Comparative genomics

With genomic data through DNA sequencing becoming more simply available it is becoming increasingly relevant to consider the whole of a microorganism rather than its individual genes. In this way subtle differences can be examined for example what makes Bacillus anthracis the causative agent of anthrax compared to the genetically very similar Bacillus cereus. The arrangement of genes relative to one another their presence or absence, the  sequence of the  genes and  intergenic regions are all used not  only to compare species  of Bacteria but  also  to examine more distant relationships for example among higher animals and  microorganisms. The size of higher organisms’ genomes the human genome is 3200 million bp Mbp has made widespread whole genome sequencing a task performed through a few consortia of public and private laboratories worldwide. However, the relatively small size of Bacterial and Archaeal genomes 3–8 Mbp has led to the release of new complete genome sequences on an almost weekly basis.  The way in which DNA sequences are assembled and obtained into genome-sized pieces is beyond the scope of this text but a primary consideration in approaching genomics is how the microorganism’s genome is arranged.