`star` Two major approaches
`star` Methods in detail


● The methods involved in HGP used `color{Violet}"two major approaches"`.

● One approach focused on identifying all the `color{Violet}"genes"` that expressed as `color{Violet}"RNA"` (referred to as `color{Violet}"Expressed Sequence Tags"` (`color{Violet}"ESTs"`).

● The other took the `color{Violet}"blind approach"` of simply sequencing the `color{Violet}"whole set of genome"` that contained all the `color{Violet}"coding and non-coding"` sequence.

● And later it assigned `color{Violet}"different regions in the sequence"` with functions (a term referred to as `color{Violet}"Sequence Annotation"`).


● For sequencing, the `color{Violet}"total DNA"` from a cell is isolated and converted into `color{Violet}"random fragments"` of `color{Violet}"relatively smaller sizes"` (since DNA is a very long polymer, and there are technical limitations in sequencing very long pieces of DNA).

● It is then `color{Violet}"cloned"` in suitable host using `color{Brown}"specialised vectors"`.

● The cloning resulted into `color{Violet}"amplification of each piece"` of DNA fragment so that it subsequently could be sequenced with ease.

● The commonly used hosts were `color{Violet}"bacteria and yeast"`, and the vectors were called as `color{Violet}"BAC"` (`color{Violet}"bacterial artificial chromosomes"`), and `color{Violet}"YAC"` (`color{Violet}"yeast artificial chromosomes"`).

● The fragments were sequenced using `color{Violet}"automated DNA sequencers"` that worked on the principle of a method developed by `color{Violet}"Frederick Sanger"`.

● These sequences were then arranged based on some `color{Violet}"overlapping regions"` present in them.

● This required generation of `color{Violet}"overlapping fragments"` for sequencing.

● `color{Violet}"Alignment"` of these sequences was `color{Violet}"humanly not possible"`.

● Therefore, `color{Violet}"specialized computer"` based `color{Violet}"programs"` were developed.

● These sequences were `color{Violet}"subsequently annotated"` and were assigned to each `color{Violet}"chromosome"`.

● The sequence of `color{Violet}"chromosome 1"` was completed only in `color{Violet}"May 2006"` (this was the `color{Violet}"last of the 24"` human chromosomes – 22 autosomes and X and Y – to be sequenced).

● Another challenging task was assigning the `color{Violet}"genetic and physical maps"` on the genome.

● This was generated using information on `color{Violet}"polymorphism"` of `color{Violet}"restriction endonuclease"` `color{Violet}"recognition sites"`, and some repetitive DNA sequences known as `color{Violet}"microsatellites"`.