 Hi everyone, welcome to basic science series. An illegal specific oligonucleotide or ASO is a short piece of synthetic DNA complementary to the sequence of a variable target DNA. It acts as a probe for the presence of target in a southern blot assay or more commonly in a simpler dot blot assay. It is a common tool used in genetic testing, forensics and molecular biology research. An ASO is typically an oligonucleotide of 15 to 21 nucleotide bases in length. It is designed and used in a way that makes it specific for only one version or allele of the DNA being tested. The length of the ASO, which strand it is chosen from and the conditions by which it is bound to or washed from the target DNA plays a very important role in its specificity. These probes can usually be designed to detect a difference of as little as one base in the target DNA sequence, a basic ability in the assay of single nucleotide polymorphism important in genotype analysis and the human genome project. To be detected after it is bound to the target, the ASO must be labeled with a radioactive enzymatic or a fluorescent tag. The human disease sickle cell anemia is caused by a genetic mutation in the codon for the sixth amino acid of the blood protein beta hemoglobin. The normal DNA sequence GAG codes for the amino acid glutamate, while the mutation changes the middle adenine to thiamine leading to the sequence GTG. This altered sequence substitutes a valine into the final protein, distorting its structure. To test for the presence of mutation in a DNA sample, an ASO probe would be synthesized to be complementary to the altered sequence. As a control another ASO would be synthesized for the normal sequence. Each ASO is fully complementary to its target sequence and will bind strongly. Using this technology we can detect the presence of the gene defect in any sample. I hope now you have all the basic information for ASO which is allele specific oligonucleotide. If you like the video please subscribe the basic science series YouTube channel for new videos.