[Adapted from Genome British Columbia-http://www.genomebc.ca/media/media-resources/glossary]
Genomics uses a lot of jargon that can be hard to understand for those not trained in the field. Our simple glossary has definitions for important or frequently encountered concepts in genomics.
A
Allele
One of two or more forms of a particular gene at a specific position on a chromosome. For example, blue and brown eyes in human beings are determined by different alleles of the eye colour gene.
Allelic heterogeneity
Different mutations in the same gene can leading to the same disease. For example, Duchenne Muscular Dystrophy is caused by large deletions in the dystrophin gene 70% of the time but other mutations in this dystrophin gene can lead to the same disease presentation.
Alternative splicing
The process where the initial strand of RNA copied directly from DNA is cut up (spliced) into different messages (mRNAs) and can lead to different proteins from the same piece of DNA. Thus, one gene can be the source of several proteins that differ in function or time and place of action.
Amino acid view
The building blocks for proteins. Composed of carbon, hydrogen and nitrogen, these organic molecules all contain a basic amino group (NH2) and an acidic carboxyl group (COOH) and hence, the truly logical moniker, amino acid. To keep on living and loving, we humans need 20 of them. Our bodies make 12 and we get the other 8 (the 8 essential amino acids) from our food.
Amniocentesis
A prenatal procedure that can examine the DNA of a fetus. It involves removing a small amount of fluid from around the developing baby (amniotic fluid) with a needle into the uterus. The amniotic fluid has some of the baby’s cells that can undergo various lab tests. It can diagnose genetic disorders based on chromosomes such as Down syndrome or conditions with smaller gene mutations like cystic fibrosis.
Amniotic fluid
The fluid surrounding the fetus in the uterus. It is mostly water but also has cells sloughed off from the fetus, secretions from the placenta and fetal urine. These fetal cells can be examined for chromosomal and genetic disorders.
Apoptosis
The body’s method for disposing of unwanted cells. Otherwise known as programmed cell death, apoptosis is a deliberate ‘suicide’ where a cell dies in an organized way. This is in contrast to necrosis, the ‘messy and violent’ form of cell death. Apoptosis is important when there are a lot of changes such as during fetal development.
Autoimmune disease
Disease in which the immune system confuses the patient’s own cells for foreign cells and attacks them.
Autosome
The chromosomes other than the sex chromosomes. We human beings have 22 pairs of autosomes (chromosomes 1-22) and two sex chromosomes, two Xs if you’re lucky enough to be female and XY if you’re equally lucky enough to be male.
B
Backcross
This is a process used in research to create a plant/animal that is genetically very similar to one of the parents. Offspring are mated with one of its parents or a plant/animal that is genetically similar to the parents to create plants/animals with similar genetic backgrounds.
Base pair
A base is the variable component of a nucleic acid. DNA contains the four bases thymine (T), cytosine (C), adenine (A) and guanine (G). Attached like snap fasteners, these bases form base pairs along the length of the DNA helix. A pairs with T, while G pairs with C. The order of these bases (ATCG) comprise the DNA sequence.
Bioinformatics
Bioinformatics is the science of managing and analyzing biological information, usually with advanced computing techniques.
BLAST
BLAST stands for Basic Local Alignment Search Tool and is a computer program that compares DNA or protein sequences. When you enter your favorite sequence, BLAST searches public biological sequence data for similar sequences. This allows researchers to identify similar genes in the same or other organisms.
BRCA1/BRCA2
BReast CAncer 1 and 2 genes are examples of tumour suppressors that normally help to restrain cell growth. When these genes are mutated and inactivated, cells can grow too much and cancer develops. Someone who has inherited a mutation in BRCA1/BRCA2 has an increased risk of breast (for both women and men), ovarian or prostate cancer.
C
Candidate gene
A gene located in the chromosome region suspected to cause or contribute to a disease. The gene’s function and place of action should suggest a role in the disease in question. For example, the gene coding for a protein that works in the brain and regulates brain transmitters is a good candidate for depression.
Carrier (of a genetic disease)
Someone who has a disease-causing mutation in their DNA but does not show any symptoms. One way this happens is in recessive disorders when someone has one healthy and one faulty version of the disease-causing gene.
Cell view
The smallest unit of life that can exist independently. All organisms are made up of one or more cells.
Chorionic Villus Sampling (CVS)
An idea that information is always transferred from DNA to RNA to protein and cannot go backwards from protein to RNA to DNA or in any other order. However, we now know that information can also be transferred from RNA to DNA (see reverse transcription), from RNA to RNA (by some viruses) and from protein to protein (see prions), although the “central dogma rule” holds true in most instances.
Centromere
A specialized condensed region of each chromosome that holds sister chromatids together until they are separated during cell division (mitosis).
Chorionic Villus Sampling (CVS)
A prenatal procedure that cultures tissue that can be used to examine the DNA of fetal cells from the placenta (chorionic villi). CVS is commonly used to diagnose chromosome conditions like Down syndrome.
Chromosome
A long, twisted and folded-up piece of DNA. Each species has a characteristic number of chromosomes. Humans, for example, have 46, 23 donated from each parent.
Clone
An organism that has the exact same DNA as another organism. For example, plant cuttings are clones.
Codominant
Two different versions of a gene contribute to the final trait so that neither version is masked by the other. For example, if a woman with blood type A passed on the A allele and a man (blood type B) passed on a B allele, their child would be AB.
Codon
Three adjacent bases (letters) in mRNA that “code” for a particular amino acid in protein translation. There are 64 possible 3-letter combinations of the bases but only 20 amino acids, so several of the codons code for the same amino acid.
Complementary
A property of nucleic acids, whereby adenine (A) always pairs with thymine (T) while cytosine (C) always pairs with guanine (G). Two strands of DNA that pair perfectly are called complementary.
Congenital
Referring to a trait in an organism that is present at its birth. The congenital trait can be due to genetic factors, environmental ones or a mixture of both.
Conserved genes
Genes similar across species; that is, conserved through evolution. So they are likely well-used and necessary for survival. For example, all organisms have very similar genes handling DNA through cell division.
Crossing over
A process that occurs during meiosis. Two members of a chromosome pair twist around one another and exchange genetic information. Genetic material is ‘shuffled’ so that each gamete contains a unique combination of its parent’s genes. It’s how, for example, our grandparent traits are shuffled; we have our maternal grandma’s eyes but grandpa’s hair colour.
D
Diploid
The characteristic of an organism or cell having two complete sets of chromosomes in each cell. For example, humans have one set of chromosomes from dad and the other from mom, hence also have two alleles of each gene. Compare to: haploid.
DNA
DNA stands for deoxyribonucleic acid. It is the molecule that contains the genetic instructions to construct and maintain a living organism.
DNA fingerprint
A technique used for identification, for example in paternity tests or crime scene investigations. Relatively large amounts of DNA are isolated and cut by restriction enzymes. The lengths of the resulting DNA fragments are characteristic of each individual (see SNP). Note: this technique has been essentially replaced by DNA profiling.
DNA profiling
A technique used to identify a person based on their DNA. Fragments of the DNA are amplified using PCR and the lengths of the resulting DNA pieces are characteristic of each individual. Because of the PCR step, only very little amounts of DNA are needed for DNA profiling. Compare to: DNA fingerprint.
DNA polymerase
An enzyme that can make new DNA strands from an old strand/template. There are several DNA polymerases in our cells; and although they have slightly different functions, they all are involved in DNA replication.
Dominant
Refers to the allele that is expressed when two different alleles are found together. For example, in the brown and blue alleles for eye color, brown is typically the dominant one. So when someone has one brown and blue allele, he generally has brown eyes. Compare to: recessive.
Down Syndrome
Also called trisomy 21. A chromosome defect that is characterized by the presence of an extra copy of chromosome 21 in a patient’s cells. Down syndrome usually causes delayed mental and physical development and is associated with chracteristic facial features.
Drug target
A key biological molecule that is specific to a disease. A successful drug will block or inhibit this molecule from promoting the disease process.
E
Enzyme
A biological catalyst: a protein that can speed up chemical reactions without getting chemically changed itself. Human saliva contains an enzyme called amylase that speeds up the chemical reaction of converting starches in our food to sugars.
Epistasis
The phenomenon that genes can interact with each other. A gene is epistatic when it changes the effect another gene conveys on the organism.
Eukaryote
An organism that consists of a cell or cells that have membrane-bound organelles. One of these organelles is the nucleus in which DNA is stored. Compare to prokaryote.
Exon
The region of RNA that is translated into protein. In eukaryotes, the primary RNA usually contains several exons that are separated by introns. Before the RNA is translated, the introns are removed and only exons remain. Compare to: intron.
Expressivity (Variable expressivity)
The process of the same mutation leading to different disease manifestations. For example, the same mutations in a breast cancer gene (BRCA1) can lead to breast or ovarian cancer.
G
Gel electrophoresis
A technique to separate biological molecules such as DNA or protein based on their size. An electrical gradient is appled to a semi-solid matrix (the gel) and molecules begin to migrate based on their electrical charge. Because of their smaller size, short pieces of DNA or protein travel through the gel faster.
Gene
The fundamental unit of inheritance. Genes encode messages for the creation of proteins and functional RNAs. Genes help determine an organism’s appearance, its metabolism and sometimes even its behaviour.
Gene expression
The “switching on” and transcription of a gene into RNA. Sometimes this RNA can be functional on its own but usually it’s converted into a protein. Either way, the gene’s information is out there to impact the individual’s phenotype.
Gene family
A set of genes similar in DNA sequence. Their similarity is presumably due to their evolution from a single ancestral gene that duplicated. Although these gene products gained or lost functions over time and became slightly different from their common ancestor, remnants of the ancestral gene are still present in all family members.
Gene knockout
The intentional removal or disruption of function of a gene from an organism’s DNA. For example, a p53 knockout mouse is a mouse that lacks the gene encoding for the p53 protein. Knockout mice are often used to study the function of the knocked-out gene by noting what changes are observed in the mutated mouse.
Gene therapy
The process of replacing ‘faulty’ genes involved in inherited diseases with ‘corrected’ versions. For most genetic disorders, gene therapy is still in the very early stages of development. However, it has been successfully applied to cure severe combined immunodeficiency (SCID) in limited, controlled clinical settings.
Genetic counselor
Health professionals that provide information and support to families at risk for or affected by a genetic condition. Genetic counselors translate complex genetic information into everyday language to help people make informed decisions about the issue at hand. They strive to discuss information and present options in a non-biased way to encourage patients to make decisions fitting with their own personal values and beliefs.
Genetic engineering
The direct manipulation of an organism’s DNA; in contrast to traditional breeding, where the DNA is manipulated indirectly. Many different techniques are used in genetic engineering, including the examples of gene knockouts and transgenic organisms.
Genetic testing
Using tests to diagnose or determine the predisposition to a genetic disease. The type of test can vary and includes tests directly on DNA, as well as biochemical tests that analyze proteins or metabolites linked to genetic diseases. The tests can also be used to prove paternity.
Genetically Modified Organism (GMO)
Organisms that have had their DNA altered by genetic engineering. When scientists generate GMOs, they combine existing pieces of DNA in new ways to give an organism new characteristics.
Genome
The entire genetic information content of an organism. For most organisms the genome is made up of DNA, but for some viruses it is RNA. When we hear that a ‘genome has been sequenced’, it means that the sequence of all the base pairs (A, T, C, and G) that make up the DNA of that organism have been determined.
Genomics
The science that aims to decipher and understand the entire genetic information of an organism. As such, this science is fundamental to all biological research. It is typically large scale, broad scope and has a reliance on data collection, analysis and information technology (bioinformatics). Conversely, classic biology research is typically focused on a single protein, and the affects its properties have on the organism.
Genotype
The specific set of alleles contained in the DNA of an organism. The genotype, as well as environmental and epigenetic factors, determine the final traits. Compare: phenotype
Germline
The group or line of cells that gives rise to reproductive cells (sperm or eggs). Mutations in the germ line are passed on to future generations. Cells that are not part of the germline are called somatic cells.
H
Haploid
The characteristic of an organism or cell having only one set of chromosomes and therefore only one allele of each gene. Human sperm and egg cells, for example, are haploid. When they combine during fertilization, they form a diploid (containing two sets of chromosomes) embryo. Compare to: diploid.
Heritability
Is an expression of how much of the variation in a trait in a population is due to genes as compared to how much is due to environment. If a trait has a high heritability it generally means that genetic factors strongly influence the amount of variation.
Heterozygous
An individual having two different alleles of the same gene. When a person inherited a ‘brown gene’ and a ‘blue gene’ for eye color, (s)he is heterozygous for the eye color gene. Compare to: homozygous.
Homologous
From “Homology”: the characteristic of genes or organisms being similar due to a shared ancestry. Homology can be subdivided into orthology and parology.
Homozygous
The state of an individual having two identical alleles of a particular gene. When a person inherited two ‘blue genes’ for eye color, (s)he is homozygous for the eye color gene. Recessive traits only appear if an individual is homozygous for the corresponding gene. Compare to: heterozygous.
Hot spot
A sequence with a very high frequency of recombination (recombination hotspot) or mutation (mutation hotspot).
Housekeeping gene
A gene whose product is essential for most cells. For example, anything needed for RNA transcription or DNA replication.
Human genome project
An international effort to map and sequence all human genes. The project first began in 1990 and was declared completed in 2003, although work continues on certain aspects. The motivation behind the project was that sequencing and identifying all human genes would help us to better understand genetic disorders and find ways to diagnose, treat and perhaps prevent these conditions.
Huntington’s disease
An inherited brain disorder where there is a gradual loss of brain cells that cause symptoms like movement and walking problems, personality changes and intellectual decline. It is inherited in a dominant pattern which means that an individual who has Huntington’s Disease has a 50% (1/2) chance of passing the faulty gene to their child. There is currently no cure for Huntington’s.
I
In Vitro Fertilization (IVF)
A reproductive technology where sperm fertilize the egg in a laboratory dish and the fertilized eggs are put into a uterus for pregnancy to be established.
Incidence
The number of new cases of a condition that occur over a defined period of time. For example, the incidence of the birth defect ‘club foot’ is about 1 in 1000 live births. Compare to: prevalence.
Inherited
Passed down from parents to offspring through generations. The genes present in the parents are passed down to their offspring through egg or sperm cells. Traits may be inherited in different patterns such as x-linked inheritance, autosomal recessive or autosomal dominant inheritance.
Innate immunity
The basic resistance to disease or the first line of defence against infections. It is non-specific and doesn’t depend on previous exposure. Our skin is an important part and skin’s physical barrier and low pH inhibits microbial growth. Our body temperature can also be involved by inhibiting the growth of invaders and a fever will kill even more microorganisms.
Intracytoplasmic Sperm Injection (ICSI)
Intracytoplasmic sperm injection (ICSI) is a type of assisted reproductive technology (ART) that involves injecting a single sperm directly into the cytoplasm of the egg. This technique is often used to help overcome male infertility, in particular when the man has slow-moving, abnormally formed or low levels of sperm.
Intron
An area of DNA that is transcribed into RNA but does not code for a protein. Not all parts of RNA leave the nucleus and introns are the fragments that are cut out.
J
Junk DNA
An older (and now rarely used) term referring to noncoding DNA. These DNA segments were thought to be useless because their function was unknown however we are now beginning to understand that most of our ‘junk’ DNA is actually an important and crucial part of our genetic make-up.
K
Karyotype
The characteristic set of chromosomes for a particular species. Chromosome number, shape and size all determine the species’ karyotype. For example, humans have 46 chromosomes: two pairs each of chromosomes 1-22 and a pair of sex chromosomes.
L
Linkage
The tendency of two or more genes on the same chromosome to be inherited together. The closer two genes are on a chromosome, the more likely it is that they will be inherited together.
M
Marker
A segment of DNA that can be tracked from one generation to the next. Markers can be entire genes or a single letter of code (see polymorphism).
Meiosis
Cell division that results in cells that have half of the chromosomes of the original parent cell. Meiosis is the mechanism by which gametes are produced. Compare to: mitosis.
Mendel, Gregor
A monk who lived from 1822-1884 and developed the first understanding of the basics of genetics by conducting crossing experiments on pea plants. He provided a collection of experimental observations that were translated into generally applicable rules describing how simple genetic traits are transferred between generations.
Mendelian inheritance
A set of principles of inheritance first described by Gregor Mendel. In short, these principles state that alleles separate into gametes such that each gamete contains only a single copy of a gene (segregation). Furthermore, the alleles of different genes separate into gametes independently and do not sort based on the inheritance of other genes (independent assortment).
Messenger RNA (mRNA)
An RNA molecule which carries the message that acts as a template for translation into protein.
Metabolism
The complete set of chemical reactions that happen in an organism. Includes the conversion of food into energy, production of new cells and maintenance of existing cells.
Microarray (DNA)
A slide or membrane with small bits of DNA of known sequence fixed to it. Allows detection of genetic sequences by complementary binding of unknown DNA samples that are being tested.
Mitochondria
Organelles found in the cytoplasm of most eukaryotic cells and responsible for generating the energy for the cell.
Mitochondrial DNA (mtDNA)
A circular DNA molecule found inside each eukaryotic mitochondrion. Codes for most of the proteins needed by the mitochondrion.
Mitosis
Cell division that produces two daughter cells with chromosomes, and therefore DNA that is identical to the parent cell. Mitosis is the mechanism by which somatic cells are produced. Compare: meiosis.
Molecular chaperones
Proteins that assist in the correct folding or transport of other proteins. This helps to make sure that proteins are assembled properly and in the right place so they are useful to the cell.
Monosomy
The condition of missing one chromosome of a pair. In humans, this is usually lethal except in Turner’s syndrome where women have one X chromosome instead of the usual two X chromosomes. (Occasionally also used to refer to missing a part of a chromosome.)
Mosaic
An individual or tissue containing at least two cell lines that differ genetically but that have been derived from the same fertilized egg. Compare: chimera
Mouse model
A system that uses mice as the experiment/organisms to answer a question about biology. Mice are used because their genomes have been well studied. There are currently many mouse models available for research that mimic human diseases like obesity, cancer and neurological conditions like Huntington’s disease.
Multifactorial
Refers to a biological or physiological observation that is attributable to many factors. Fro example, some traits are determined by the interplay between genes and environment. Most common traits like skin colour and height are multifactorial. Although your genes give a rough estimate of your height, environment can also impact your height because if you don’t have adequate nutrition during childhood, you will likely not reach your height potential.
Mutation
A change in the DNA sequence of an organism that can have no effect, or be either beneficial or harmful.
N
Necrosis
Localized and premature death of cells in an organ or tissue due to disease or injury. Compare to: apoptosis.
Nucleic Acid
A large organic molecule made up of a chain of nucleotides. Examples include DNA and RNA.
Nucleoside
Organic compound made up of a purine or pyrimidine (base) joined to a sugar. Nucleosides are structurally very similar to nucleotides, but, unlike them, they do not contain a phosphate group.
Nucleotide
Organic compound made up of a purine or pyrimidine (base) joined to a sugar and a phosphate group. Nucleic acids (DNA & RNA) contain nucleotides linked together in long chains. Compare to: nucleoside.
Nucleus
A membrane-bound organelle containing the genetic material of a eukaryotic cell.
Nutrigenomics
The study of the interaction between diet, genes and environment and how they affect human health.
O
Oligonucleotide
A short fragment of single-stranded DNA that is typically 5-50 nucleotides long. Oligonucleotides can be primers to start PCR and also the fixed target in DNA microarrays.
Oncogene
A gene that, when mutated, can promote growth beyond the cell’s normal needs, thus leading to tumours. For example, a growth factor gene that is always expressed, even when there is no signal for growth, can cause a cell to grow beyond its normal limits. Compare: tumour suppressor.
Open Neural Tube Defect (ONTD)
A birth defect characterized by incomplete development of the spinal cord or the brain. The most common ONTD is Spina Bifida, a condition where the vertebrae do not fully enclose the spinal cord.
Operon
A segment of DNA containing linked gene that function in a coordinated manner, usually under the control of a single promoter.
Organelle
A sub-cellular structure in eukaryotic cells with specialized function. These membrane-bound compartments are sometimes compared to organs in the human body where each system has a different job. Examples include mitochondria, Golgi complex, endoplasmic reticulum, lysosome, peroxisome and the nucleus.
P
Penetrance
The proportion of individuals carrying a particular genotype that express the associated phenotype. Important for genetic diseases because complete penetrance means that 100% of people with the disease mutation will have the associated phenotype.
Phagocytosis
The process of a cell engulfing and eating particles or other cells.
Phenotype
The set of observable characteristics of an organism that are the result of its genotype and the environment.
Polygenic
Polygenic traits are affected by more than one gene. Phenotype variation in some traits is due to the interaction of many genes, each with a small additive effect on the character in question. For example, it is currently believed that there are 3 genes involved in the determination of skin colour.
Polymorphism
Literally: occurrence of different forms. This can mean different things depending on the field of study.
(Genetics) presence of variation in DNA sequence. For example: see SNP
(General Biology) presence of individuals with different phenotypes in a colony, population or species.
Preimplantation Genetic Diagnosis (PGD)
A technology that allows embryos created by in vitro fertilization to be tested for a genetic condition before transferring them to a uterus. PGD is an option for couples who are at risk of passing on a genetic condition. Once the embryo has grown to the 8-16 cell stage, one cell is removed and genetic testing is done. Only those embryos that are not affected with the genetic condition tested for are implanted.
Prevalence
The total number of existing cases of a disease or condition in a population at a specific point in time. For example, the World Health Organization estimates that over 177 million people have diabetes. Compare to: incidence.
Primer
A short nucleic acid chain that serves as a starting point for the copying of DNA (DNA replication). This short stretch of DNA or RNA is complementary to part of the DNA that is about to be copied, and binds to it to allow attachment of the other machinery needed (e.g. DNA polymerase) to copy the DNA.
Prokaryote
An organism that consists of cells which do not have membrane-bound organelles. Most prokaryotes are single-cleed organisms. Importantly, the DNA of prokaryotes is found loose in the cell rather than in a nucleus. Compate to eukaryote.
Promoter
A region of DNA located at the beginning (5’ end) of a gene. It contains sequences important in starting transcription. Mutations in the promoter region may cause incorrect expression of the gene and can lead to disease.
Protein
Large organic molecule made up of various combinations of amino acids. Proteins support living organisms’ shape and structure; carry messages within cells and between them; and as enzymes they regulate the chemical processes that sustain life.
Protein Synthesis
The process of building proteins by reading messages carried on mRNA and converting them to chains of amino acids using ribosomes and transfer RNA (tRNA).
Proteomics
The science that studies which proteins of the genome are expressed and when. Initially aimed at cataloguing the proteins present in a cell under various conditions, proteomics has joined up with genomics to try to understand how the expression of the genome enables all the complex functions of the cell to work.
Punnet Square
A Punnet Square is a diagram that illustrates the possible genotype combinations from a mating as determined by Mendelian Inheritance rules.
R
Recessive
Refers to an allele that is only expressed if another allele is not present.
Recombination
Reorganization, shuffling or other moving of genes from one place on a chromosome to another, or to a different chromosome. The most common example is crossing over.
Restriction Fragment Length Polymorphism (RFLP)
A size difference (length polymorphism) among fragments after DNA has been cut with restriction enzymes. Each cut piece is a restriction fragment and each fragment size is affected by DNA sequence. For example, if a target sequence is present, the restriction enzyme will cut the DNA molecule; if a target sequence is missing, the DNA won’t be cut and the fragment will consequently be longer. This characteristic has been important in creating lab tests for paternity and for DNA fingerprinting.
Ribonucleic Acid (RNA)
A long nucleic acid molecule found in the nucleus and cytoplasm of a cell. Similar to DNA, RNA consists a sugar-phosphate backbone with nitrogenous bases. RNA differs from DNA by having a different sugar in its backbone (ribose instead of deoxyribose); having uracil as a base instead of thymine; and functioning as a single-stranded molecule instead of a double-stranded helix. One function of RNA is to convert DNA to protein and there are three types of RNA that work together to achieve this task: mRNA, rRNA, and tRNA.
Ribosomal RNA (rRNA)
The RNA component of the ribosome. It associates with mRNA, tRNA and amnio acids during translation.
Ribosome
A complex of proteins and RNA that converts information from RNA into an amino acid chain. In other words: it translates the mRNA sequence into a protein.
Risk
The probability of a negative event occurring. For example, women have a 12% risk of developing breast cancer over their lifetime. The perception of risk can vary between different people. With our example, some people might think 12% is a low risk where as others might think it is a high risk.
S
Semidominant
Having an intermediate phenotype in an individual that has a heterozygous genotype for a particular trait. For example, degree of hair curliness is semidominant: if A represents curly hair, and a represents straight hair, an individual who has an Aa genotype would have wavy (i.e. not curly but not straight, rather intermediate) hair.
Sequencing
Reading of the components of a molecular chain of building blocks. For example, determining the order of nucleotides in a DNA or RNA chain or the amino acids within a protein.
Sex-linked traits
The tendency of certain characteristics to appear in one sex. Traits encoded by genes on one of the sex chromosomes (X or Y chromosomes in humans) can be expressed differently in males and females because males have an X and a Y chromosome, whereas females have two X chromosomes.
Single Nucleotide Polymorphism (SNP)
A variation in a single base (A, T, C or G) within a sequence of DNA. For any single base variation to be called a SNP it must be found in more than 1% of the population. So far more than 6 million SNPs have been discovered in the human genome. SNPs do not generally cause disease directly but some SNPs may indicate an individual’s susceptibility to disease or the response to drugs and treatments.
Soft Marker
A variation of normal fetal anatomy detected on ultrasound. Soft markers are not abnormalities and are seen in healthy, normal pregnancies but when a soft marker is seen, it increases the risk that there is a chromosome problem in the baby. For example, extra fluid behind a baby’s neck (called ‘nuchal translucency’) can be seen in healthy, unaffected babies but is more common in babies with a chromosome problem, such as Down syndrome.
Somatic Cell Nuclear Transfer (SCNT)
A laboratory method for creating clones of animals. SCNT requires 2 donors: a nucleus and an egg. The egg is stripped of its nucleus and the donor nucleus is placed inside. Because the donor nucleus is diploid, whereas normal egg cells are haploid, the egg is “tricked” into behaving as if it were fertilized. This leads the egg to divide and differentiate, resulting in an embryo that will develop into a copy (clone) of the organism that donated the nucleus.
Somatic Cells
The cells that form the body only. Unlike in germ cells, mutations or manipulations in these cells are not passed on to the next generation.
Spina Bifida
A condition where the bones of the spine (vertebrae) do not close properly around the spinal cord so part of the spinal cord is exposed and nerve damage occurs. The extent of damage depends on the size and location of the vertebrae gap. Spina bifida can occur alone or as part of a syndrome with other multiple birth defects. The exact cause of spina bifida is unknown. However, it is thought that both environmental and genetic factors play a role (multifactorial inheritance).
Sporadic
Rare or unpredictable. In genetics, specifically means that it is not known to be inherited. For example, if one person in a family had a genetic condition that was not found in any other family members, they may be referred to as having a sporadic case of that condition.
Stem Cell
A cell that has the ability to self-renew or divide indefinitely. Stem cells can also develop into other specialized cell types. There are several classifications: totipotent, pluripotent, and multipotent.
T
Telomere
A region of repetitive DNA at the end of a linear chromosome that serves to protect the end from deterioration or destruction. In somatic cells, with each round of cell division, telomeres get shorter and once they become too short to protect the ends of the chromosomes, cell division may be prevented, or cells may die.
Teratogen
A substance or exposure that causes birth defects. Many drugs, infections, chemicals and radiation can be teratogens.
Trait
A characteristic that an individual possesses. It could be a personality or behavior trait (like being warm and friendly), intelligence (a high IQ score) or a physical feature (like red hair or height). Genes may or may not have a determining role in a trait.
Transcription
The enzymatic process where complementary RNA sequences are created from DNA templates.
Transfer RNA (tRNA)
RNA responsible for bringing amino acids to the ribosome and working with the mRNA and rRNA to make an amino acid chain. tRNA transfers the amino acid to the growing protein chain during translation. Each tRNA molecule is specific to a certain amino acid.
Transgenic
Having a piece of DNA that originally stems from a different species. Transgenic organisms are a subset of Genetically Modified Organisms (GMOs).
Translation
The process of producing proteins from the information stored on an mRNA molecule. In other words it is the process of translating from the language of nucleotides to the language of proteins.
Translocation
The transfer of part of a chromosome onto another chromosome. Translocations may be balanced (having the right amount of chromosome material) or unbalanced (having too much or too little chromosome material). A reciprocal translocation is where a piece of one chromosome is exchanged for the piece of another chromosome.
Transposon
A segment of DNA that can remove itself from a chromosome and insert itself somewhere else in the genome, i.e. it can ‘jump’ from one place on a chromosome to another. Transposons can also move between organisms. They play a role in the transfer of antibiotic resistance among bacteria and can cause disease by creating mutations.
Triplet repeat expansion
Triplet repeats are 3 nucleotides that are repeated a number of times (e.g., TACTACTACTACTAC). Triplet repeat expansion is when extra repeats are added (e.g., more TACs). If this large repeat is within a gene, it can cause disease (e.g. Huntington’s disease).
Trisomy
The occurrence of an extra (third) chromosome in the total chromosome count of an individual. People typically have two copies (disomy) of all of their chromosomes. Often, having trisomy of a full chromosome is not compatible with life except for an additional chromosome 21 (Down Syndrome) or extra sex chromosomes.
Tumour Suppressor Gene
A normal gene that controls how often and how fast a cell divides. If both copies of a tumour suppressor gene are inactivated, the growth of the cell may go out of control and become a tumour.
U
Ultrasound
A technology that uses sound waves to create a picture. An ultrasound technician (sonographer) uses a hand-held wand (transducer) to direct sound waves at the internal body part of interest. The reflection or return of these waves creates a black/white image. Fluid appears black, solid material like bone appears white and other tissues, like most organs, appear as shades of grey.
V
Variable-Number Tandem Repeat (VNTR)
Catch-all term for repeats in the genome. Generally not associated with disease, these repeats are used in DNA profiling because the sequences vary in length between people. VNTR sounds complicated, but the phrase simply means, “repeats that vary in size”.
X
X chromosome
One of the two sex chromosomes. Women generally have two X chromosomes whereas men have one X chromosome and one Y chromosome.
Y
Y chromosome
One of the two sex chromosomes. Men generally have one X chromosome and one Y chromosome whereas women have two X chromosomes. The Y chromosome contains the genes that trigger male development and proper sperm formation.
Z
Zygote
A diploid cell that is the result of the fusion of a haploid egg and haploid sperm. The term zygote only applies before cell division starts (after which it is called an embryo).
