Challagundla, Lavanya , Wallace, Lisa .
Evolution of B chromosomes in the genome of Xanthisma gracile (Asteraceae).
B chromosomes are unusual genetic elements that occur in addition to the normal chromosome complement of the A genome. B chromosomes have been found in 15% of eukaryotic species, most widely in flowering plants. The prevalence of B chromosomes in eukaryotic genomes in addition to variability in the mechanisms of action and perpetuation of B chromosomes across genomes creates many interesting questions about their origin and function within cells. In this project we have studied the origin of B chromosomes in the spiny daisy, Xanthisma gracile (Asteraceae) by comparing molecular genetic similarities between A and B chromosomes. Previous studies of X. gracile based on morphological, cytological and molecular genetic data suggest the possibility of interspecific hybridization with related species, which may have contributed to the origin of B chromosomes. Thus, we test the alternative hypotheses that the B chromosomes are derived from the A-genome vs. an external source through hybridization with a closely related species. Natural samples were collected from multiple populations in Arizona and seeds were germinated for experimental study. The DNA content of plants with and without B chromosomes was characterized using Flow Cytometry. Flow sorted chromosomes as well as regular metaphase chromosomes were used for FISH to assess the nature of B chromosomes using markers both from the A genome as well as related sister species. Patterns of heterochromatin relative to A chromosomes have been examined through G- banding which serves as an indicator of the presence of repeat regions. Flow cytometry indicated the cDNA content of X. gracile is~ 2 pg, which is consistent with recent reports but differs from the value in the Kew Database of Angiosperm C-values. The results of this study will be discussed in light of the evolutionary origin and diversification of X. gracile in relation to other closely related species and will lead to a better understanding of the molecular nature of its B chromosomes.
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1 - Mississippi State University, Biological Sciences, 34 N Wallace Circle, Mississippi State, MS, 39762, USA
2 - Mississippi State University, PO Box GY, Mississippi State, MS, 39762, USA
Presentation Type: Oral Paper:Papers for Sections
Location: Lindell C/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 11:00 AM