Unlocking the Secret of Human Genome

Your DNA sequence, essentially your blueprint of life, encodes the necessary information for survival and reproduction. Thus, determining the sequence is therefore useful for the studies of life itself.

DNA is made up of four different types of nucleotides which differ from each other in their nitrogenous bases. The four different bases are Adenine (A), Thymine (T), Guanine (G) and Cytosine (C). In the double helix of a DNA molecule, A will base-pairs with T, while G will base-pairs with C.

The process of determining the order of nucleotides on a strand of your DNA is termed DNA sequencing.

The most common method of sequencing, developed by Frederick Sanger, is called the “chain termination method”. Sequencing is achieved by mixing four deoxynucleotides (with A, T, C, or G bases) along with a low concentration of fluorescently labeled chain-terminating di-deoxynucleotides (with A, T, C, or bases; each with a fluorescence molecule of different colour) with the DNA of interest. The deoxynucleotides will base-pair with and chain polymerize on the DNA of interest.

The polymerization reaction is terminated only when a complementary di-deoxynucleotide is encountered at random, thus generating newly synthesized DNA fragments of varying length.

These fragments are later separated according to their sizes by capillary electrophoresis. Since each of the dideoxynucleotide chain-terminators fluoresces at a different wavelength, DNA sequence can be determined by reading the fluorescence signal according to the order of fragment size.