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Glossary molecular genetics and related techniques:
 
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 elegans.
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 Agrobacterium 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.

(Biotechnology and Development Monitor, No. 40, p. 5.)


Contributions to the Biotechnology and Development Monitor are not covered by any copyright. Exerpts may be translated or reproduced without prior permission (with exception of parts reproduced from third sources), with  acknowledgement of source.

 


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