Most of the non-transcribed DNA consist of promotors and regions that regulate transcription initiation.

b)  Since gene products in mammals and  bacteria are similair in size, the amount of DNA in the exons of a typical mammalian gene must also be about 1000 bp.  The total amount of DNA in the exons is therefore:

5 x 10⁴ genes x 1 kb/gene= 5 x 10⁴ kb

This DNA represents

(5 x 10⁴ kb/ 3 x 10⁶ kb) x 100%= 1.7 % of the mammalian genome.

The remaining 98.3% of the DNA consists of introns and other sequences.