11.   He had added a cancer gene, c-myc, to mouse embryos in an attempt to understand what the gene normally does.

12.   Human Genome Sciences found its genes by catching cells in the act of making the proteins, without knowing at first what the genes did.

13.   If it does, it is a simple matter to discover what the gene does in yeast, indicating its function in humans.

14.   It exploits statistical analysis and landmarks along chromosomes to zero in on target genes without prior knowledge about what the genes normally do.

15.   Merely sequencing the genetic code does not tell us what all the genes do or how the cells are formed.

16.   So scientists will have great difficulty figuring out what all those genes do and how they do it.

17.   The best the genes can do is indicate the rough layout of the wiring, the general shape of the brain.

18.   The challenge now is to figure out what the genes do.

19.   The idea is to learn what a gene does by excising it and seeing what defects the mouse develops.

20.   The next step, Todd said, is to find out what these genes actually do and to assess their relative contributions to diabetes.