Although sex chromosomes have evolved independently in many taxa, they are overall very similar, suggesting broadly similar evolutionary pathways. In particular, the acquisition of a male-determining gene on the proto-Y chromosome (or a female-determining gene on the proto W, in the case of female heterogamety) is quickly followed by the loss of recombination and consequent degeneration of genes on this newly formed Y/W chromosome. In XY systems, this is coupled with the acquisition of dosage compensation mechanisms that increase the expression of X-linked genes in males, to compensate for the missing (or non-functional) Y-linked copy. Given the similarities between the degenerated Y and W chromosomes, one would expect to find such dosage compensation mechanisms in ZW females, as W-linked copies of genes are also often missing or non-functional. However, the two independently evolved ZW systems that have so far been studied in detail, birds and Lepidoptera, lack dosage compensation. Although absence of dosage compensation may be a general feature of female-heterogametic species, it is also possible that the absence of DC mechanisms in these two clades is a mere coincidence, and the analysis of other independently evolved ZW systems is needed to confirm the pattern. We are analysing an independently evolved ZW system to test for this: Tephritids are dipteran insects closely related to Drosophila of which one genus, Tephritis, has a conserved ZW system. We are using Illumina sequencing to sequence the transcriptome of Tephritis species caught in the wild, in order to compare Z-linked and autosomal expression in males and females. If dosage compensation mechanisms are absent in these species, we expect ZW females, but not ZZ males, to show decreased Z-linked expression relative to the autosomal expression.
University of Edinburgh, UK – PhD in Evolutionary Biology, 2008
Federal University of Rio de Janeiro, Brazil – Bachelor Degree in Genetics, 2003
Dosage compensation in Female-heterogametic species We are sequencing the transcriptome of males and females of heterogametic species to test for the presence of dosage compensation in these ZW systems.
X-chromosome evolution in Drosophila (2004-2008) PhD research project, supervised by Prof. B. Charlesworth and Dr. P. Haddrill: We compared coding sequences from different species of Drosophila to test if the X chromosome has higher rates of adaptive evolution than the autosomes (Faster-X), and computed theoretically which conditions can lead to faster-X evolution. The accumulation of sex-biased genes on the D. melanogaster X chromosome was also investigated theoretically and using published expression data.
The birth of new genes on the D. melanogaster Y chromosome (2003) Undergraduate Research project, supervised by Prof. A.B. Carvalho: By blasting a set of proteins against the unassembled fraction of the D. melanogaster genome, potential Y-linked genes were identified, and experimentally tested for sex-linkage.
Vicoso, B. and Bachtrog, D. (2009) Progress and prospects toward our understanding of the evolution of dosage compensation. Chromosome Research 17(5).
Vicoso, B. and Charlesworth, B. (2009) Effective population size and the Faster-X Effect: an Extended Model. Evolution 63(9):2413-26.
Mank, J., Vicoso, B., Berlin, S. and Charlesworth, B. Effective population size and the Faster-X Effect: Empirical Results and their Interpretation. Evolution PMID: 19796145
Vicoso, B. Charlesworth, B. (2009) The deficit of male-biased genes on the D. melanogaster X is expression-dependent: a consequence of dosage compensation? J Mol Evol. 68(5):576-83.
Vicoso, B., Charlesworth, B. (2009) Recombination may affect polymorphism levels on the X and the autosomes in African populations of Drosophila. Genetics 181(4):1699-701.
Vicoso, B., Haddrill, P.R., Charlesworth, B. (2008) A multi-species approach for comparing sequence evolution of X-linked and autosomal sites in Drosophila. Genetics Research, Genetics Research 90:421-431.
Vicoso B, Charlesworth B (2006) Evolution on the X chromosome: unusual patterns and processes. Nat Rev Genet 7: 645–653.