Chemistry, medicine and genetic analysis

Genetic analysis, the detection of genomic nucleic acid sequences (see Box), is an important tool in modern science, having many applications. The detection of species-specific genes (short fragments of deoxyribonucleic acid, DNA) in host tissues can show the presence of pathogens or viral genes embedded in the host's genome. Infectious diseases such as HIV, Chlamydia trachomatis and hepatitis C can be diagnosed, as can bioterrorism agents in sterile body fluids. 

In addition to the detection of DNA, RNA (ribonucleic acid) sequences can also be targeted. In the synthesis of a protein, a gene is copied as a single-stranded molecule (RNA). This messenger molecule, mRNA, moves to the part of the cell where proteins are synthesised (the ribosome) and acts as a template for the new protein. Detection of mRNAs can show which genes are being used, and at what levels. This can provide information about key processes that are occurring in an organism at a specific time. For example, increased expression of oestrogen receptor α is found in human breast carcinomas. 

Mutations or changes to an individual's genome can lead to genetic diseases. Large genomic duplications and deletions (of the kilobase order) are the recognised cause of several inherited diseases, including β-thalassaemia (a serious form of anaemia), Duchenne and Becker muscular dystrophies (marked by weakness and wasting of selected muscles), and familial breast cancer. At the other end of the scale, slight mutations in an individual's genome (a change in just one base pair, for example) can lead to Huntingdon's disease, cystic fibrosis, and sickle-cell anaemia.