Glossary

Alleles - Alternative forms of a gene at the same locus.

Autoradiography - Detection of radioactively labelled molecules with X-ray film.

Autosome - Any chromosome other than the sex (X or Y) chromosomes.

Carrier - A healthy person who is a heterozygote for a recessive trait. Also refers to a person with a balanced chromosomal translocation.

Clone - All the cells derived from a single cell by repeated cell division and having the same genetic constitution.

Coding sequence - Sequence of bases in DNA which specifies the structure of a protein.

Consanguineous - Where two people are related by blood (i.e. share a least one common ancestor).

Consultand - A person requesting genetic counselling.

Cytogenetics - The branch of genetics concerned with the physical structure and appearance of chromosomes.

Dominant - A trait expressed in a heterozygote.

Dysmorphic - An alteration in the normal form or appearance.

Empiric risk - Recurrence risk based on experience rather than calculation.

Expressivity - Variation in the severity of a genetic trait.

Flanking markers - Markers on either side of a disease locus.

Gamete - A germ cell (sperm or ovum).

Gene - The unit of inheritance: a part of the DNA molecule which directs synthesis of a specific polypeptide.

Gene tracking - Following a gene through a family by observing the inheritance of a marker which is being inherited alongside the gene.

Genetic counselling - Process by which information on genetic disorders is given to a family.

Genotype - The genetic constitution of an individual.

Gonadal mosaicism - Presence of a mutation in germline but not somatic cells, which results in transmission of a genetic disorder by a healthy person.

Heterozygote - An individual with one normal and one mutant allele at a given locus on a pair of homologous chromosome.

Homologous - Matched (usually of a pair of chromosomes).

Homozygote - Person having two identical alleles at a particular locus on homologous chromosomes.

Hybridisation - Process by which single strands of DNA (or RNA) with homologous sequences bind together.

Karyotype - The classified chromosome complement of an individual or cell.

Locus- The precise location of a gene on a chromosome.

Marker - Biochemical or DNA polymorphism occurring close to a gene and used in gene tracking.

Mendelian disorder - Inherited disorder due to a defect in a single gene.

Mitochondria - organelles in a cell's cytoplasm chiefly responsible for "energy production".

Monosomic - Having only one of the pair of genes, DNA segments or whole chromosomes from a pair of homologous chromosomes.

Mosaic - Individual derived from a single fertilised egg, but where an error in cell division or a new mutation leads to cells of two or more different genotypes.

Multifactorial - Inheritance due to multiple genes at different loci which summate and interact with environmental factors.

Mutation - An alteration in the structure of DNA.

Penetrance - Probability that a disease genotype will result in an abnormal phenotype.

Phenotype - The observable characteristics of an individual.

Polymorphism - Genetic characteristic with more than one common form in a population.

Proband - The individual who draws medical attention to a family.

Probe - A DNA (or RNA) fragment which has been labelled (usually with radioactivity) and used in a hybridisation assay to identify related DNA (or RNA) sequences.

Recessive - A trait expressed only in homozygotes.

Sex-linked - Inheritance of a gene carried on a sex chromosome.

Single gene disorder - Disease whose inheritance is controlled by one pair of genes (one on each homologous chromosome).

Somatic cell - Any cell in the body except the gametes.

Trait - Any gene-determined characteristic.

Translocation - The transfer of chromosomal material between chromosomes.

Trisomy - Three copies of a given chromosome per cell.

This page was last modified on Fri Feb 12 2010