subsequently be used to map the putative gene to a chromosomal region or be used
itself as a probe to search a genomic DNA library for the remaining parts of the gene.
This type of information can be visualised using bioinformatics and useful infor-
mation determined in a process termed data mining. Much interest currently lies in
ESTs since they may represent a short cut to gene discovery.
A further gene isolation system that uses adapted vectors, termedexon trappingor
exon amplification, may be used to identify exon sequences. Exon trapping requires
the use of a specialised expression vector that will accept fragments of genomic DNA
containing sequences for splicing reactions to take place. Following transfection of a
eukaryotic cell line a transcript is produced that may be detected by using specific
primers in a RT–PCR. This indicates the nature of the foreign DNA by virtue of the
splicing sequences present. A list of further techniques that aid in the identification of
a potential gene-encoding sequence is indicated in Table 6.7.6.9.3 Genome mapping projects
As a result of the technological advances in large-scale DNA sequencing as indicated
in Chapter 5 it is now possible not only to map genomes of various species but also to
determine their sequence reliably and rapidly. The genomes of hundreds of species
have been determined and this is increasing each month. Sequencing and mapping of
the human genome was completed ahead of schedule and has provided many new
insights into gene function and gene regulation. It was also a multi-collaboration
effort that engaged many scientific research groups around the world and has given
rise to many scientific, technical, financial and ethical debates. One interesting issue is
the sequencing of the whole genome in relation to the coding sequences. Much of the
human genome appears to be non-coding and composed of repetitive sequences.Characterise disease phenotypeIdentify marker linked to geneIsolate disease gene by mappingIdentify and characterise disease geneIdentify function of protein encoded by geneFig. 6.50The scheme of identification of a disease gene by positional cloning.258 Recombinant DNA and genetic analysis