Somatic pairing, reduction and recombination: an evolutionary hypothesis of meiosis.

Abstract

WITH the development of the concept that meaningful pairing of homologous chromosomes and crossing over occur only during meiotic prophase has come a series of reports of somatic pairing of homologous chromosomes in the Diptera1,2 and in Yucca3. Additional examples are random or predictable cases of metaphase and anaphase chromosome pairing and interphase-paired prochromosomes in flowering plants3,4 and in spermatogonia of various animals5,6. In some cases prochromosome reduction by pairing of presumed homologues occurs in tissues seen to have somatic pairing during mitosis7,9. The intimate association of homologous prochromosomes during interphase implies synapsis of euchromatic regions. Giant, interphase chromosomes of many Diptera are also synapsed during interphase. The occurrence of somatic recombination in fungi10 and in the flowering plant Arabidopsis11 (which evidently has somatic pairing throughout12) also indicates intimate interphase synapsis.