Glossary

A type of stem cell found in adult tissues, which is capable of dividing and multiplying to produce a range of different specialised cells. For example, bone marrow stem cells produce a wide range of different blood cells.

Alternate forms of a gene or DNA sequence (genetic variant) at a particular chromosome location.

For example, different alleles of the ABO gene on human chromosome 9 determine ABO blood type.

Refers to cells or tissues from different individuals.

In an allogeneic stem cell transplant, a patient is treated with donor stem cells from a healthy individual.

The principle of acting in the interest of others. In the context of gamete donation, this means the donor does not expect to receive a reward, financial or otherwise.

Small molecules that can be linked together to make proteins, which are large, complex biological molecules.

A test carried out during weeks 15-20 of the pregnancy, in which a small amount of the fluid that surrounds the fetus is removed for biochemical or genetic testing. It can assess whether the fetus could develop, or has developed, an abnormality or serious health condition.

Androgens are hormones which govern the development and maintenance of male characteristics. Testosterone is the best known of these in humans.

Androgens are also present in females and play a role in reproduction in both sexes.

An abnormal number of chromosomes, either too few or too many. Nearly all human body cells usually have a set of 46 chromosomes, while egg and sperm cells have 23.

A gamete donor whose identity is not known to the recipient or to the resulting donor-conceived person.

Most gamete donors who donated before 1 April 2005 at licensed clinics in the UK are anonymous. Some anonymous donors have chosen to reregister as identifiable donors.

The placing of sperm, inside the vagina or uterus, for the purpose of conception, without sexual intercourse.

In genetic epidemiology, an association is the observed connection between a trait and a particular version of a gene or other genetic variant.

Genome-wide association studies (GWAS) are used to pinpoint variants associated with complex disorders or traits, which are caused by the interaction of multiple genetic and non-genetic factors.

Refers to cells or tissues from the same individual. In an autologous stem cell transplant, a patient is treated with their own healthy stem cells.

A pattern of inheritance in which a single mutated copy of a gene is sufficient to cause an observable disorder or trait, for example, the mutation that causes Huntington's disease.

Also known simply as dominant inheritance.

A pattern of inheritance in which a mutation must be present in both copies of a gene in order to cause an observable disorder or trait, for example the mutation that causes cystic fibrosis.

Also known simply as recessive inheritance.

Any chromosome apart from the sex chromosomes. In humans there are 22 pairs of autosomes, numbered 1-22, and a pair of sex chromosomes.

A pair of complementary bases (chemical units that form DNA) in a double-stranded nucleic acid molecule.

In DNA, the base adenine (A) always pairs with thymine (T) and the base cytosine (C) always pairs with guanine (G).

Chemical units that form part of DNA and RNA. DNA contains the bases adenine (A), cytosine (C), guanine (G) and thymine (T). In RNA, the thymine is replaced by uracil (U).

A storage facility used to archive biological samples for use in research. Ranging in size from individual refrigerators to warehouses, biobanks are maintained by institutions such as hospitals, universities, nonprofit organizations, and pharmaceutical companies.

The industrial application of biological processes and living organisms to make products for human use, especially in medicine, agriculture and food science.

A mammalian embryo in the first stage of development, when the fertilised egg has grown into a hollow ball made up of a few hundred cells.

Cells produced by the division of the zygote.

A gene on human chromosome 17, which instructs the cell to make a protein that normally helps to repair damaged DNA and suppress cell growth.

A person who inherits certain mutations in a BRCA1 gene has a higher risk of getting breast cancer and certain other types of cancer.

A gene on human chromosome 13, which instructs the cell to make a protein that normally helps to repair damaged DNA and suppress cell growth. A person who inherits certain mutations in a BRCA2 gene has a higher risk of getting breast cancer, ovarian cancer and certain other types of cancer.

A cancer that forms in tissues of the breast. Breast cancers occur in both women and men, although male breast cancer is rare.

A group of diseases that start when the signals that control how much and how often cells divide stop working properly. This causes cells to grow and multiply too much, and eventually to invade other tissues.

A person who carries a gene mutation that can cause a genetic condition.

The carrier may be unaffected by the genetic condition, but can pass on the mutated gene to their children, who could be affected.

CRISPR Associated Proteins are enzymes that associate with CRISPR RNAs to bind to and alter DNA or RNA target sequences.

Cas enzymes originate in bacteria and as such a wide variety of types exist. Some are used for genome editing or editing RNA.

There are also versions that have been altered in the lab to perform specific tasks. Common examples include Cas9 which makes a double-stranded break in a target DNA sequence, and Cas13 which targets RNA.

Set up by the Health and Social Care Act 2012, CCGs are responsible for the commissioning of most hospital and community NHS services in local areas. CCGs replaced Primary Care Trusts from April 2013 and are overseen by NHS England. All GP practices now belong to CCGs.

Cells are the building blocks of all living things. A human body is made up of around 100 trillion cells (100 million million).

cfDNA (circulating DNA or cell-free DNA) are fragments of DNA that are released into the blood.

Elevated levels are seen in cancer and they can be detected using 'liquid biopsies' to aid diagnosis. Fetal cfDNA can be detected in maternal blood through non-invasive prenatal testing.

An organism (or tissue) composed of a mixture of genetically distinct cells, formed by processes such as fusion of early embryos, grafting, or mutation.

A chromosome abnormality caused when a part of one chromosome swaps place with, or becomes attached to, another chromosome. Translocations can be balanced (there is no loss or gain of genes) or unbalanced (there is loss or gain of genes).

Chromosomes are tightly packaged bundles of DNA, the chemical that encodes genetic information. Nearly all human body cells have a set of 46 chromosomes, while egg and sperm cells have 23.

A research study in which new ways to prevent, detect, diagnose, or treat disease are tested on human participants.

An exact genetic replica of a living thing. Clones may occur naturally or, in the case of cloned animals and plants, be produced in the laboratory using somatic cell nuclear transfer technology.

In cell biology a clone can be any of a group of identical cells derived from the same cell.

CNR (cell nuclear replacement) is technique in which the genetic material (DNA) from an egg cell is replaced with that of an adult or embryo body cell of the same animal species. Also referred to as somatic cell nuclear transfer (SCNT), or popularly as 'cloning'.

CNV (copy number variation) refers to segments of DNA larger than 1kb (1000 base-pairs) that vary in copy number between individuals. CNVs that encompass one or more genes can influence susceptibility to disease and other traits.

Coding DNA sequences are the portions of a gene that encode ('code for') a protein or RNA molecule.

Complex diseases are caused by the interaction of multiple genetic, environmental, and lifestyle factors.

Examples include type 2 diabetes and cardiovascular disease.

Present from birth. A congenital condition may or may not have a genetic basis.

When two individuals share genetic material as the result of them being descended from a common ancestor, e.g. first cousins.

Clustered regularly-interspaced short palindromic repeats.

Naturally occurring in bacteria, segments of DNA used for defence against pathogens.

Used by humans in genome editing: the CRISPR/Cas system used to edit DNA at specific locations in the genome.

A genome-editing platform that uses an enzyme (Cas9) to make a double-stranded break at a specific location in the genome, directed by a guide RNA.

CVS (chorionic villus sampling) is a test carried usually carried out between the 11th and 14th week of pregnancy, in which a few cells of the placenta are removed for biochemical or genetic testing. This is most commonly to check a fetus for conditions such as Down’s syndrome and other chromosomal or genetic disorders.

The study of chromosomes, usually to detect changes in their number or structure associated with a medical condition.

The jelly-like material present inside a eukaryotic cell - for example, plant and animal cells - that surrounds the nucleus.

A UK charity established in 1993 which supports donor-conceived people, their families, and people considering or undergoing donor-assisted conception treatment.

A person conceived through gamete provision.

A name given in 2013 to a voluntary information and contact register that enables donor-conceived people, their donors and their half-siblings to exchange information and (where desired) contact one another. The register is for anyone over 18 who donated or was donor-conceived in the UK prior to August 1991.

A type of mutation in which a section of DNA is missing.

The insertion of a donated sperm sample into a woman's vagina, cervix or womb to achieve a pregnancy.

DNA (deoxyribonucleic acid) is the molecule that encodes genetic information. It contains four different chemicals, or bases, known as A, C, G and T.

Genes and chromosomes are made of DNA.

A DNA (genetic) marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species.

A laboratory technique used to match samples of DNA (for example in forensics) or to establish the relationship between two people (for example in paternity testing).

Determining the order of chemical bases (known as A,C, T and G) in a DNA molecule.

A biochemical process in which a DNA molecule is modified by the addition of methyl chemical groups at selected locations. It is important in the control of gene expression and embryonic development in higher organisms.

A pattern of inheritance in which mutation in only one copy of a gene is sufficient to cause an effect, for example the gene that causes Huntington's disease.

An administrative reference number used by clinics to track the use of an individual donor's eggs or sperm. Some people use these codes to help them find genetic siblings, using contact networks and groups that aim to support donor-conceived people, their families, and donors. Whereas the USA's Donor Sibling Registry facilitates and confirms connections primarily by using donor codes, neither UK clinics nor the Human Fertilisation and Embryology Authority are currently permitted to release such codes. Instead, people who were donor-conceived in the UK can seek siblings via Donor Sibling Link.

A form which must be completed for all UK gamete donors, requiring information to confirm the donor's identity, physical characteristics, ethnic background and medical history. The donor can write a personal description (pen portrait/picture), provide their reasons for donating, and add a goodwill message. The non-identifiable information contained in this form can, upon request, be made available to patients requiring donation, to parents of children conceived with the donor's gametes, and to children conceived with the donor's gametes (once the latter reach the age of 16). When children conceived with the donor's gametes reach the age of 18, the full content of this form can be made available to them on request.

The 3D structure of DNA, the chemical that encodes genetic information. Two strands of DNA stick together into a 'twisted zip' structure, in which pairs of chemical bases (A-T and C-G) make up the teeth of the zip.

A service established by the Human Fertilisation and Embryology Authority in 2010, which enables donor-conceived people aged 18 or over to consent to be put in touch with their genetic siblings.

A US-based non-profit organisation established in 2000 which facilitates searching for, and establishing contact between, people who are genetically related as a result of gamete donation. It is open to a global membership of donor-conceived people, their families, and donors.

A duplicated portion of genetic material - either a gene, section of DNA, or piece of chromosome.

A mature female reproductive cell, which contains half the genetic information needed to make a new human. Also known as an oocyte.

A stage of development which, in humans, lasts for eight weeks after the fertilised egg first starts to divide.

A gene is said to encode (or 'code for') a protein when the information (DNA) in the gene is translated into that particular protein.

Is a condition where the endometrial lining grows outside the uterus, often affecting the functioning of the uterus and ovaries.

The endometrium in the inner-most layer of the uterus, and is the site of implantation for an embryo. It contains a layer of stem cells to regenerate the layer that thickens and is shed during the menstrual cycle.

Proteins produced by a living organism which act to bring about, or increase the rate of, a specific biochemical reaction.

The science of enduring (but ultimately reversible) changes in the pattern of gene activity, during embryo development and beyond, that do not involve alteration of the DNA sequence. These changes occur in response to conditions within the embryo and more generally.

The total epigenetic (heritable, non-DNA-sequence based changes to gene expression) modifications that have been added to an organism's genome.

A type of stem cell found in early embryos, which is capable of developing into all (totipotent) or a wide range of (pluripotent) different body tissues.

Seeking to change a population, to increase the occurrence of chosen characteristics that are believed to be both heritable and desirable.

An organism consisting of a cell or cells in which the genetic material is DNA packaged into chromosomes, and contained within a distinct nucleus. All animals, plants and fungi are eukaryotes.

The portion of a genome that codes for RNA and protein production.

The segment(s) of a gene that contain the information coding for a protein. In a gene, exons are interspersed with introns which do not encode the protein sequence but may contain regulatory information.

Fallopian tubes extend from the ovaries to the uterus, and are the site of fertilisation during natural conception.

The Food and Drug administration is a US federal agency responsible for protecting public health. It is the body responsible for regulation and approval of drugs and other pharmaceutical products such as vaccines within the USA.

The fusion of male and female gametes to form a zygote.

The unborn offspring of a mammal. In humans, this stage of development lasts from nine weeks after fertilisation until birth.

A laboratory technique that uses fluorescent-labelled pieces of DNA to detect specific genes, chromosome segments or chromosomes, in cells examined under a special microscope.

The ovarian follicle is the anatomical structure inside which an oocyte (egg cell) develops. Once a month, a single follicle (occasionally more than one) will mature and the egg cell is released.

A reproductive cell, either the male sperm or the female egg.

The basic biological unit of inheritance. Genes are made out of DNA, and are coded instructions for making proteins or RNA molecules.

Gene expression is the process of converting the information contained in a gene into the gene product. The DNA of the gene is first transcribed into RNA, which is then either translated into a protein or remains as an RNA molecule. The expression level of a particular gene can be turned ’up’ or ‘down’ in different cells at different times, as required.

A patent on a specific gene sequence, its chemical composition, and/or processes for obtaining or using it.

The use of genetic material (DNA or RNA) as a medical treatment to either: replace (or repair) a faulty or missing gene product; switch off production of a harmful gene product; or destroy specific cells involved in disease.

A condition or illness caused by changes (mutations) in a gene or genes.

Information and advice given to patients and their relatives affected by, or at risk of, a genetic condition. An explanation of risks and options may include the findings of specific genetic tests.

The alteration of an organism's or a cell's genetic material using biotechnology techniques. Traditionally, the term has referred only to alterations involving the introduction of transgenic (foreign) DNA.

Increased probability - compared to the general population - of developing a disease, due to the presence of one or more gene mutations.

A test that uses genetic analysis to diagnose or predict an illness or condition.

A relatively common (present in more than 1% of the population) alternative version of a DNA sequence. Some variants are associated with particular traits and disorders, but many have no observable effect on appearance or health.

The total genetic information of an organism. A complete copy of the genome is found in most body cells.

Making deliberate alterations to the DNA sequence at targeted locations in the genome. This can include deleting, inserting or replacing sections of DNA. Several approaches are used to achieve these changes, include zinc finger nucleases (ZFNs), TALENs, CRISPR/Cas and base editing.

A genome-wide association study examines the whole genomes of a large number of individuals, to identify genetic variants associated with a trait or risk of a disorder.

Using genetic information to determine disease risk and predisposition, diagnosis, likely outcomes, and to help select and prioritise possible treatments.

The specific DNA sequence present at a particular chromosome location.

Egg and sperm cells (also known as gametes) and their precursors.

Relating to genetic information that can be inherited by the next generation (the DNA in egg and sperm cells, and their precursors).

A collection of specific alleles (particular DNA sequence variants) located in a cluster on a chromosome that are likely to be inherited together.

An international project that examined genetic variation in people from around the world, to speed the search for genes linked to common diseases. The scientists identified clusters of genetic variants - single nucleotide polymorphisms (SNPs) - that have been inherited together in a 'haplotype block' over many generations.

The extent to which a particular trait is inherited. Studies of heritability typically estimate the proportion of observed variation in a particular trait (for example, height) that can be attributed to inherited genetic factors in contrast to environmental ones.

Having inherited two different alleles (alternate versions of a gene or DNA sequence), one from each parent.

When referring to genetic disorders, a heterozygote is usually someone who has one disease and one non-disease allele.

A UK non-departmental public body established by an Act of Parliament in 1990, which regulates treatment using eggs and sperm, and treatment and research involving human embryos. It sets standards for, and issues licences to, fertility treatment and embryo research centres.

Having inherited two different alleles (alternate versions of a gene or DNA sequence), one from each parent. When referring to genetic disorders, a heterozygote is usually someone who has one disease and one non-disease allele.

A chemical messenger produced in the body, for example testosterone. Hormones can travel through the blood and have an effect elsewhere in the body.

An international scientific research project with the goal of determining and decoding the total sequence of human DNA. It was declared complete in 2003.

A progressive neurodegenerative genetic disorder, which affects muscle coordination and some cognitive functions.

ICSI (intracytoplasmic sperm injection) is a variation of in-vitro fertilisation (IVF). During ICSI, a single sperm is injected directly into an egg, in order to fertilise it.

The process by which certain mammalian genes are switched off during early embryo development, according to whether they were inherited from the father or mother.

Latin for 'within the glass'. Refers to experiments performed in a controlled environment like a test tube or culture media, rather than inside a living organism or cells.

Latin for 'within the living', referring to processes taking place within a living organism.

The addition of one or more nucleotide base pairs into a DNA sequence. Insertions into the coding region of gene (insertion mutations) often stop the gene working.

Integrated Care Boards run Integrated Care Systems, which are responsible for commissioning health and care services across England as of 1 July 2022, replacing Clinical Commissioning Groups. They must be made up of at least five executive directors, plus three non-executives.

Integrated Care Systems are responsible for bringing together NHS bodies including hospital trusts, local councils and others to provide health and care services for the local population within a fixed budget. There are 42 ICSs, run by Integrated Care Boards, which were introduced as part of the Health and Care Act in May 2022 and they superseded Clinical Commissioning Groups on 1 July 2022.

Creations of the mind to which individuals or organisations are granted exclusive rights, as defined in and protected by law. Those who are granted such rights are said to be the owners of the intellectual property.

A medical procedure during which a thin tube is put into the vagina and through the cervix, to allow sperm to be placed directly in the uterus.

Non-coding parts of a gene that are 'edited-out', and so do not contribute to making the final protein or RNA product of the gene. Introns are scattered between the exons of a gene.

A type of chromosome rearrangement in which a section of chromosome is removed, turned upside down, and reinserted back into its place in the chromosome.

A cell with similar properties to an embryonic stem cell, but created in the laboratory by 'reprogramming' cells from adult tissues, such as skin cells.

IVF (in vitro fertilisation) is a treatment for infertility, in which eggs are removed from a woman's body, fertilised with sperm in a laboratory, then returned to the womb shortly afterwards to continue developing.

The full or partial creation of gametes (egg or sperm cells) outside the body.
This often, but not always, means creating gametes from stem cells.

A gene mapping test used to identify genetic and chromosomal abnormalities in embryos.

The number, appearance and banding pattern subsequent to chemical staining, of chromosomes in the nucleus of a eukaryotic cell. Also used to describe the complete set of chromosomes in an organism.

A method for determining the number of chromosomes and detecting chromosomal abnormalities of an individual. Carried out by analysing a photograph of the chromosomes of a single cell cut out and arranged in pairs based on their size and banding pattern after chemical staining.

A knockout is a laboratory animal in which researchers have inactivated, or 'knocked out,' an existing gene by replacing it or disrupting it with an artificial piece of DNA.

A genetic technique used to track the inheritance of a genetic condition through a family, using genetic markers closely linked to the suspected disease gene.

A location on a chromosome (plural loci). A variant in the DNA sequence at a particular locus is called a gene allele.

The form of cell division by which egg and sperm cells are formed. Unlike normal cell division (mitosis), the number of chromosomes in the resulting cells is half that in the original cells.

A pattern of inheritance displayed by a trait under the control of one gene, akin to the patterns of inheritance described by the nineteenth-century scientist and priest Gregor Mendel.

Metastasis is the spread of cancer cells to new areas of the body. A metastatic cancer, or metastatic tumour, is one which has spread from the primary site into different areas of the body.

The biochemical process by which methyl groups are added to another chemical group or molecule. Methylation of DNA at specific locations in the sequence is a form of epigenetic regulation.

An array of many different pieces of DNA, arranged on a small piece of glass, silicon or other solid material. Microarrays can be used to study thousands of different genes or genetic variations at the same time.

MicroRNAs are small, non-coding RNA molecules that regulate gene expression by suppressing the RNA pathway that translates genes into protein. They act like 'master switches', having the ability to control the activity of multiple genes.

Repeated sections of DNA, two to five base-pairs in length, found scattered throughout the human genome. Because they are highly variable in length, microsatellites are often used in genetic studies, and in forensic and paternity tests.

Energy-generating structures found in the cells of all multicellular organisms. They contain a few genes, which mainly make proteins involved in energy metabolism.

A reproductive option that was developed for the purpose of avoiding the transmission of mitochondrial disease from mother to child. It involves creating an embryo using nuclear DNA from the prospective parents, and mitochondria (including mitochondrial DNA) from a donor. It is sometimes referred to as MDT (which stands for 'mitochondrial donation treatment') or as MRT (which can stand for either 'mitochondrial replacement therapy' or 'mitochondrial replacement techniques'). There are also specific mitochondrial donation techniques that have their own acronyms.

Unusual patterns of inheritance related to mutations in genes found in the mitochondria. Mitochondrial DNA is always maternally inherited, since sperm contribute no mitochondria when they fertilise the egg.

The ordinary form of cell division, in which a cell divides to produce two new cells that both have the same number of chromosomes as the original cell.

The smallest particle of a substance that has all of the physical and chemical properties of that substance. Molecules are made up of two or more atoms - for example, a molecule of water is made up of two atoms of hydrogen and one of oxygen.

Involving, or controlled by a single gene. Monogenetic conditions include Huntington's disease and cystic fibrosis.

The presence of only one chromosome from a pair in an individual. With the exception of sex chromosomes (eg Turner syndrome), monosomies frequently have severe effects, usually resulting in early miscarriage.

The occurrence of two or more cell populations within a single tissue or individual, which have different genetic constitutions.

mRNA (messenger RNA) is an intermediate stage between a gene and the protein it codes for. The cell uses an mRNA template when making a protein, rather than reading the DNA code directly.

Genetic information located within mitochondria, the cell's energy generators, rather than in the nucleus. Mitochondrial DNA is inherited solely through the maternal line, as sperm contribute no mitochondria to the fertilised egg.

A change in the sequence of DNA. Mutations occurring in genes may prevent them from working properly, which might result in disease (a genetic condition). Mutations occur naturally at a low rate, but can also be induced by radiation and some chemicals.

Neurodegenerative disease is an illness caused by the progressive loss of structure or function of neurons (nerve cells), including death of neurons for example motor neurone disease or Alzheimer's disease.

The National Health Service (NHS) is a publicly funded healthcare system in the United Kingdom.

A public body that develops and provides guidance to UK healthcare professionals and others, to ensure that the care they provide is of the best possible quality and offers the best value for money.

Test for chromosomal conditions such as trisomies in the fetus by assaying fetal cfDNA in the mother's blood. Because the test assays chromosomes it can also detect fetal sex.

Noncoding DNA is a DNA sequence that does not encode ('code for') a protein or RNA molecule. These sequences may play a role in gene regulation or may be structural within the chromosome.

Nucleotides are the building blocks that make up DNA and RNA molecules. A single nucleotide consists of a nitrogenous base (adenosine, cytosine, guanine, or thymine in DNA), a phosphate group, and a sugar molecule.

The structure within a eukaryotic cell that contains the vast majority of its genetic information.

Unintended changes to a genome, away from the desired target site, which occur as a consequence of genome editing.

Ovarian hyperstimulation syndrome is a medical condition that can occur as a side effect of fertility treatment and IVF. It is often mild but can occasionally be severe and even fatal.

A mature female reproductive cell (egg cell), which contains half the genetic information needed to make a new human.

An artificially grown mass of cells or tissue that resembles an organ.

Cancer that forms in tissues of the ovary (one of a pair of female reproductive glands in which the ova, or eggs, are formed).

One of a pair of two female reproductive organs, which produce eggs and hormones.

A form of asexual reproduction where growth and development of embryos occur without fertilisation.

An embryo created through parthenogenesis.

A form of intellectual property. The owners of a patent are granted a temporary monopoly over an invention (a right to exclude others from making, using or selling it) in exchange for detailed public disclosure of the invention

Microorganisms that can cause disease, such as bacteria or viruses.

PCR (polymerase chain reaction) is a technique used for making millions of copies of a particular piece of DNA, requiring only a tiny sample of starting material.

A Primary Care Trust is an English National Health Service (NHS) organisation that provides some primary care (e.g. doctor's surgery/office) and some community (e.g. community nursing) services.

A diagram of the genetic relationships and medical history of a family, which uses standard symbols to represent affected and unaffected males and females.

The extent to which a mutation causing a particular disorder causes clinical symptoms of that disorder. This usually refers to autosomal dominant conditions.

An approach to medicine based on grouping patients according to the characteristics of their disease or how they respond to particular treatments (or to prophylaxis). This enables the identification and development of measures that are most effective for particular groups of patients.

A technique that can enable people to avoid passing gene mutations, and therefore disease predisposition, on to their children. It involves testing the genes of embryos created through IVF.

Also known as PGT-M: preimplantation genetic testing for monogenic disorders.

PGS (preimplantation genetic screening) is a test that can be carried out on IVF embryos, to ensure that only embryos with no obvious chromosome conditions are returned to the woman's womb. Also known as PGT-A (Preimplantation Testing for Aneuploidy).

A group of techniques that look at the genetic material of embryos created through IVF. These include:

PGT-A: preimplantation genetic testing for aneuploidy – also known as PGS (preimplantation genetic screening)

PGT-M: preimplantation genetic testing for monogenic conditions – also known as PGD (preimplantation genetic diagnosis)

PGT-SR: preimplantation genetic testing for structural chromosome rearrangements

PGT-P: preimplantation genetic testing for polygenic risk scores

A technique that can enable people to avoid passing gene mutations, and therefore disease predisposition, on to their children. It involves testing the genes of embryos created through IVF. Also known as PGD: preimplantation genetic diagnosis.

An area of research that aims to develop ways of matching medicines to a person's genetic makeup, to avoid adverse reactions or non-response to particular drugs.

The physical characteristics of an organism, as distinguished from its genetic make up (genotype).

Describes a cell capable of developing into any type of cell or tissue except those that form a placenta or embryo.

A trait disorder is one affected by the combined effects of multiple different genes.

Genetic polymorphism (see also SNP and genetic variant) refers to a natural variation in a gene, piece of DNA, protein, or chromosome which may be associated with a particular trait or disease, or may have no effect on the development of the individual.

Increased likelihood of developing a particular disease due to carrying one or more gene mutations and/or having a family history that indicates an increased risk of the disease. Also called genetic susceptibility.

A biochemical, genetic or ultrasound test performed during pregnancy, to determine if a fetus is affected by a particular disorder.

A simple organism, usually single-celled, which lacks a cell nucleus and other membrane-bound compartments. All bacteria are prokaryotes.

Treatment given with the intention of preventing disease, before symptoms of disease appear.

Cancer that develops in the prostate (a gland that forms part of the male reproductive system).

A large biological molecule made up of a string of sub-units called amino acids. There are thousands of different proteins in the human body, each with a particular job. For example, haemoglobin carries oxygen around the blood.

A pattern of inheritance caused by a gene mutation that only has an observable effect if two mutated copies are inherited, for example, the mutations in the CFTR gene that cause cystic fibrosis.

The creation of new DNA molecules using fragments of DNA from different sources, which can be used to make genetically modified organisms.

The process by which two DNA molecules exchange genetic information. In meiosis, exchange can take place between maternal and paternal chromosomes leading to a novel combination of genetic material in the egg or sperm.

The production of an exact genetic replica of an animal, either by splitting an early embryo, or by using a technique known as somatic cell nuclear transfer to clone a body cell taken from an adult or embryo.

RNA (ribonucleic acid) is created when DNA is transcribed. Like DNA, RNA contains the chemical bases adenine (A), cytosine (C) and guanine (G), but uses uracil (U) instead of thymine (T).

A naturally-occurring cell process that may be exploited as a way of selectively shutting down gene activity for therapeutic purposes. This involves injecting cells with short, specific pieces of RNA, which then trigger the breakdown of a particular messenger RNA molecule.

A stem-cell-based embryo models (SCBEM) is a coherent multicellular structure that – in some respects – resembles an embryo in the earliest stages of development.

SCBEMs are created in the laboratory from stem cells, rather than from eggs and sperm.

SCNT (somatic cell nuclear transfer) is a technique in which the genetic material from an egg cell is replaced with that of an adult or embryo body cell of the same animal species. Also known as cell nuclear replacement (CNR), or popularly as 'cloning'.

Assessing a group of people to determine who among them is at particular risk of having or transmitting a disease or health problem. In the context of UK gamete donation, screening of gamete donors is legally required, in order to assess the risk presented by HIV and Hepatitis B and C. Additional tests may be required depending on the donor's circumstances, in accordance with current professional guidelines.

The order of the chemical units (bases) along a piece of DNA or RNA.

One of the two chromosomes (X and Y) that determine the sex of an individual.

A disorder caused by a mutation in a single gene. For example, cystic fibrosis which is caused by mutations in the CTFR (cystic fibrosis transmembrane conductance regulator) gene.

An SNP (single nucleotide polymorphism) is a single chemical unit (base pair) variation in a stretch of DNA, present in more than 1% of the population. A common SNP is estimated to occur 1 in every 1000 base pairs between any two people.

Relating to genetic information that cannot be inherited by the next generation (all body cells apart from egg and sperm cells, and their precursors).

A mature male reproductive cell, which contains half the genetic information needed to make a new human.

An immature sperm cell, produced in the testis, which will develop into sperm. Like sperm, spermatids have half the genetic information necessary to produce offspring.

The removal of introns from the messenger RNA copy of a gene, so that only the gene exons are present in the final version.

A cell that can multiply and give rise to a variety of other, more specialised cell types. For example, stem cells in the bone marrow make many different blood cells.

The practice of bearing a child for another person or couple. In gestational (also known as 'full' or 'host') surrogacy, the surrogate carries an embryo conceived through IVF. In traditional (also known as 'partial' or 'straight') surrogacy, the surrogate's own egg is fertilised with the intended father's sperm.

Protective DNA-protein structure at the ends of linear chromosomes. In most tissues, telomeres shorten every time a cell divides and copies its genetic information.

Able to disturb the growth and development of an embryo or fetus

The male reproductive organs, which produce sperm and hormones.

A popular name for the proposed use of embryo stem cells, derived using somatic cell nuclear transfer technology, to develop genetically-matched cell therapies for a range of diseases.

A test carried out to determine what combination of a particular set of genetic markers (termed HLA markers) a person has inherited. This procedure can be carried out on IVF embryos, to establish potential tissue compatibility for donating umbilical cord blood to a sibling.

Describes a cell capable of developing into any type of cell or tissue, including extraembryonic tissues, such as the placenta. The zygote, formed immediately after fertilisation, is totipotent and has the potential to create an embryo.

A distinguishing characteristic or quality of an organism.

The process by which DNA is 'read' to produce RNA molecules. These can have regulatory functions, or may be mRNA molecules that pass from the cell nucleus to the ribosomes, where they are used as a template to build proteins in a process called translation.

A transcription factor is a protein that binds to a particular DNA sequence in order to control the rate at which a nearby gene is transcribed and expressed.

The transcriptome encompasses all of the RNA molecules in a sample - be that a whole organism or a single cell. It includes messenger RNA and noncoding RNA and can be different in different body tissues and at different times according to which genes are active when the sample is taken.

Describes a living thing that contains genes from another creature. Transgenic animals are bred in the laboratory, by genetically altering a newly fertilised egg.

The presence of an extra chromosome, resulting in a total of three chromosomes of a particular type instead of a pair - for example, trisomy 21, which causes Down syndrome.

A distinct mass of tissue which results from an abnormal growth or abnormal division of cells. Tumours are said to be cancerous if they tend to continue growing uncontrollably, and if they are thought to have the potential to spread to surrounding tissues.

A government-funded project to collect DNA samples and medical records from 500,000 British volunteers aged 45-69, to study the effects of genetic and environmental factors on health.

A hollow reproductive organ in a woman's pelvis, where an embryo can implant and develop throughout gestation. The fallopian tubes connect the uterus to the ovaries.

A delivery system used in the laboratory to carry foreign DNA into a cell. Modified viruses are commonly used as vectors in gene therapy.

A tiny infectious particle that can invade a cell.

Section 13(5) of the UK's Human Fertilisation and Embryology Act 1990, amended by the Human Fertilisation and Embryology Act 2008 requires that:

'A woman shall not be provided with treatment services, other than basic partner treatment services, unless account has been taken of the welfare of any child who may be born as a result of the treatment (including the need of that child for supportive parenting), and of any other child who may be affected by the birth.'

The Human Fertilisation and Embryology Authority (HFEA) is required provide guidelines for IVF clinics on how to implement this rule.

Determining the order of every base in an organism's genome. Differs from genotyping, which only looks at a specific subset of genetic variants.

One of two sex chromosomes that determine biological sex. Human females have two X chromosomes, whereas males have one X and one Y chromosome.

The process by which one of the two X chromosomes present in females is randomly inactivated in the cells of the early embryo.

A pattern of inheritance in which a mutation in a gene on the X chromosome causes an observable effect (1) in males, who only have one copy of the gene mutation because they have only one X chromosome; and (2) in females who have two mutated copies of the gene, one copy on each of their two X chromosomes. Haemophilia is an example of a genetic condition with an X-linked recessive inheritance pattern.

The transplantation of living cells, tissues or organs from one species to another, for example the transplantation of animal organs into human patients.

One of two chromosomes that determine biological sex. Human males have an X and Y chromosome, whereas females have two X chromosomes.

The single cell formed immediately after fertilisation, once the genetic information of the egg and sperm have fused.