Chromosomal and molecular evolution in the genus Brachyscome (Asteraceae)

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Chromosome number determination s form 145 populations attributed to 29 species or species complexes of Brachyscome are made. First reports for 6 species and new reports for two species are presented. Remaining counts support previously reported determinations and add to knowledge of chromoso me number distribution. Karyotype analyses. are sade on 30 iaxa at Nitoticmetaphase and 25 taxs at mltotic prometaphase. Two groups are distinguished by the total size of haploid chromosome set. In the hybrids from three cross combinations between aboye two groups there are marked differences or asynchrony in the condensation patterns of the chromosomes from the two Parental sources. lt is, however, remained whether they are monophyletic or not, respectlyely. In above two groups the total size of haplold chromosome set are not correlated with chromosome number, rather constant from n=9 to 2. There is no general trend toward asymmetry of karyotype during evolution in Brachyscome. Total DNAs extract … More ed from 19 taxa were digeited with 12 endonucleases. DNA fragments were separated on 1.0% agarose gels, denatured and transferred to a nylon membrane. For hybridizations I used cpDNA from tobacco. Mutations were polarized using a suite of closely related outgroup, the genus Aster. Seventeen synapomorphic site mutations were detected. Phylogenetic reconstruction of 19 taxa used Wagner persisony and the computer Program PAUP package to find the shortest phylogenetic tree. This phylogenetic tree indicats the increase in chromosome number from n=4 to 5, 6 and 9 rather than the decrease, except from n=4 to 3. These data suggest the following chromosomal evolution in this genus ; 1)the reduction in chromosome number from n=9 to 4 has occurred drastically and then the species with the intermediate chromosome numbers have been extinct. 2)the secondary speciation has been occurred explosively at the n=4 level. 3)the extant species with n=5, 6, 7, 8 and 9(in part)are the derivatives with the increase in chromosome number from n=4. Less