Reading frame

The genetic code consists of a sequence of letters which are read in groups of three. There are three possible ways of reading the sequence depending on the starting point. If the code reads AGCAGCAGC, for example, the three reading frames are AGC AGC, GCA GCA and CAG CAG.

Recessive

A form of inheritance in which a faulty copy of a gene is inherited from each parent (in order to develop the disorder an individual has to have two copies of the faulty gene). Includes X-linked recessive and autosomal recessive modes of inheritance.


Revertant fibres

Occasional fibres seen in muscle biopsies, which contain forms of dystrophin, even though the genetic mutation should prevent the production of this protein. The fibres are generally too rare to be useful.

RNA

Ribonucleic acid, a substance very similar to DNA. When a gene is ‘switched on’, RNA copies of the gene’s code are made. These are called messenger RNA (mRNA) and move outside the nucleus where they direct the manufacture of proteins. Some forms of RNA carry amino acids, which can be added to the growing protein chain – these are called transfer RNA (tRNA).