Monday 19 October 2015

Principle of DNA Sequencing



The DNA (deoxyribonucleic acid) sequencing is a technique used to determine the nucleotide sequence of DNA. The nucleotide sequence is the most fundamental level of knowledge of a gene or genome. It is the blueprint that contains the instructions for building an organism, and no understanding of genetic function or evolution could be complete without obtaining this information.
Finding a single gene amid the vast stretches of DNA that make up the human genome - three billion base-pairs' worth - requires a set of powerful tools. The Human Genome Project (HGP) was devoted to developing new and better tools to make gene hunts faster, cheaper and practical for almost any scientist to accomplish. These tools include genetic maps, physical maps and DNA sequence - which is a detailed description of the order of the chemical building blocks, or bases, in a given stretch of DNA.

Scientists need to know the sequence of bases because it tells them the kind of genetic information that is carried in a particular segment of DNA. For example, they can use sequence information to determine which stretches of DNA contain genes, as well as to analyze those genes for changes in sequence, called mutations, that may cause disease.

How is DNA Sequencing Performed?
DNA sequencing involves the process of figuring out the precise order of the four bases found in one piece of DNA. What this means is that the DNA is really just a template that is used to create a series of fragments. The fragments differ in length by one base and they are separated by size before the bases are identified, which then effectively recreates the original DNA sequence.

Each person has twenty-three pairs of chromosomes - one copy of the human genome. Because technology has limitations, we are limited in how many bases can be read at one time. Therefore, we can't just read each base from one end of a chromosome to the other. To make it feasible, the chromosome is cut down into smaller fragments.

Why Perform DNA Sequencing?
DNA sequencing is important to apply to the human genome. It allows scientists to sequence genes and genomes. Since there is a limit to how many bases can be sequenced in one experiment, larger DNA molecules - as mentioned - have to be 'broken' into smaller fragments before they can be sequenced and reassembled. To ensure that the sequencing is accurate researchers performs the sequencing several times.

Clearly, finding just one single gene amongst the seemingly endless strands of DNA that constitute the human genome needs some very powerful equipment! With continued research, it is likely that better tools will be developed to make DNA sequencing much more rapid as well as cheaper and more practical for researchers to complete. In doing so, we will have a better understanding of the base sequences that can tell us important genetic information in one specific segment of DNA. Once genes are identified and analyzed from sequence information, scientists can look for mutations that cause disease, thereby providing valuable medical information.


AnilaRani, professor in biotechnology has conducted various seminars to demonstrate the principles involved in DNA sequencing. DNAsequencing by radioactive labeling is thankfully no longer necessary due to the advent of dye-terminator chemistry, whereby a single strand of DNA can be labeled with a fluorescent dye corresponding to the base at the 3'end of the fragment.

1 comment:

  1. Mrs. Anila Rani is an extremely talented and knowledgeable professor. I have been her student and as per my experience I can say that she is one of the best teachers I have ever known. I would always remember her because she has been a very influential person in my life and she always inspired me to work harder..

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