HUSSAIN, Sofia/M; LIVINGSTON, Brian/T; Univ of South Florida; Univ of South Florida: Variation within repetitive coding sequences between closely related species and within populations

Repetitive sequences often undergo concerted evolution, which can lead to both homogenization of the repeat sequences and variation in the number of repeat units. Within a given species, the number of repeat units is thought to be uniform because gene conversion rapidly eliminates all but one form of the gene. Little is known, however, about the frequency of concerted evolution within a species or population and the mechanisms involved. We have studied a sea urchin spicule matrix gene (SM50), that contains a series of imperfect repeats within the coding region. The repeat regions have undergone concerted evolution, leading to homogenization and length variation in a number of species examined. This homogenization has been balanced by varying degrees of substitutions within each species. Our studies have allowed us to predict how sequence variation might effect the mechanisms of concerted evolution. Here we test those predictions by examining the sequence of SM50 repeats within closely related species, and have found results that confirm our predictions. We also have begun to examine the frequency of concerted evolution events by sequencing the SM50 gene from a number of individuals from single species. We find little variation in the complex SM50 repeats in populations of Strongylocentrotus purpuratus, but we have found variation in a simple trinucleotide repeat found in the same gene. Similar studies are currently being carried out in species with less complex SM50 repeats.