How to make a sex chromosome?

Sex chromosomes evolve from autosomes yet harbor many unique characteristics that differentiate them from autosomes and from each other. Male-specific Y chromosomes degenerate: they lose most of their protein-coding genes, accumulate repetitive DNA and often acquire a genetically inert heterochromatic structure. In response, X chromosomes often become dosage compensated, again involving epigenetic modifications .

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Young sex chromosomes found in many Drosophila species offer a unique opportunity to study the evolution and function of sex chromosomes caught in the act of diverging from autosomes and each other, while acquiring the distinct characteristics seen in older sex chromosomes. Our lab has been pioneering genome-wide comparative and functional analysis of sex chromosomes in Drosophila, including whole-genome sequencing and assembly, transcriptome and chromatin profiling across tissues and development, transgenics, and population genomics, to identify the molecular changes causing sex chromosome differentiation, and the evolutionary forces driving these changes. We have also developed powerful statistical methods for identifying sex-linked genes by sequencing that is applicable to virtually any organism, which has allowed us to study the functional and evolutionary properties of sex chromosomes in several non-model species, including birds, snakes and various insects, in an unprecedented way.

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Current work focuses on three fundamental outstanding questions about sex chromosomes:

How to make a species?

In the past few years, we have begun to pursue an entirely novel research direction: Which genes and genetic pathways contribute to the evolution of behavioral reproductive isolation? Understanding what drives the appearance of new species has been a key question in evolutionary biology for over a century. My lab has begun to identify genes involved in Drosophila courtship rituals that differ between closely related species. During courtship, Drosophila males emit sounds by vibrating their wings, and differences in this courtship song associated with female preferences for species-specific songs result in strong behavioral prezygotic isolation between Drosophila species. Additionally, chemical cues such as cuticular hydrocarbons are used as signaling molecules in mate recognition and communication. My lab has established fast and inexpensive methods to re-sequence fly genomes and high-throughput phenotyping methods and algorithms to measure male courtship songs and female behavior and cuticular hydrocarbon profiles in order to map genes associated with mate-choice in several Drosophila species.

Current work focuses on several different Drosophila systems:

  • Prezygotic isolation in the athabasca species group
  • Pre- and postzygotic isolation in the nasuta species complex
  • The evolution of hybrid swarms