||Bacterial artificial chromosomes (BACs) are large segments of
DNA, between 100,000 and 200,000 bases long, cloned from another species
into bacterial DNA. Once the foreign DNA has been cloned into the host
bacteria, many copies of it can be made, and the BACs can then be stored
in order in libraries.
||Bioinformatics is the application of information
technology to analyse and manage large data sets resulting from gene sequencing
or related techniques.
||Complementary-DNA (cDNA, also called ‘copy
DNA’): cDNA is a sequence acquired by copying a messenger RNA (mRNA)
molecule back into DNA. In contrast to the ‘original’ DNA, mRNA codes for
an expressed protein without non-coding DNA sequences (‘introns’). Therefore,
a cDNA probe can also be used to find the specific gene in a complex DNA
sample from another organism with different non-coding sequences.
||Expressed sequence tags (ESTs) are short
sections of cDNA, which are long enough to identify a new cDNA uniquely.
||Functional genomics tries to convert the
molecular information represented by DNA into an understanding of gene
functions and effects: how and why genes behave in certain species and
under specific conditions. To address gene function and expression specifically,
the recovery and identification of mutant and over-expressed phenotypes
can be employed. Functional genomics also entails research on the
protein function (‘proteomics’) or, even more broadly, the whole metabolism
(‘metabolomics’) of an organism.
||Genomics is the study of how genes and genetic information are
organized within the genome, and how this organization determines their
function. This science was given an impetus by the Human Genome Project
(see the article by Lehmann and Lorch), which
stimulated the development of efficient and cheap sequencing techniques.
A number of microbial genomes have already been sequenced, followed closely
by simple eukaryotic genomes like yeast and the nematode Caenorhabditis
||Gene chips (also called ‘DNA chips’) or microarrays. Identified
expressed gene sequences of an organism can, as ESTs or synthesized oligonucleotides,
be placed on a matrix. This matrix can be a solid support like glass. If
a sample containing DNA or RNA is added, those molecules that are complementary
in sequence will hybridize. By making the added molecules fluorescent,
it is possible to detect whether the sample contains DNA or RNA of the
respective genetic sequence initially mounted on the matrix.
||High throughput (HTP) screening makes use of techniques that
allow for a fast and simple test on the presence or absence of a desirable
structure, such as a specific DNA sequence. HTP screening often uses DNA
chips or micro-arrays and automated data processing for the large-scale
screening, for instance to identify new targets for drug development.
||Insertion mutants are mutants of genes
that are obtained by inserting DNA, for instance through mobile DNA sequences,
‘transposons’. Furthermore, in plant research, the capacity of the bacterium
to introduce DNA into the plant genome is employed to induce mutants. In
both cases, mutations lead to lacking or changing gene functions which
are revealed by aberrant phenotypes. Insertion mutant isolation, and subsequent
identification and analysis are employed in model plants such as Arabidopsis
and in crop plants such as maize and rice.
||Pharmacogenetics investigates the different
reactions of human beings to drugs and the underlying genetic predispositions.
The differences in reaction are mainly caused by mutations in certain enzymes
responsible for drug metabolization. As a result, the degradation of the
active substance can lead to harmful by-products, or the drug might have
no effect at all.
||Pharmacogenomics makes use of the knowledge of the DNA sequences
for the development of new drugs.
||Shotgun genome sequencing is a sequencing strategy for which
parts of DNA are randomly sequenced. The sequences obtained have a considerable
overlap and by using appropriate computer software it is possible to compare
sequences and align them to build larger units of genetic information.
This sequencing strategy can be automated and leads to rapid sequencing
information, but it is less precise than a systematic sequencing approach.
||Single nucleotide polymorphisms (SNPs) are the most common type
of genetic variation. SNPs are stable mutations consisting of a change
at a single base in a DNA molecule. SNPs can be detected by HTP analyses,
for instance with DNA chips, and they are then mapped by DNA sequencing.