Challagundla, Lavanya , Wallace, Lisa Ellen .
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 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, 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 genetic composition of B chromosomes was characterized by comparing sequences from individuals known to have B chromosomes against those lacking B chromosomes as well as related species of Xanthisma using PCR amplification, cloning, and sequencing of rDNA and phylogenetic analyses. As reported previously, we have identified variation in achene color that may be associated with the presence of B chromosomes. Patterns of heterochromatin relative to A chromosomes have been examined through G- banding which will serve as an indicator for the presence of repeat regions and lack of functional gene regions in B chromosomes. 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, P.O. Box GY, Mississippi State, , MS , 39762, USA
Presentation Type: Poster:Posters for Sections
Location: Hall A/Convention Center
Date: Monday, August 2nd, 2010
Time: 5:30 PM