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A simple introduction

Written by the Research Department at the Muscular Dystrophy Campaign and used with their permission.

What are we made of?

The basic structural unit of all living organisms is the cell. Our bodies are made from billions of cells which combine and work together to make every part of our body. Cells have different roles within the body. Cells that perform similar tasks group together to form tissues, such as your kidneys, liver and muscle.

double_helix.jpgAn essential structure within the cell is the nucleus which contains the genetic material that determines all of our characteristics. This genetic information is called DNA or deoxyribonucleic acid. DNA can be likened to coded information which is passed on from generation to generation. It consists of thousands of units called nucleotides consisting of a base (4 types, A, C, G, and T), a sugar and a phosphate. Two strands of nucleotides join to form a ladder like structure which is then twisted into a characteristic double helix.

This coded information is organised on chromosomes. Each chromosome contains the code for hundreds of different genes. Genes are the basic unit of inheritance that determine our make-up. Genes come in pairs, one inherited from each parent. Most genes contain information specific for the production of a protein, eg – peripheral myelin protein 22 (PMP22), too much of which causes CMT Type 1a.

Inheriting genes

Humans have 23 pairs of chromosomes. One set of chromosomes comes from your mother and the other set from your father. The sex cells (the unfertilised egg and sperm) contain only 23 unpaired chromosomes each. Fertilisation of a 23-chromosome egg by a 23-chromosome sperm produces a new 46-chromosome cell, which grows into a new individual. No two people (except identical twins) have the same set of DNA. Errors or mutations in genes can either be inherited or can arise “out of the blue”. Sometimes these errors have no obvious effect and at other times a single letter change, deletion or duplication (as in Type 1a) can have serious consequences.

You may have heard of the words “inheritance pattern”. This refers to the way in which the condition is passed on from generation to generation. There are three main types of inheritance (dominant, recessive and X-linked).



Page updated - 21/05/2013

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