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● Two methods − identifying ESTs (Expressed sequence Tags) and
sequence annotation

● ESTs − As the name suggests, this refers to the part of DNA that is
expressed, i.e. transcribed, as mRNA and translated into proteins

thereafter. It basically focuses on sequencing the part denoting a
gene.

● Annotation − In this approach, entire genome (coding + non­coding)
is sequenced and later on function is assigned to each region in the
genome.

Genome Sequencing

● DNA from the cells is isolated and is randomly broken into fragments
of smaller sizes.

● These fragments are cloned into suitable host using vectors.
● Cloned fragments amplify in the host. Amplification facilitates an easy
sequencing.

● Common vectors used − BAC (Bacterial artificial chromosomes) and
YAC (Yeast artificial chromosomes)

● Common hosts − Bacteria and yeasts
● Automated sequencers are used to sequence these smaller fragments

(Sanger sequencing).
● The sequences so obtained are arranged based on overlapping regions

within them (alignment).
● Alignment of the sequences is also done automatically by computer
programs.

● Then these sequences are annotated and assigned to each
chromosome.

Preparation of Genetic and physical maps on Genome

● 2 methods are used − restriction polymorphism and microsatellites

● Restriction polymorphism − Specialized enzymes called restriction
endonucleases are used to cut the genome at specialized sites called

restriction endonuclease recognition site and maps are prepared based
on it.