Chapter12_SSM - 65781_CH12_240_258.qxd 8/1/08 1:15 PM Page...

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Chapter 12: Genomics, Proteomics, and Transgenics Chapter Summary Recombinant DNA technology makes it possible to modify the genotype of an organism in a directed, predetermined way by enabling different DNA molecules to be joined into novel genetic units, altered as desired, and reintroduced into the germ line. Restriction enzymes play a key role in the technique, because they can cleave DNA molecules within particular base sequences. Many restriction enzymes generate DNA fragments with complementary single-stranded ends, which can anneal and be ligated together with similar fragments from other DNA molecules. The carrier DNA molecule used to propagate a desired DNA frag- ment is called a vector. The most common vectors are plasmids, phages, viruses, and bacterial artificial chromosomes. Transformation is an essential step in the propagation of recombinant molecules because it enables the recombinant DNA molecules to enter host cells, such as those of bacteria, yeast, or mammals. If the recombinant molecule has its own replication system or can use the host replication system, then it can replicate. Plasmid vectors become permanently established in the host cell; phage can multiply and produce a stable population of phage carrying source DNA; and retroviruses can be used to establish a gene in an animal cell. Complete DNA sequences have been determined for numerous mitochondria and chloroplasts, as well as for the genomes of many bacteria, archaeans, and eukaryotes including the human genome. Genome anno- tation deals with identifying the functional elements in genomic sequences. It makes use of computer analysis as well as such experimental information as expressed sequence tags (ESTs) and comparative genomics. Beyond analysis of the DNA sequences themselves, and comparisons among organisms, genomics has spawned the field of functional genomics to describe and understand the genome-wide patterns of gene expression in cells under different conditions, including normal development and disease. Proteomics features large-scale studies of proteins, for example, two-hybrid analysis to detect protein-protein interactions. Recombinant DNA can also be used to transform the germ line of animals or to genetically engineer plants. These techniques form the basis of reverse genetics, in which genes are deliberately mutated in specified 240
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241 ways and introduced back into the organism to determine the effects on phenotype. Reverse genetics is routine in genetic analysis in bacteria, yeast, nematodes, Drosophila , the mouse, and other organisms. In Drosophila , transformation employs a system of two vectors based on the transposable P element. One vector contains sequences that produce the P transposase; the other contains the DNA of interest between the inverted repeats of P and other sequences needed for mobilization by transposase and insertion into the genome. Germ-line transformation in the mouse makes use of retrovirus vectors or embryonic stem cells.
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Chapter12_SSM - 65781_CH12_240_258.qxd 8/1/08 1:15 PM Page...

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