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24 April 2014 11:45 am ,
Vol. 344 ,
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Millions around the world got a first-hand look at what it was like to be in Tacloban while it was pummeled by...
- 24 April 2014 11:45 am , Vol. 344 , #6182
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Higher Resolution Human Genome Map Finished
21 May 1997 (All day)
Genome researchers have put together the most complete map of the human genome yet. In this month's issue of Genome Research, Elizabeth Stewart and her colleagues at Stanford University present this new map, which places about 8000 landmarks along the genome's 3 billion bases--DNA's building blocks--yielding twice the resolution of gene maps currently in use.
Equally detailed maps have been produced for a few of the human genome's 23 chromosomes, but this map provides "placement of landmarks all across the genome," says Eric Green, a molecular biologist at the National Human Genome Research Institute in Bethesda, Maryland. Other genome maps have more landmarks, but not all of them have been positioned relative to every other landmark as they are in this map. And that makes it quite useful to gene mappers trying to fit in new markers or pinpoint genes involved in diseases, although the ultimate goal--sequencing the entire human genome--will require maps with four times as many landmarks.
The Stanford group didn't build its map one DNA landmark at a time, as do most gene mappers. Instead, the researchers took a statistical shortcut that enabled them to position many of these landmarks at once. To do this, they used an approach called radiation hybrid mapping. They first bombarded human DNA with x-rays, and then placed the 83 resulting fragments into different hamster cells. As those cells proliferated in laboratory dishes, the bits of human DNA were also copied, creating cell lines, each of which had a different fragment. To create the map, the researchers searched each cell line for particular known human DNA markers, keeping track of which markers appear in which cell lines. A computer program that analyzes the frequency of overlap between all the landmarks then placed them in order.
Now that they have shown that this approach works at this level of mapping detail, the Stanford group says it is working to make a new map that has 30,000 markers spaced about 100,000 bases apart. That sort of resolution should be good enough to determine the sequence of all the nucleotide bases in the human genetic code.