Glossary

A,G,C,T: These letters stand for the 4 chemical components of DNA; adenine, guanine, cytosine and thymine.

Allele: One of two or more alternate forms of a gene.

Amino acid: These are 20 different small molecules that can join together to form proteins.  They are often referred to as the building blocks of proteins and their sequence in a protein is determined by information in the genetic code.  Enzymes can break down proteins into their amino acid components during digestion.

Antibody: A protein that circulates in the blood and other body fluids. An antibody binds to a specific antigen and marks it for destruction by making it easier for  an immune system cell (phagocyte) to ingest the antigen.

Antigen: A substance that is recognized by the immune system - normally a foreign invader such as a virus of bacterium - and elicits an immune response.

Autosome: Chromosome that is the same in males and females; nonsex chromosome.

Autosomal dominant/recessive: A pattern of Mendelian inheritance whereby an affected individual possesses one copy of a mutant allele and one normal allele. (In contrast, recessive diseases require that the individual have two copies of the mutant allele.) Individuals with autosomal dominant diseases have a 50-50 chance of passing the mutant allele and hence the disorder onto their children.

Chromosome: One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.

Chromosome mutation: Difference from the wild type in the number or structure of one or more chromosomes; often affects many genes and has very obvious effect on an individual's characteristics.

Consanquinity: Mating between related individuals.

DNA: The chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.

DNA sequencing: Process of determining the sequence of bases along a DNA molecule.

Deletion: Mutation in which one or more nucleotides are deleted from a DNA sequence.

Enzyme: Special chemicals in the digestive system that break down large molecules into smaller ones

Gene: A segment of DNA, found in the nucleus of cells on chromosomes, that contains instructions to make a protein.  Genes determine characteristics in an individual such as hair and eye colour which can be inherited.

Gene mutation: A difference or change in a single gene or locus.

Genotype: The set of genes possessed by an individual.

Homozygous: Possessing two identical forms of a particular gene, one inherited from each parent.

Heterozygous: Possessing two different forms of a particular gene, one inherited from each parent.

Karyotype: A picture of an organism’s complete set of condensed (metaphase) chromosomes.

Locus: Position on a chromosome where a specific gene is located.

Mutation: An inherited change in genetic information.

Pedigree: A pictorial representation of a family history outlining the inheritance of one or more traits or diseases.

Protein: A large complex molecule made up of one or more chains of amino acids. Proteins perform a wide variety of activities in the cell.

Penetrance: Percentage of persons with a particular genotype that express the phenotype expected of that genotype.

Trisomy: Presence of an additional copy in a chromosome.

Wild type: The allele or trait that is most commonly found in natural (wild) populations.

X-linked-characteristic(s): Determined by a gene or genes on the x chromosome.

Y-linked-characteristic(s): Determined by a gene or genes on the y chromosome.