The human genome contains 3.2 billion chemical nucleotide base pairs   (A, C, T, and G).

·   The average gene consists of 3,000 base pairs, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million base pairs.

 

Functions are unknown for more than 50% of discovered genes.

  The human genome sequence is almost exactly the same (99.9%) in all people.

·   About 2% of the genome encodes instructions for the synthesis of proteins.

·   Repeat sequences that do not code for proteins make up at least 50% of the human genome.

·   Repeat sequences are thought to have no direct functions, but they shed light on chromosome structure and dynamics. Over time, these repeats reshape the genome by rearranging it, thereby creating entirely new genes or modifying and reshuffling existing genes.

·   The human genome has a much greater portion (50%) of repeat sequences than the mustard weed (11 %), the worm (7%), and the fly (3%).

·   Over 40°/o of predicted human proteins share similarity with fruit-fly or worm proteins.

·   chromosome 1 (the largest human chromosome) has the most genes (3,168), and Y chromosome has the fewest (344).

·   Particular gene sequences have been associated with numerous diseases and disorders, including breast cancer, muscle disease, deafness, and blindness.