62 BIOCHEMISTRY FUNDAMENTALS
together to become part of the sequenced genome. The shotgun approach was
applied to cloned DNA fragments that had already been mapped; that is, the
fragment ’ s location on the genome was already known.
The Human Genome Project delivered a complete human genome sequence
available to scientists in a freely accessible database when it released the fi rst
reference sequence for the human genome in April 2003. The National Insti-
tutes of Health website address for current human genome sequence data and
information is http://www.ncbi.nlm.nih.gov/genome/guide/human/ , and the
National Human Genome Research Institute ’ s researcher resources website
is at http://www.genome.gov/.
The Human Genome Project ’ s goal was to produce high - quality, accurate,
fi nished DNA sequences according to the following standards: (1) The DNA
sequence is 99.99% accurate. (2) The sequence must be assembled; that is, the
smaller lengths of sequenced DNA have been incorporated into much longer
regions refl ecting the original piece of genomic DNA. (3) The task must be
affordable (the project funds technology development to reduce costs as much
as possible). (4) The data must be accessible. To this end, verifi ed DNA sequ-
encing data are deposited in public databases on a daily basis (see the
website http://www.ncbi.nlm.nih.gov/genome/guide/human/ ). In Section 2.3.5 ,
the Sanger and Maxam – Gilbert methods for DNA cleavage followed by gel
electrophoresis for DNA sequencing was described. These so - called fi rst -
generation gel - based sequencing technologies can be used to sequence small
regions of interest in the human genome; however, these methods are too slow
and too expensive for individual chromosomes, let alone a complete genome.
The Human Genome Project, in carrying out their goal of affordability, has
focused on the development of automated sequencing technology that can
accurately sequence 100,000 or more bases per day at a cost of less than $ .50
per base. To achieve this goal, The National Human Genome Research Insti-
tute (NHGRI) has continued to support the development of technologies to
dramatically reduce the cost of DNA sequencing. In 2005, NHGRI awarded
close to $ 25 million (to be spent over several years) to support new and emerg-
ing technologies, including multiple projects that are based on nanotechnology,
specifi cally on nanopores. Modifi ed protein nanopores, for instance, are being
developed. These include (1) genetically engineered α - hemolysin (a bacterial
protein exotoxin capable of hemolysis) pores that would recognize specifi c
bases based on restricted current fl ow through the pore and (2) chemically
modifi ed pores for base recognition using either natural or synthetic nucleo-
bases acting as molecular brakes to slow DNA transit time.
Concurrently with work published by the Human Genome Project, a com-
plete human genome sequence was reported by a consortium of 14 academic,
nonprofi t, and industrial research groups in work coordinated by Celera
Genomics.^21 The following text is excerpted from the abstract of reference 21.
In this work, a 2.91 - billion base - pair (bp) consensus sequence of the euchro-
matic portion (the portion containing genes) of the human genome was
generated by the whole - genome shotgun sequencing method. Two assembly