Genetic Terms

Biopsy
A biopsy is a medical procedure that involves taking a tissue specimen for diagnosis.

Breast Cancer
Breast cancer is the uncontrolled growth of malignant breast tissue. It is currently the most common cancer in women and the leading cause of cancer-related death in the 15-54 age group.

Carrier
Carrier usually refers to an individual who carries one copy of a mutated, disease-causing gene. A carrier of such a gene usually shows no symptoms of the disease but can pass the mutant gene on to his or her children. If both parents are carriers, there is a one-in-four chance that their child will be affected by the disease.

Fanconi Anaemia
A rare genetic disorder found in children. It is characterised by progressive bone marrow failure, skeletal deformities and a predisposition to leukaemia.

Genetics
Genetics is the scientific study of heredity, the passing of specific traits from one generation to the next.

Cells
Cells are the individual units that make up all the tissues of the body.

Chromosomes
Chromosomes are the structures within cells that carry the genetic information in the form of DNA. Each chromosome is composed of a single, long molecule of DNA, packaged with proteins. Humans have 46 chromosomes in each cell, except in the egg cell and sperm cell, in which there are only 23.

Cystic fibrosis
Cystic fibrosis is a serious genetic disease that affects almost all the mucus-producing glands of the body. It is caused by a single gene defect that results in the lungs, pancreas, intestines and other organs getting clogged up with thick, sticky mucus.

DNA
DNA (deoxyribonucleic acid) is the major store of genetic information in a cell. A DNA molecule consists of two strands held together, in the shape of a double helix, by weak bonds between base pairs of nucleotides. Each strand of DNA consists of nucleotide subunits that each contain one of 4 bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The DNA sequence of bases encodes specific information of an individual's genetic blueprint.

Nucleotide
A nucleotide is a subunit of DNA or RNA consisting of a base (adenine, guanine, thymine or cytosine in DNA; adenine, guanine, uracil or cytosine in RNA), a phosphate molecule, and a sugar molecule. The nucleotide units are joined together via their sugar-phosphate groups to make up a DNA or RNA molecule and its sequence is described as the sequence of its bases, e.g. AAAAGTTCGTCTAGGTC. The two strands of a DNA molecule are held together as a double helix by weak bonds between base pairs: adenine and thymine, or guanine and cytosine.

Genome
The genome is the term used to describe all of the genes stored in the chromosomes of a particular organism; its size is generally given as its total number of base pairs. The human genome contains about three billion base pairs.

Gene
Genes are the fundamental physical and functional unit of heredity. A gene is an ordered sequence of nucleotides, located in a particular position on a particular chromosome that directs the synthesis of a specific functional product, like a protein or RNA molecule. To exert its affect in a cell, the coding region of a gene is transcribed into messenger RNA and then translated into protein. A few genes are transcribed but not translated and these form transfer RNA and ribosomal RNA. The combination of genes expressed in a cell determines the proteins produced, which determines the cells function, for example - as structural components of tissues.

Haemophilia
Haemophilia is a genetic disease caused by a mutation in the gene that codes for clotting factor VIII, Haemophilia A, or clotting factor IX, Haemophilia B. This leads to an inability to clot blood properly, resulting in excessive bleeding and spontaneous bleeding in muscles and joints.

HIV (Human Immunodeficiency Virus)
HIV is a virus that causes immune system failure and leads to AIDS - Acquired Immunodeficiency Syndrome.

Huntingdon's Disease
Huntingdon's Disease is a disease characterised by involuntary twitching movements of the face, and jerking, flicking or fidgety movements of the limbs and body. These move from one area of the body to another. Huntingdon's disease also features alternating periods of aggression, anger, excitement and depression, and progressive loss of memory and personality.

IVF (In Vitro Fertilisation)
IVF is the process in which egg and sperm are fertilised in a petri dish and then inserted back into the uterus.

Muscular dystrophy
Muscular dystrophy is a muscle disorders caused by a gene defect in which slow, progressive muscle wasting occurs, leading to increasing weakness and disability.

Nucleotide
A nucleotide is a subunit of DNA or RNA consisting of a base (adenine, guanine, thymine or cytosine in DNA; adenine, guanine, uracil or cytosine in RNA), a phosphate molecule, and a sugar molecule. The nucleotide units are joined together via their sugar-phosphate groups to make up a DNA or RNA molecule and its sequence is described as the sequence of its bases, e.g. AAAAGTTCGTCTAGGTC. The two strands of a DNA molecule are held together as a double helix by weak bonds between base pairs: adenine and thymine, or guanine and cytosine.

Ribonucleic acid (RNA)
RNA acts as a messenger molecule in protein synthesis. Genes encoded in DNA are copied into RNA which travels from the cell nucleus to be decoded by the protein-making factories in the cytoplasm. Like DNA, RNA consists of a sequence of nucleotide subunits, but differs slightly in its chemical make up: the sugar is ribose not deoxyribose and, instead of thymine, RNA has uracil bases that pair with adenine. RNA is not a double helix shape but is folded up.

There are several types of RNA - including messenger RNA, transfer RNA, ribosomal RNA - each serving a different function.

Messenger RNA (mRNA)
Messenger RNA is a molecule of RNA, whose sequence of bases is complimentary to the coding sequence of a gene. It serves as a template for protein synthesis and carries the genetic information out of the nucleus to the protein-making factories in the cytoplasm, where transfer RNA decodes the information carried by mRNA to enable ribosomal RNA to make protein.

Nucleus
The nucleus is the centre of core of a cell where all the genetic information is stored.

Leukaemia
Leukaemia is a disease of the bone marrow where there is uncontrolled division of white blood cells, resulting in anaemia, impaired blood clotting and enlargement of lymph nodes, liver and spleen.

Protein
Proteins are large, complex molecules, composed of one or more chains of subunits called amino acids. Twenty different amino acids are usually found in proteins. Within a gene, each specific sequence of three DNA bases (known as codons) direct the cell's protein synthesising machinery to add specific amino acids. The genetic code is thus a series of codons that determine which amino acids are required to make up specific proteins. Each protein has unique functions and are required for the structure, function and regulation of the body's cells, tissues, and organs, for example - hormones, enzymes, and antibodies.

Mutations
Mutations occur when mistakes happen during gene replication. A base is missed, or whole segments of DNA are sometimes reversed, deleted or inserted. Many mutations have no effect but, if it occurs in the DNA sequence encoding or controlling a gene, the properties of the protein produced can be changed. A mutation could cause a disorder or the inherited susceptibility to a disorder.

Genetic Code
The genetic code is the sequence of nucleotides, coded as three DNA bases (codons), along the mRNA, which determines the sequence of amino acids in protein synthesis. The DNA sequence of a gene can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence.

Tay-Sachs Disease
A genetic disease that effects young children, in which a missing protein leads to mental retardation, convulsions, blindness and early death.

Genetic Testing
The process of carrying out a test to detect the presence of, absence of, or change in a particular gene or chromosome.

Virus
A sub-microscopic infective agent made up of a core of RNA or DNA, surrounded by a protein coat. A virus is not able to replicate without a host cell and is typically not considered a living organism.