Abstract
The haploid number of chromosomes in S. hjertingii Hawkes is found to be 24 (n=24) and is therefore tetraploid. The average chiasma frequencies per bivalent at diplotene and diakinesis were 1.69 and 1.27 respectively.The incidence of quadrivalents in the tetraploid species investigated is high (80.00%) indicating that they are autotetraploid with a high degree of affinity between four sets of chromosomes.The percentage of univalents is low (2.50%). Its occurrence in tetraploid may be due to genetic dissimilarity of individual chromosomes or mechanical interference with pairing due to presence of four sets of homologous chromosomes. Their behaviours cause unequal distribution of chromosomes in second metaphase plates. Univelents and fragments which failed to be included in the daughter nuclei formed micronuclei (2.86 %).The frequency of chromatid bridge is 3.83%. There is no relationship between the chromatid bridge and deformity of pollen in S. hjertingii. The strong homology between the four sets of chromosomes indicates an autopolyploid origin. This shows that polyploidy plays a major role in their evolution.
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