Gene sequencing I biotechnology I CH#23 I Lec# 7 I F.SC. Biology I Class12

#chapter23 #class12biology #F.sc.biology #chapter23biotecnology
Like Our facebook page.
-----------------------------------
/ bismacademy
------------------------------------
Gene Sequencing.
Definition.
This is the process of studying the sequence of nucleotides in fragment of DNA.
In the late 1970s,
Methods were developed that allowed the nucleotide sequence of any purified DNA
fragments to be determined simply and quickly.
Principle.
The main principle of these methods is :
1. To generate pieces of DNA of different sizes all starting from the same point and
ending at different points.
2. Separation of these different pieces of DNA on agarose gel.
3. Reading of sequence from the gel.
Methods to obtain DNA fragments.
For generation of different sized DNA fragments, two methods are generally used.
Sanger Method.
One is Sanger’s,method in which dideoxyribonucleoside triphosphates arc used to
terminate DNA synthesis at different sites.
Maxam Gilbert Method.
The other method is known as Maxam-Gilbert method in which DNA threads are
chemically cut into pieces of different sizes.
Modern Computerized Methods.
The volume of DNA sequence information is now so large that powerful computers
must be used to store and analyze it. DNA sequence is now completely automated,
Automatic Process.
Robotic devices mix the reagents and then load, run and read the order of the
nucleotide bases from the gel. This is facilitated by using chain terminating
nucleotides that are each labeled with a different colored fluorescent dye; in this
case, all four synthesis reactions can be performed in the same tube, and the
products can be separated in a single lane of a gel. A detector positioned near the
bottom of the gel reads and records the color of fluorescent label on each band as it
passes through a laser beam. A computer then reads and stores this nucleotide
sequence.
Benefits of Automation.
Owing to the automation of DNA sequencing, the genomes of many organisms have
been sequenced.
Examples. These include plant chloroplasts and animal mitochondria, large number
of bacteria, many of the yeasts, a nematode worm. Drosophila, the model plant
Arabidopsis, the mouse and human. Researchers have also deduced the complete DNA
sequence of a variety of human pathogens.