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.