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Gastrointestinal and liver diseases: genetic and epigenetic markers
  1. Hubert E Blum
  1. Department of Medicine II, University Hospital Freiburg, Freiburg, Germany
  1. Correspondence to Hubert E Blum, Department of Medicine II, University Hospital Freiburg, Hugstetter Strasse 55, D-79106 Freiburg, Germany; hubert.blum{at}uniklinik-freiburg.de

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Molecular analyses

The basic aspects of molecular, cell and stem cell biology are central to biomedical research and are increasingly becoming part of patient care in clinical practice (‘translational medicine’). The genetic material of humans is made up of DNA that in its entirety makes up an individual's genome that is structurally organised into 46 chromosomes (44 autosomes and two sex chromosomes XX or XY, defining the female or male phenotype). A seminal scientific achievement was deciphering the complete nucleotide sequence of the human genome by the concerted effort of the international human genome organisation project 10 years ago.1 2 This was followed by the era of ‘genomics’ that aim at unravelling the complete genetic information of an individual.3 In order to use the sequence information from genomics for research as well as for clinical applications and to define the function(s) of newly identified genes, strategies were developed to analyse globally genomic DNA sequences as well as their cell-, tissue- or organ-specific expression profiles that are collectively termed, ‘functional genomics’.

An important tool of functional genomics are array analyses, which are based on the complementary base pairing of single-stranded DNA or RNA (genes) to form a double-stranded hybrid (hybridisation). This principle has been used for several decades for the characterisation of DNA and RNA sequences, termed Southern or northern blot analyses, respectively. In contrast to these analytical tools which allow the simultaneous analysis of only a very limited number of DNA or RNA species, the recently developed array technologies now make it possible to simultaneously analyse huge numbers of DNA species or gene products (mRNA and proteins). Using chips, also termed ‘microarrays’ with a surface of about 0.5 cm2, thousands to tens of thousands of single-stranded DNA or reverse transcribed RNA (cDNA) species or oligonucleotides of known sequence can be …

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