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Genetics of deafness - a glossary

Autosome: One if the chromosomes that is the same in men and women. These are the majority of all our chromosomes – the exception is the pair of sex chromosomes.

Carrier: A person who carries a changed copy of a gene. This may be a recessive gene, in which case the person will not themselves show any of the signs of the condition caused by that changed gene. It may be a dominant gene, in which case the person may develop the condition themselves in time. This chance depends on the particular gene.

Chromosome: One of the 46 strings of genetic material contained in the nucleus (middle) of the cell. A chromosome is made of DNA (With additional proteins helping to package it up) and has many genes lined up along it rather like beads on a string. The chromosomes can be seen with a powerful microscope.

DNA: The chemical that genes and chromosomes are made from. It is made up of chemical building blocks that are rather like single ‘genetic letters’ and therefore make up an individual’s ‘genetic code’. DNA is too small to be seen down a microscope.

Dominant: A changed gene whose effect is ‘dominant’ over the second copy so someone develops a condition even though they also have a working copy.

Gene: A single instruction telling the cell how to make a particular component that it needs to function – usually a protein that might, for example, be important in cell structure or to work as an enzyme to drive a chemical reaction.

Mitochondria: These are little bodies with the cell that generate the energy that the cells need to function. Each mitochondrion carries a short length of DNA with a few genes. This means that, occasionally, a genetic condition is inherited through the mitochondria rather than through the chromosomes.

Penetrance: In this context, this describes how often the effect of a changed gene is seen in the person who carries it. If a gene is ‘fully penetrant’, then everyone carrying it shows some signs.

Recessive: A changed gene whose effect ‘remain hidden’ because the other one of the pair of genes works adequately and can make up or the faulty copy.

Variable: In this context, this describes a genetic condition that varies between people who have it so that they may show different signs or symptoms.

X-linked: A condition caused by a changed gene on the x chromosome.


Information provided by the National Deaf Children's Society.  Reproduced with permission.

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08-Dec-2015 5:43 AM (AEST)