question_answer 83)

    Give an account of the methods used in sequencing the human genome.

Answer:

                    Sequencing of human genome has made it possible to understand the link between various genes and their functions. If there are any gene defects that express as disorders or that increase the susceptibility of an individual to a disease then specific gene therapies can be worked out Methodoiogies of human genome sequencing The methods involve two major approaches (i) Expressed Sequence Tags (ESTs) This method focusses on identifying all the genes that are expressed as RNA. (ii) Sequence annotationIt is an approach of simply sequencing the whole set of genome that contains all the coding and non-coding sequences, and later assigning different regions in the sequence with functions. For sequencing, first the total DNA from cell is i.e., solated and broken down in relatively small sizes as fragments. There DNA fragments are cloned in suitable host using suitable vectors. When bacteria isused as vector, they are called Bacterial Artificial Chromosomes (BAG) and when yeast isused as vector, they are called Yeast Artificial Chromosomes (YACs). Frederick Sanger developed a principleaccording to which the fragments of DNA aresequenced by automated DNA sequences. On the basis of overlapping regions on DNA fragments, these sequences are arranged;accordingly. For alignment of these sequences, specialized computer-based programmeswere developed. Finally, the genetic and physical maps of the genome were constructed by collectinginformation about certain repetitive DNA sequences and DNA polymorphism, based onendonuclease recognition sites.