GENOME SEQUENCING PROJECTS

To understand the functional and structural aspects of a gene, one needs to know the sequence of a gene. Sequencing can be mainly by using two methodologies:

a) Directed Sequencing of BAC Contigs - BAC (Bacterial Artificial Chromosome) vectors are used to make genomic libraries in which the insert size is 80-100 kb. After screening and locating the common restriction fragments, the BAC clones are then mapped to find the overlapping arrays of contiguous clones called contigs. The large DNA fragments are then broken into small pieces to complete the sequencing of mapped contigs. Hence,
using this directed strategy, DNA pieces from adjacent stretches of a chromosome are sequenced.

b) Random Shotgun Sequencing - In this method, the genome is randomly broken up into sizes of 2-10 kb range and then inserted into a vector (plasmids). These are then sequenced with the help of overlapping or common sequences. A computer program identifies the overlapping sequences and joins them into one continuous stretch.

THE ADVANTAGES OF SEQUENCING THE GENOME

a) It provides a basis for the discovery of all genes and thus one can construct an inventory of genes.
b) The sequence shows the relationships between the genes which helps in future experimentation.
c) The sequencing provides an index to draw and organize all genetic information about the organism.
d) For times to come, the whole genome sequence becomes an archive for the future which contains all the genetic information required to make an organism.

After the sequencing of the genes, we can investigate the functional properties such as the rate of transcription, the level of expression under different environmental conditions of genes. Two techniques have been used to understand the working of the genes