Meiosis: concluding remarks.

Abstract

Professor Darlington opened the meeting by challenging us with the view that chromosomes made the laws of heredity, rather than heredity fashioning the organization of chromosomes. To keep this wheel of logic spinning, it may be said that chromosomes also made the process of meiosis and thus determined the laws of meiotic exchange. I choose this gambit because our discussions lent considerable emphasis to the view that chromosome complexity compels its own sets of distinctive, and perhaps varied, mechanisms to effect the ultimate event of molecular recombination. The complexity that leads molecular recombination to operate in elaborate meiotic moulds is not, it should be emphasized, base sequence complexity. On the contrary, sequence repeats and genetic homoeologies, though adding disproportionately little to the base sequence complexity of a genome, adds considerably to the complexity of effecting chromosome alignment and crossing over. How chromosomes of diverse genetic content manage that complexity and in the process mould the characteristics of meiotic behaviour has been the primary target of our deliberations. That no single pattern of meiotic conduct was perceived in consequence of the discussions, is to be expected. To the extent that genomes differ in various aspects of chromosome organization - and that they do is patent - the particulars of meiotic organization might also differ. Although a strong sentiment was occasionally expressed for a single universal process of meiosis, it is my opinion that sameness and universality may be mistakenly treated as synonyms. Universals provide for diversity; they do not impose sameness. The task of identifying universal threads among different meiotic fabrics is not a straightforward one. The ultimate act of genetic recombination offers no detailed guide to the routes by which it may be achieved. Indeed, it is the structure of the chromosome that dictates the route ; recombination only signals the direction.