DNA Sequence

A DNA sequence is how the sequence or order of nucleotide bases in a piece of DNA is determined. DNA (deoxyribonucleic acid) contains all the information needed to build and maintain an organism – whether it is a human, a dog or a bacteria cell. DNA molecules are composed of four nucleotides, and these nucleotides are linked together much like the other words in a sentence.

These four nucleotides are; Adenine (As), Guanine (Gs), Cytosine (Cs), and Thymine (Ts) and they contain the instructions for building the proteins and other molecules that the cell needs to carry out its daily work.

Types of DNA Sequencing technologies

Sequencing an entire genome (all of an organism’s DNA) has remained a hard task for a long time since it requires breaking the DNA of the genome into many smaller pieces, sequencing the pieces and assembling the sequences into a single long piece.\

But recently, a breakthrough was made and now we have genome sequencing much faster and less expensive using these methods:

  1. Sanger sequencing - In this method, the target DNA is copied multiple times which results in fragments of different lengths. Through chain termination, “chain terminator” nucleotides mark the ends of the fragments and allow the sequence to be determined.

  2. Next-generation sequencing (NGS) - While a number of improvements have been made to Sanger sequencing over the years, new high-throughput techniques have also arisen, termed next-generation sequencing (NGS) technologies. These techniques have increased the speed and reduced the cost of DNA sequencing.

  3. Capillary electrophoresis and fragment analysis - Capillary electrophoresis (CE) instruments are able to perform both sanger sequencing and fragment analysis. This technique is used to determine the specific base sequence of a particular gene segment, it can also provide sizing, relative quantitation and genotyping information for fluorescently labelled DNA fragments.

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