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Please use this identifier to cite or link to this item: http://hdl.handle.net/1807/16732

Title: The Development and Evolution of Complex Patterns: The Drosophila Sex Comb as a Model System
Authors: Atallah, Joel Ramez
Advisor: Larsen, Ellen
Department: Cell and Systems Biology
Keywords: evolution
development
complexity
patterning
developmental constraints
Drosophila
sex comb
tarsus
bristle pattern
live imaging
convergent extension
cell intercalation
Issue Date: 19-Jan-2009
Abstract: One of the best-known structures in Drosophila is the sex comb, an arrangement of modified bristles on the tarsal forelegs of males. This complex, sexually-dimorphic trait shows striking variation among closely related species, although most other aspects of the tarsal bristle pattern have been conserved. I studied the development of the sex comb in the model organism Drosophila melanogaster and six related species. I confirmed that the D. melanogaster sex comb, although longitudinal in the adult, originates in a transverse orientation and rotates during development, and showed that this process occurs through male-specific convergent extension. However, in the species that I examined that have longitudinally-oriented sex combs that extend the full length of the tarsus, including D. ficusphila and two species of the montium subgroup, the sex comb does not rotate, and instead forms from two longitudinal rows that converge during development. Another species of the montium subgroup, D. nikananu, has a sex comb that is convergently similar to D. melanogaster, but forms in a manner typical of its subgroup, showing that very similar combs can be formed through different processes. In all species, there is a strong correlation between the position of the sex comb and the transverse bristle row on the foreleg tarsus just proximal to it. To test whether it is possible to violate this apparent constraint on development, I perturbed the expression of the leg patterning gene dachshund to generate ectopic sex combs in D. melanogaster. I found that while most patterns showed the same correlation, a few circumvent the constraint. I also demonstrated that the ectopic combs were formed non-autonomously and that overexpression of dachshund can transform certain aspects of the sex comb phenotype to resemble the transverse bristles to which they are homologous.
URI: http://hdl.handle.net/1807/16732
Appears in Collections:Doctoral
Department of Cell and Systems Biology - Doctoral theses

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