Research objectives and content
Theoretical models show that transposable element (TE's) insertions at individual genomic sites are expected at lowfrequency as a result of an equilibrium between transpositional increase in element abundance and one or more opposing forces. High frequencies or fixation are expected only if element insertions have functional significance to their hosts. In Drosophila, the technique of in situ hybridization on the polytene chromosomes permits identification of sites occupied by TE's in chromosomes isolated from natural populations. The data on D. melanogaster unequivocally shows that the frequency of occupation of a given chromosomal site by a member of a particular family is nearly always very low. There is only a handful of exceptions, which form the subject of this proposal.
1- To determine whether (1) these apparently fixed insertions involve individual nucleotide sites or (2) reflect insertions at different locations within the same band. In situ hybridization permits the localisation of the insertions in terms of chromosome bands, being necessary a molecular approach in order to discriminate between this two alternative hypothesis.
2- If (1) is the case, to determine the causes of high element frequencies or fixation at an unique site. Molecular characterization of the insertion site will shed a light on the evolutionary forces that drove this insertions to high frequency or fixation .
Training content (objective, benefit and expected impact)
Objective: to improve my training in the following subjects: Molecular biology techniques: DNA handling, in situ and dot-blot hybridization, southern blotting, DNA cloning, PCR, DNA sequencing.
Other methods: DNA sequence analysis.
Theoretical population genetics training: The study of the nature of the forces that regulate TE abundance in thehost genome is crucial to understanding the organization and evolution of the genome, and therefore a most interesting task in evolutionary biology.
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