the basis of how often the different genes are inherited together. Genes that are located close to each other will tend to be inherited together and are described as linked.
loci: plural of locus: a unique position on a chromosome occupied by a gene or some other DNA sequence
locus: a unique position on a chromosome occupied by a gene or some other DNA sequence
low-resolution mapping: assigning a gene or DNA fragment to a chromosome or region of a chromosome.
major histocompatability complex (MHC): a series of genes, found on human chromosome 6, that code for antigens that are found on the surfaces of cells. These proteins are used by the immune system to distinguish between cells that are 'self' and those that are 'non-self- or foreign.
malignant: (cancer)refers to a tumour with tending to infiltrate tissues, metastasise, and potentially cause death
marker locus: a DNA sequence that identifies a unique location (locus) on a chromosome
medulloblastoma: a cerebral tumour that arises in childhood.
meiosis: a form of cellular division resulting in the production of four daughter cells, each with half the number of chromosomes of the parent cell. The products of meiosis may form into gametes (sperm and ova). Chromosome number of the species is restored after fertilisation.
melanocyte: cells in the epidermis of the skin that produce the pigment melanin
melanoma: a highly malignant form of skin cancer. Melanomas arise from melanocytes that have become cancerous in their growth. They are often fast growing, and if not treated may metastasise and spread into the dermis layer of the skin and the blood stream.
Mendel: Gregor Mendel was an Austrian monk in the 1850s who used the results of his breeding experiments on peas to explain the particulate nature of inheritance (genes). In essence, his work is now considered to be the discovery of genes and how they are inherited. His laws of segregation and independent assortment are used to predict the inheritance of single gene characteristics.
Mendel's 1st law: The law of segregation. Each individual possesses two genes for a particular characteristic. Only one of each gene pair will be passed on to each gamete. The two members of a gene pair segregate from each other into the gametes, so that one half of the gametes carry one member of the pair and the other half of the gametes carry the other member of the pair.
Mendel's 2nd law: The Law of Independent Assortment. During gamete formation the segregation of alleles of one gene is independent of the segregation of alleles of another gene.
menstrual cycle: the hormonally controlled cyclic sequence of events occurring in sexually mature women. An egg cell is released from the ovary every 28 days. If it remains unfertilised menstruation (shedding of the endometrium) will occur prior to another egg cell being released. The cycle does not continue if fertilisation occurs, but implantation and foetal development will occur.
metabolic pathway: a series of linked reactions occurring within a living cell to produce a specific product, or products. The product of one reaction becoming the input of the next. Each step in the pathway is usually controlled by a specific enzyme.
metabolise: to process biochemically within a cell
metabolite: a substance that is a product of a cell's metabolism or a substance that is essential to the metabolism of a particular metabolic process.
metastasise: describes the process of a tumour spreading by metastasis (most commonly when tumour cells break away, enter the blood stream and travel to other parts of the body to form secondary tumours)
methionine: a sulphur-containing essential amino acid. The mRNA codon coding for methionine also serves as a start codon which is involved in initiating translation of an mRNA molecule into a polypeptide chain.
microsatellite: short tandem repeats (STRs) of DNA units, 2 to 4 base pairs in length, found at many different loci in the genome, including both coding and non-coding regions.
mimic: a copy or imitation
mitochondria: organelles within a eukaryotic cell that are the site of aerobic respiration. They provide most of the energy that can be used by the cell.
mitosis: The process of nuclear division in cells that produces daughter cells that are genetically identical to each other and to the parent cell. Mitosis leads to production of new body cells needed for growth and repair and is also used by organisms who asexually reproduce.
molecular biology: the study of molecues that are associated with living organisms, including DNA and proteins
molecular genetics: the study of genetics/inheritance at the cellular/molecular level, including DNA structure and function and protein synthesis
molecule: A molecule is a group of atoms arranged to interact in a particular way and forms the smallest physical unit of that substance that retains all of the properties of that substance.
monogenic: a trait or feature determined by a single gene pair
monozygotic twins: identical twins, that have developed from a single fertilised egg that has divided to form two separate foetuses.
morbidity: a state of being diseased. The term morbidity may also be used to describe the relative incidence of disease.
motor neuron: nerve cell that carries nervous impulses from the central nervous system to an effector organ, such as a muscle or gland.
mRNA: messenger RNA. RNA that is transcribed from DNA in a gene. It carries genetic information from the nucleus to the ribosomes where it directs the synthesis of the protein coded for by that gene.
multi-factorial: produced or controlled by a number of factors, that may be genetic and/or environmental
multiple sclerosis: a chronic disease of the nervous system caused by demyelination of nerves in the brain and spinal cord.
murine: relating to or involving the mouse
muscular atrophy: the wasting away of normally developed muscle tissue.
mutagenesis: the occurrence or induction of a mutation. In laboratory conditions mutation rates can be increased by the application of mutagens that include UV light and some chemical agents.
mutate: change the genetic material of a cell. This can occur at the level of a single gene or involve a whole chromosome.
mutation: a change in the number, arrangement, or molecular sequence of a gene. Only mutations that occur in germ cells (resulting in eggs or sperm) will be passed on to new generations.
mutation analysis: identification of mutations within a gene that lead to changes in phenotype, usually in the context of genetic disorders
mutligenerational: spanning many generations
myosin: the most abundant protein found in muscle fibres. It works with actin to bring about muscle contraction.
myotonic dystrophy: a genetic neuromuscular disorder, inherited in an autosomal dominant pattern, characterised by myotonia (delayed muscle relaxation) and degeneration of organs such as the heart and eyes in very severe cases. Milder symptoms include frontal baldness and cataracts. it is the most common form of muscular dystrophy seen in adults and has an incidence of about 1 in 8000.
nanometre: one billionth of a metre ( 1 metre = 10 to the power of 9 nanometres)
natural selection: the model used by Charles Darwin to explain his theory of evolution. He described it as a natural process that results in the survival and reproductive success of individuals best suited to their environment. This leads to the development of genetic qualities in a species that best suit it to that particular environment.
neurological: pertaining to the study of the nervous system, especially in respect to its structure, functions, and abnormalities
NHMRC: National Health and Medical Research Council
non-insulin dependent diabetes melitus (NIDDM): a disorder of carbohydrate metabolism that arises when an individual has an inability to process sugars that enter their blood stream. NIDDM is caused by a lack of responsiveness to insulin. This can result in very variable blood sugar levels that may be very high or low. Symptoms include low energy levels, extreme thirst, weight loss and an excessive production of urine.
northern blot: the transfer by absorption of mRNA fragments separated by gel electrophoresis, onto a membrance filter for detection of specific sequences using labelled, complementary probes. This process allows the size and expression of mRNA molecules to be investigated.
nucleic acid: a complex organic acid molecule composed of nucleotide subunits. The two main nucleic acids DNA and RNA are found in the nucleus, and sometimes the cytoplasm of cells. Their main functions are in heredity and protein synthesis.
nucleosome, nucleosomes: a basic unit of DNA packaging in which about 140 base pairs of DNA wind around 8 histone protein molecules. About 60 base pairs stretch to the next nucleosome, forming a packaging pattern that resembles a string of beads.
nucleotide: the 'building block' of nucleic acids (DNA, RNA). A molecule that consists of a ribose or deoxyribose sugar joined to a nitrogenous base and to a phosphate group.
nucleus: The part of a eukaryotic cell where genetic material (chromosomes) are found. It is separated from the cytoplasm of the cell by a double membrane called the nuclear envelope.
obesity: a condition in whic excessive fat has accumulated in the body. A person is usually considered obese when they are 20% above the recommended weight for their height and build.
organelle: a structure within a cell that is specialised for a particular function. Eg. ribosomes are organelles specialised for synthesis of proteins.
osteoarthritis: a form of arthritis associated with degeneration of the cartilage in joints, and associated with secondary changes in the underlying bones. This can cause pain and may impair function of the joint, most commonly in the hips, knees and thumbs.
osteophytes: projections of bone that occurs at sites of cartilage degeneration near joints.
outbred: refers to offspring produced by parents who are not closely related.
ovulate: release an egg cell from the ovary
PAC: P1-derived Artificial Chromosome.
pathogenesis: the origin and development of a disease
PCR (polymerase chain reaction): a technique used to amplify (make many copies of) a given segment of DNA.
pedigree: a diagram, similar to a family tree, that charts the incidence of a particular trait through many generations of a family.
pelvic: pertaining to the pelvis (the lower part of the abdomen)
phenotype: the properties of an organism that are produced by the interaction of the genotype and the environment
phenylketonuria: an inherited autosomal recessive disorder that results from a lack of the enzyme phenylalanine hydroxylase. This leads to accumulation of the amino acid phenylalanine that can impair development of the nervous system and cause mental subnormality. If detected early patients are placed on a low phenylalanine diet that allows normal nervous system development.
phospho-diester bond: strong covalent bonds linking nucleotides together in a polynucleotide chain.
physical map: a map of the actual location of genes and markers along a chromosome as determined by techniques such as FISH, restriction mapping and physical cloning. In comparison, a genetic map shows relative positions of genes on a chromosome calculated from recombination frequencies.
point mutation: a mutation involving change of a single base pair.
polygenic: refers to a trait controlled by the combined action of a number of genes (e.g., heart disease, skin colour). Such conditions tend to have a more complex inheritance pattern than single gene conditions. The expression of these genes may also be dependent on the environment of the individual.
polyglutamine expansion: a greater than usual number of glutamine amino acid units in a protein product translated from an expanded number of tandem (CAG) trinucleotide repeats within the coding sequence of a gene.
polymorphic: refers to naturally occurring variations in the DNA sequence of a particular gene.
polymorphism: the occurrence in a population of several phenotypic forms independent of variations associated with sex. These different forms are usually associated with alleles of a gene.
polynucleotide: a large molecule comprised of many nucleotides linked together.
polypeptide: a molecule consisting of three or more amino acids linked together by peptide bonds.
positional cloning: cloning of a gene using information from its chromosomal location
predispose: To have a tendency or inclination towards something in advance.
predisposition: a tendency to be affected by a particular condition. This tendency may be inherited or due to environmental factors. To have a genetic predisposition for a particular condition is to have a greater probability than most for developing that condition due to the possession of particular alleles of a gene (or genes).
pre-implantation genetic diagnosis (PGD): diagnosis of genetic status of an embryo prior to implantation. This procedure requires the removal and in vitro fertilisation of egg cell. Three days after fertilisation one or two cells are removed from the embryo. Alternatively, tissue may be removed from an embryo at five or six days when it is at the blastocyst stage. The isolated cells can then be analysed for specific chromosomal conditions and other genetic disorders.
prognosis: an assessment of the course and outcome of a patient's disease as anticipated from knowledge of the course of the disease in other patitents and with the general health of the patient.
protein: Any of a group of organic compounds formed from amino acids, which are found in all cells and include enzymes, plasma proteins and structural proteins.
psoriasis: a chronic skin disease characterised by itchy, scaly, pink patches forming on the scalp, elbows, knees and other parts of the body. In a few cases the disease may be very severe, affecting most of the skin and causing considerable disability for the patient.
purine: A nitrogen-containing basic compound with a double ring molecular structure that occurs in nucleotides. The purines in DNA and RNA are adenine and guanine.
putative: refers to a gene or protein that is assumed to be the one sought, but not proven
pyrimidine: A nitrogen-containing basic compound with a single ring molecular structure that occurs in nucleotides. The pyrimidines in DNA are cytosine and thymine and in RNA are cytosine and uracil.
receptor: a protein molecule on the cell surface or in the cell interior that has an affinity for a specific chemical group, molecule, or virus.
recessive: refers to a trait that is expressed only if an individual is homozygous for the allele coding for it (ie. has two copies of that allele.) This trait is masked in a heterozygote by the presence of a dominant allele.
backrenal: relating to or affecting the kidneys
restriction map: a map of a DNA sequence, usually in base pairs, indicating the location of sites digested by specific restriction enzymes
reverse transcription: synthesis of double-stranded DNA from an RNA template. The enzyme reverse transcriptase is required to catalyse this reaction. Reverse transcription occurs naturally with some RNA viruses (eg. the HIV virus), but has also proved a useful tool for molecular geneticists.
RFLP: (restriction fragment length polymorphism) a genetic marker based on the presence or absence of a target for a restriction enzyme due to a polymorphism at a single base pair. This polymorphism will give variation between individuals in DNA fragment sizes cut by specific restriction enzymes that can be used as markers on physical and genetic linkage maps.
rhabdomyosarcoma: a malignant tumour starting in striated muscle.
rheumatoid arthritis: a form of arthritis involving inflammation of the joints of the fingers, wrists, feet, ankles and sometimes the hips. There is a wide range of severity of the disease.
ribose sugar: a pentose (5 carbon) sugar that is a structural element of RNA nucleotides
RNA polymerase: an enzyme that synthesises the transcription of mRNA from a DNA template
RNA, ribonucleic acid: Ribonucleic acid (RNA): A nucleic acid found in the nucleus and cytoplasm of cells that plays an important role in protein synthesis. RNA is typically single-stranded and is comprised of a polynucleotide chain. Each nucleotide is made up of a phosphate, a ribose sugar and one of four nitrogenous bases: adenine, guanine, cytosine or uracil.
rRNA: ribosomal RNA. A class of RNA molecules that forms structural elements of ribosomes.
sex cell: A sex cell (gamete)contains only half the normal number of chromosomes and fuses with another sex cell during sexual reproduction to from a zygote. Female sex cells are called eggs or ova. Male sex cells are called sperm or spermatazoa.
sex chromosome: Chromosomes that determine the sex of an individual. In humans females have two X chromosomes and males have one X and one Y chromosome.
sex-linked: describes a trait showing a pattern of segregation characteristic of a gene located on one of the sex chromosomes (X or Y). In humans most sex-linked traits are X-linked as the X chromosome contains many more genes than the smaller Y chromosome.
sib pair analysis: genetic analysis based on two siblings affected by a disease. (see affected sib pair analysis)
sibling: one of two or more individuals having at least one common parent (brothers and sisters)
sickle cell anaemia: a condition caused by a mutation in the beta globin gene leading to production of abnormal haemoglobin. This causes the red blood cells to take on a distorted 'sickle' shape which severely reduces oxygen carrying capacity. Sickle cell anaemia is inherited as an autosomal recessive trait.
southern blot: the transfer by absorption of DNA fragments separated by gel electrophoresis, onto membrane filters for detection of specific DNA base sequences using radioactively labelled complementary nucleic acid probes
sperm: A mature male sex cell
splice donor site: junction site between the end of an exon and the start of a downstream intron (the intron will be spliced out, beginning at this site). It normally starts with the dinucleotide sequence GT.
spontaneous DZ twins: spontaneous DZ twins result when multiple ovulation occurs spontaneously, naturally, or without intervention rather than being induced by pharmacological stimulation
sporadic: describes a disease or condition that occurs only ocaasionally an does nto appear to be familial.
SSCP (Single-Strand Conformation Polymorphism) A technique used to detect base changes without sequencing or defining the nucleotide affected.
stop codon: a nucleotide triplet in mRNA that signals the end of protein synthesis. Three mRNA codons code for stop: UAA, UAG and UGA.
stroke: a sudden attack of weakness affecting one side of the body. It is usually caused by a disruption of blood flow to a region of the brain. A stroke can range in severity from a passing weakness and tingling in a limb to paralysis, coma or death.
sugar: a simple carbohydrate molecule, composed of hydrogen, carbon and oxygen with the general formula Cx(H2O)y. Sugars are usually crystalline, soluble in water and have a sweet taste. The sugar in DNA nucleotides is deoxyribose. The sugar found in RNA nucleotides is ribose.
synaptic: of or relating to a synapse (the minute gap between adjacent neurons across which nerve impulses pass. As an impulse reaches a synapse, a neurotransmitter is released that diffuses across this gap and stimulates an electrical impulse in the next neuron.)
synovial (joint): a freely moveable joint, such as the wrist or ankle.
systemic: affecting the body as a whole, not just individual organs or tissues.
T-lymphocyte: (also known as T cell) a type of white blood cell that differentiates in the thymus. They have highly specific cell-surface antigen receptors and are primarily involved with cell mediated immunity.
Tay Sach's disease: an inherited, autosomal recessive disorder that results in a progressive neurological degeneration. This is caused by a mutation in the HEXA gene that leads to a build up of the lipid ganglioside that impairs neurone function. This leads to developmental and mental retardation, progressive muscle weakness, paralysis and blindness and most patients die by the age of 5 years.
thalassaemia: a group of inherited blood disorders resulting from an imbalance of globin proteins in the haemoglobin molecule in red blood cells. This leads to mild or severe anaemia. Other symptoms may include an enlarged spleen and anormalities in the bone marrow. Severe cases of the disease occur in patients who are homozygous for a mutation in one of the globin genes. Heterozygotes may be only mildly affected or have no symptoms at all. Thalassaemias are widespread in Mediterranean countries, Asia and Africa.
therapeutic: refers to a method of treatment of a disease or disorder, providing or assisting in a cure
therapeutics: the branch of medical science that deals with different methods of treatment and healing disease
thymine, T: One of the nitrogenous bases occurring in DNA and RNA
trait: an inherited characteristic
transcription: The process of copying information from DNA into new strands of complementary messenger RNA (mRNA). The mRNA then carries this information to the ribosomes where it directs synthesis of a specific protein. The enzyme RNA polymerase is needed for transcription.
transformation: 1. process in which foreign DNA from one bacterium is introduced into a recipient bacterium and incorporated into its chromosome. 2. acquisition of cancerlike properties by cultured animal cells following treatment with a virus or carcinogen
transgenic: describes an organism or cells that have a foreign gene introduced into their genome
translation: the process by which transcribed mRNA directs the synthesis of a specific protein. Translation takes place in the cytoplasm, on structures called ribosomes.
transmembrane protein: a protein located across a membrane
transmission disequilibrium test: is used to check the results of an association study. They can confirm whether a parent heterozygous for a disease -associated and non disease-associated allele transmits the associated allele more often to affeted offspring.
triad: (for genetic studies) an affected individual plus both of their parents
tRNA: transfer RNA. A class of small RNA molecules that transfer a particular amino acid to a growing polypeptide chain during protein synthesis at a ribosome. tRNA molecules have a triplet nucleotide sequence (an anticodon) that is complementary to the triplet nucleotide coding sequences of mRNA. The anticodon determines the amino acid transferred by that molecule.
truncation: describes a protein that is shorter than normal, usually due to a mutation that leads to a premature stop codon occurring in the gene coding for that protein.
Turner's syndrome: a genetic condition that arises in women who have only one X chromosome instead of two, resulting in only 45 chromosomes (XO). Affected women are infertile. They are usually short in stature and have variable developmental defects.
twin studies: are used to examine the relative contributions of genetics and environment to a specific trait.
uterus: the part of the female reproductive tract where implantation of an embryo occurs. The young are then nourished during development (via the placenta) in the uterus prior to birth. The uterus consists of an inner mucous lining (the endometrium) and a thick wall made of smooth muscle (myometrium).
X chromosome: One of the chromosomes involved in sex determination in humans. Normal females have two X chromosomes in each somatic cell. Males have only one X chromosome in each somatic cell. They also have a Y chromosome.
X-linked: describes a trait showing a pattern of segregation characteristic of a gene located on the X chromosome.
xyzzy: general xyzzy explanation
Y chromosome: One of the chromosomes involved in sex determination in humans. Normal males have one Y chromosome in each somatic cell and one X chromosome. Females do not have a Y chromosome.
YAC: Yeast Artificial Chromosome
zygote: a fertilised egg, formed from the union of an egg and a sperm.