Glossary of Genetic Terminology
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A condition in which the amount of iron in the body is much higher than usual; the iron builds up over time in various organs such as the liver, heart and brain. The condition can be associated with another medical problem or it may be inherited (hereditary haemochromatosis). If untreated, the build-up of iron may lead to conditions such as arthritis, cirrhosis of the liver, cardiomyopathy and diabetes (see Genetics Fact Sheet 36).
A genetic condition that causes people to continue bleeding for a long time unless treated. Bleeding is common into joints such as knees, ankles and elbows. Sometimes bleeding into muscles or internal organs may occur. The blood is unable to clot properly due to missing or abnormal proteins that facilitate clotting (see Genetics Fact Sheet 40).
HAPLOID NUMBER:
This is the number of chromosomes in the sex cells (sperm or egg). There is one copy of each chromosome. In humans, the haploid number is 23.
A set of closely linked alleles on a chromosome that is normally inherited as a block.
Please see 'Deafness'.
HEREDITARY:
The transfer of a gene from parent to child. In mothers, the gene is transferred via the DNA in the egg and in fathers the gene is transferred via the DNA of the sperm.
A condition most likely due to the interaction of changes in a number of different genes that leads to a susceptibility to the condition, triggered by environmental factors that may include diet, obesity and stress (see Genetics Fact Sheet 56).
The passing of genetic characteristics form parent to child.
The degree to which a characteristic is determined by genetics or genes.
An individual who has two different alleles at a particular gene locus, one on each chromosome of a pair; one allele is usually normal and the other abnormal. Such an individual may also be referred to as a carrier.
HOMOZYGOTE:
Refers to an individual in whom the two alleles or gene copies contain identical information. An individual can be
homozygous for the correct copies of the gene or can be homozygous for the mutated copies of the gene.
HORMONE:
A chemical product of the body which has a specific regulatory effect upon the cells.
The international scientific effort that began in the 1980s to 'read' the order of bases (sequence) as they appear in the DNA of human chromosomes. The objective is to create a directory of the genes that can be used to answer questions such as what specific genes do and how they work (see Genetics Fact Sheet 24).
A neurodegenerative genetic condition where the symptoms of involuntary movements and changes in personality usually appear slowly between the ages of 30 and 50 (see Genetics Fact Sheet 44).