In the past, efforts to understand genes and their expression have been confounded by the immense size and complexity of human deoxyribonucleic acid (DNA).
Biotechnology and Human Disease
OVERVIEW
In the past, efforts to
understand genes and their expression have been confounded by the immense size
and complexity of human deoxyribonucleic acid (DNA). The human genome contains
approximately three billion (109) base pairs (bp) that encode 20,000 to 25,000
protein-coding genes located on 23 chromosomes in the haploid genome. It is now
possible to determine the nucleotide sequence of long stretches of DNA, and the
entire human genome has been sequenced. This effort (called the Human Genome
Project and completed in 2003) was made possible by several techniques that
have already contributed to our understanding of many genetic diseases (Figure
33.1). These include, first, the discovery of restriction endonucleases that
permit the cleavage of huge DNA molecules into defined fragments. Second, the
development of cloning techniques that provide a mechanism for amplification of
specific nucleotide sequences. Finally, the ability to synthesize specific
probes, which has allowed the identification and manipulation of nucleotide
sequences of interest. These and other experimental approaches have permitted
the identification of both normal and mutant nucleotide sequences in DNA. This
knowledge has led to the development of methods for the diagnosis of genetic
diseases and some successes in the treatment of patients by gene therapy.
[Note: The genomes of several viruses, prokaryotes, and nonhuman eukaryotes
have also been sequenced.]
Figure 33.1 Three techniques
that facilitate analysis of human DNA. dsDNA = double-stranded DNA.
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