Genome mapping: clone maps made simple

Article Abstract:

The mapping of the human genome has received considerable attention, both as an interesting scientific enterprise and as a prototypical example of 'big' science. However, it still is not clear how best to break up the human genome, which consists of three billion base pairs, into chunks of manageable size. Now, a technique developed by Hans Lehrach and his colleagues shows promise as a relatively direct and non-labor intensive way to approach the problem of sequencing large genomes. It is easy to chop up the human genome into convenient pieces of about 40,000 bases per piece, but it is not easy to decide which end of what piece overlaps with another without laboriously sequencing each one. In other words, given many different pieces, how can they be assigned to a particular order? The answer rests in the laws of probability. A random probe of about 10 bases long will recognize a corresponding sequence in the larger piece by chance roughly half the time. Two unrelated pieces will match a random probe about one quarter of the time. However, if tested with more random probes, two pieces of DNA from the genome are likely to share the binding of several random probes only if they share some common sequence. For example, if DNA clone one shares some common sequence with clone two, and clone two shares some common sequence with clone three, but clone one shares nothing with clone three, then it is likely that clone two is located between clones one and three inside the genome, with overlapping ends. In the laboratory it is not possible to get the exact 50 percent probabilities which are desirable, and the task will require numerous DNA clones and long and tedious work. However, the principle has been already been applied successfully to bacterial genomes, and there seems to be no reason why it cannot be extrapolated to handle the human genome as well. (Consumer Summary produced by Reliance Medical Information, Inc.)

Nucleotide sequence, Base sequence, Genetics, editorial

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Mapping the way ahead

Article Abstract:

The Human Genome Project is publishing partial maps of the Y chromosome and of chromosome 21 in Oct 1992 that bring the Project closer to its objective of putting together a map of the entire human genome or genetic sequence. David Page and colleagues developed the Y chromosome map while Ilya Chumakov and colleagues produced the chromosome 21 map. Both research groups used cloned DNA to obtain the maps, indicating that this method is preferable to using restriction sites or recombination.

Research, Usage, Reports, Cloning

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Navigational progress

Article Abstract:

Information on the physical structure of genetic apparatus is given in great detail in the 'Genome Directory.' Many physical maps of the human genome are described in the book. Yeast artificial chromosome vectors are used to construct these maps. The maps are very useful in understanding the information content of the genome. The first sequence of the genome of a free-living organism could be used to study more complex human genome.

Criticism and interpretation, Literature, Genome Directory (Book)

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