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t m c ยป p u l s e | s e p t e m b e r 2 0 1 5 21 WHAT IS WHOLE EXOME SEQUENCING? An efficient method of analyzing a patient's DNA to discover the genetic cause of diseases or disabilities, whole exome sequencing only examines the protein-coding region of the human genome that contains functionally important sequences of DNA that direct the production of proteins essential for the body to function properly. It is known that most of the errors that occur in DNA sequences that lead to genetic disorders are located within this region. By mapping this region and comparing it to a normal reference sequence, variations in an individual's DNA can be identified and then related back to an individual's medical condition. WHAT IS DNA SEQUENCING? DNA sequencing is the process of determining the exact order of nucleotides within a molecule of DNA. This provides data about the kind of information carried in a particular segment of DNA, such as whether or not it contains genes or if there are any mutations in the sequence. The ability to map DNA is becoming increasingly useful in medicine as well as other scientific fields, such as evolutionary biology and forensics. WHAT IS DNA? Deoxyribonucleic acid, or DNA, is a molecule that carries the genetic information responsible for the development, function and reproduction of living organisms. DNA is comprised of chemical building blocks called nucleotides, which are made up of phosphate, sugar and one of four types of nitrogen bases. The nucleotides link into chains and, through nitrogen base pairing, coil around other chains of nucleotides to create a double helix. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases determines what biological instructions are coded within the strand of DNA. DNA SEQUENCING G E N E T I C VA R I AT I O N S & M U TAT I O N S These changes could be caused by a single substitution, deletion or addition of one base pair in DNA. that may contribute to the is used to search for DEVELOPMENT OR PROGRESSION OF A DISEASE. WHAT IS A MUTATION? A mutation is a change in the DNA sequence, either due to a mistake during DNA replication or exposure to environmental factors such as radiation or cigarette smoke. It can be caused by the alteration of a single nucleotide or the deletion, insertion or rearrangement of larger sections of genes or chromosomes. Mutations can be acquired during a person's life or inherited from a parent. Although some mutations are beneficial in that they provide genetic variation in a population, many are harmful; cancer, for example, is caused by mutations in cell-growth controlling genes. WHAT IS CLINICAL GENOMICS AND WHY IS IT IMPORTANT? Clinical genomics can be defined as the medical application of studying the complete genetic material of a living organism. This branch of science has the potential to revolutionize health care, leading to better understanding of the biological systems that govern the human body and the development of new diagnostics and treatments.