A mutation is any change in the DNA sequence. Mutations can lead to genetic disorders or disease. Most mutations are recognised because the phenotype, that is the characteristics displayed by an organism, have changed. There are many different types of mutation. They can occur on a macroscopic level in the form of chromosomal mutations or they may be the result of a single base pair change in the DNA sequence. Mutations can occur within a gene preventing the synthesis of the correct protein, they may occur in gene promoter regions or in DNA regulatory regions changing the expression levels of the protein, or near the splice sites in introns causing disruption to the splicing process and production of an incorrect protein.
Mutations are rare events occurring at a rate of 1 in every 50 million bases added to the nucleotide chain. Most of the changes that happen are quickly repaired by our very efficient and accurate DNA repair system. However, this repair mechanism is not foolproof. Failure to repair all mutations has led to the introduction of some mutations that have made organisms fitter and better able to adapt to their environments. However, many mutations have detrimental effects for an organism and it is these mutations that are the basis of many human genetic disorders and disease.
A healthy body depends on the interaction between thousands of proteins, acting together in the correct amounts and in the correct places. Proteins are what perform all of the body's essential functions - fighting infections, growth and repair, detoxifying toxins, metabolising food and much more. Mutations in our genes can result in the production of a completely malformed protein that is unable to carry out its functional role or they may change the amount of a protein being produced.
The outcome of a particular mutation depends both on how it alters a proteins function and also on how vital that protein is to our survival. Failure to produce proteins in the correct amounts or at all can disrupt essential metabolic, regulatory or signalling pathways resulting in the development of disease.
Gene mutations can either be inherited from a parent or acquired. A hereditary or germline mutation is present in every cell of the body. They are called germline mutations because they are present in the germ cells or reproductive cells and in this way they can be passed from one generation to the next. These mutations are copied every time a body cell divides. Acquired mutations or somatic mutations are changes that occur during a persons lifetime. Somatic cells include all body cells except for the reproductive cells.
These somatic mutations are changes in the genomic sequence of individual cells and they are only passed to cells that are directly derived from the original cell. These mutations are often a result of the failure of the cells DNA repair mechanism to correct a mistake that has occurred during cell division. The body's repair machinery is highly accurate most of the time (uncorrected errors occur at the rate of about 1 in every 50 million nucleotides added to the chain) becoming a little less efficient with age. Somatic mutations can also be the result of environmental stresses such as cigarette smoke, over exposure to the sun, radiation, car fumes, pesticides and many more.
