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The behavior of meiosis in sperm.

Although brewing for some time, a number of developments have quietly brought about a fundamental revolution in human genetics: our science is no longer a purely observational one, but, increasingly, is "experimental" as well. Two papers in this issue of theJournal that deal with multipoint genetic mapping in human sperm go a long way toward proving this point. In effect, some basic biological aspects of meiosis, the cornerstone of heredity, can now be directly revealed in the human and need not be extrapolated from other experimental organisms. This does not, however, diminish the importance of similar data from experimental crosses. The optimism outlined in the now classic paper by Botstein et al. (1980) that was published in the Journali.e., that a complete genetic linkage map of the human genome, based on DNA markers, could be constructedis now a firm reality. There have been many advances in molecular, statistical, and computational technologies along the way to enable this fundamental change, and complete genome linkage maps are available for a number of organisms. What is important, and in marked contrast to the past, is that the most comprehensive linkage map anywhere is in the human-an organism with many hurdles for genetic research. A very recent publication describes the identification and mapping of >2,000 highly polymorphic markers that can be rapidly assayed by PCR (Gyapay et al. 1994). This map provides a resolution of <3 cM, and considerably more markers are being generated by the efforts of a number of NIH-funded genome centers in the United States. The availability of this nouveau map means that any human chromosome and its homologue can now be accurately tracked from one generation to the next and that Mendel's laws with all their myriad consequences can be explored. Any individual can now be rapidly genotyped