Cytogenetics of Crotalaria

VIII. Male meiosis in 26 species

Abstract

Detailed male meiosis was studied in 26 species. Twenty three species were diploid (n=7, 8) and three were tetraploid (n=16). Various evidences show that basic number of the genus is eight.
Twenty diploid species had either 7 (C. incana) or 8 bivalents at diakinesis or metaphase I. The occurrence of 0-4 univalnets in a few cells in C. maxillaris and C. mucronata has been ascribed to early separation of synapsed homo/homoelogues and/or precocious separation of rod bivalents. The presence of 0-12 univalents in C. pallida (6.24/cell) has been attributed to asynapsis/desynapsis. Complete bivalent formation in three tetraploid species indicates their allopolyploid origin. The occurrence of non-random distribution of chiasmata in many species seems to be an important genetic factor. B chromosomes were recorded in 6 species.
Only in a few species abnormalities like late disjunction of bivalent/bivalents, lagging chromosomes, chromatin bridges with/without fragments were observed at anaphase I, II/telophase I, II.
It has been concluded that apart from gene mutations, important genetic factors like non-random distribution of chiasmata, reduced chiasma frequency, cryptic structural hybridity and paracentric inversions have played an important role in the evolution within the genus. Polyploidy has played a minor role.