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Rates of movement and distribution of transposable elements in Drosophila melanogaster: in situ hybridization vs Southern blotting data

Published online by Cambridge University Press:  23 October 2001

XULIO MASIDE
Affiliation:
Institute for Cell, Animal and Population Biology, University of Edinburgh, Ashworth Laboratories, Edinburgh EH9 3JT, UK
CAROLINA BARTOLOMÉ
Affiliation:
Institute for Cell, Animal and Population Biology, University of Edinburgh, Ashworth Laboratories, Edinburgh EH9 3JT, UK
STAVROULA ASSIMACOPOULOS
Affiliation:
Department of Pharmacology and Physiology, University of Chicago, Chicago, IL 60637, USA
BRIAN CHARLESWORTH
Affiliation:
Institute for Cell, Animal and Population Biology, University of Edinburgh, Ashworth Laboratories, Edinburgh EH9 3JT, UK
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Abstract

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Genomic copy numbers and the rates of movement of nine families of transposable elements (TEs) of Drosophila melanogaster were estimated in two sets of mutation accumulation lines: Beltsville and Madrid. Southern blotting was used to screen a large number of samples from both genetic backgrounds for TEs. The Madrid lines were also screened by in situ hybridization of TEs to polytene chromosomes, in order to obtain more detailed information about the behaviour of TEs in the euchromatin. Southern blotting data provided evidence of insertions and excision events in both genetic backgrounds, occurring at rates of approximately 10−5 and 10−6 per element copy per generation, respectively. In contrast, in situ data from the Madrid background presented a completely different picture, with no evidence for excisions, and a significantly higher rate of transposition (1·01×10−4). Direct comparison of the two data sets suggests that the Southern blotting technique had serious deficiencies: (i) it underestimated element abundance; (ii) it revealed less than 30% of the new insertions detected by in situ hybridization; and (iii) changes in the size of restriction fragments from any source were spuriously identified as simultaneous insertion–excision events. Our in situ data are consistent with previous studies, and suggest that selection is the main force controlling element spread by transposition.

Type
Research Article
Copyright
© 2001 Cambridge University Press