In Wendy Bickmore's chap- ter, she has shown how extensions of fluorescent in situ hybridization can lead from a knowledge of cytogenetic changes in DNA to an analysis of chromosome dynamics during mitosis or chromatin remodeling. These are a vital feature, for example, of the famous cloning of the sheep Dolly. Naturally, the cytogenetic analyses must be accompanied by extensive biochemical studies of the protein components and their in- teractions. But as in the past, we can expect cytogenetic hints to lead the way toward later biochemical and physiological investigations. In Leonid Kruglyak's chapter, this variation is the raw material that is required for the study of the genetic factor in disease causation.
Variant sequences permit one to track down the genes that are participating in a process.
As he alludes to in his chapter, such genetic studies have already had many notable successes in explicating many single gene dis- eases. Although he emphasizes that the approach remains to be fully formulated and tested, I think that he subscribes to the general hope and optimism that the route he outlines will lead to a dramatic augmentation of the power to diagnose, anticipate, and perhaps alleviate complex chronic diseases. In general, the first world of geneticists now thinks in terms of the convergence of genomics and genetics and the exploitation of the result- ant functional analysis. These activities build on comparative studies of long-term changes in systems. Of course the twentieth was indeed the century of Watson and Crick and all of us whose works are footnotes to theirs.