Question

Explain the two major approaches used while sequencing the total DNA from a cell.

Hint:

The approaches are Expressed Sequence Tags (expressed genes only) and Sequence Annotation (whole genome, then function).

Answer 1

Step 1: Why two approaches are needed:
Total DNA of a cell, as in the Human Genome Project, has coding regions (genes) and a very large part of non-coding DNA.
Two major methodologies were used to handle this.

Step 2: Approach 1: Expressed Sequence Tags (ESTs):
Only the genes that are expressed as RNA are identified and sequenced.
This focuses the work on the coding part of the genome.

Step 3: Approach 2: Sequence Annotation:
The whole DNA, both coding and non-coding, is isolated, cut into small fragments and sequenced.
The fragments are arranged in order using overlapping regions. Each sequence is then annotated, that is, given a function and assigned to a gene or a region.

Final Answer:
The two approaches are Expressed Sequence Tags (identifying only the expressed genes) and Sequence Annotation (sequencing the whole genome and then assigning functions).
\[ \boxed{\text{ESTs and Sequence Annotation}} \]