Chapter 12: Genomics, Proteomics, and Transgenics
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
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