Doris Bachtrog
e-mail:
dbachtrog@ucsd.edu |
 |
My main research interest
is in the evolutionary significance of sex and recombination
and its
implications for the mode and tempo of genome evolution. Questions
of interest to me include: Why is recombination so prevalent in
eukaryotes? Why do non-recombining parts of the genome in sexual
species, like the Y chromosome, degenerate? How do patterns of
genome evolution and genome-wide expression-levels respond to changes
in genome architecture and recombination rate? How does dosage
compensation evolve?
Most of my work involves using Drosophila as a model. With the
forthcoming completion of the entire genome sequence of 12 different
Drosophila species, combined with the wealth of genetic tools available,
Drosophila provides an ideal system to answer evolutionary genomics
questions using a comparative framework. I use several different
approaches in my research, combining molecular and computational
genomics techniques, comparative and functional genomics approaches,
theoretical modeling and experimental tests. Current research focuses
on the following areas:
The causes of Y chromosome degeneration.
It is generally believed that the advantage of sex lies in the associated process
of genetic recombination during meiosis, which constitutes the main difference
between sexual and asexual reproduction. Asexual species of eukaryotes seem
to go extinct at a higher rate than their sexual relatives. Likewise, non-recombining
parts of the genome in sexual species are prone to degeneration: X and Y
chromosomes are derived from a pair of ordinary autosomes, and the lack of
recombination on the Y chromosome has resulted in its degeneration. The non-recombining
portion of Y chromosomes is characterized by a paucity of active genes and
an abundance of repetitive sequences. I am using comparative genomics approaches,
population genetics and molecular genetic approaches to study the forces
responsible for Y chromosome degeneration in Drosophila, using three model
species: D. miranda, D. albomicans and D. athabasca. These species all have
Y chromosomes that were formed very recently on an evolutionary time scale,
allowing us to study the process of Y chromosome degeneration in action.
The evolution of gene expression and dosage compensation.
The degeneration of the Y chromosome creates the problem of reduced
gene-dosage of X-linked genes in males, resulting in the evolution
of dosage-compensation mechanisms. Dramatically different dosage-compensation
mechanisms have evolved in different organisms: Mammals inactivate
one of their two X chromosomes in females, XX hermaphrodite C.
elegans effectively halve the expression from each X, and male
Drosophila increase the transcription of their single X approximately
twofold. Large parts of the neo-Y chromosome in D. miranda show
various signs of degeneration, and some parts of the neo-X already
recruit the molecular machinery necessary for dosage compensation.
Using a library of tools from comparative genomics, population
genetics to gene expression studies, I investigate how gene expression
patterns evolve on these newly formed sex chromosomes, and, in
particular, the evolution of dosage compensation.
Adaptation in asexual genomes.
All natural populations have to adapt to new environments. Despite
its importance, the process of adaptation is far from being understood.
I am carrying out theoretical and experimental evolution studies,
to investigate the process of adaptation in asexuals. On a non-recombining
genome, like in asexuals or the Y chromosome, deleterious mutations
can considerably reduce the rate of fixation of advantageous
alleles. In collaboration with Dr. I. Gordo (Institute Gulbenkian
of Science, Portugal), I am performing theoretical investigations
and simulation studies of the population genetics of adaptation
in asexual populations. I am testing predictions of these models
using an experimental evolution approach.
Mammals with clonal chromosomes.
In most mammals, females have two X chromosomes, and males have
an X and a Y chromosome (XX vs. XY). However, some rodents have
very unusual sex chromosome systems. In the creeping vole, Microtus
oregoni, males are XY and females are X0 while in the mole vole,
Ellobius lutescens, both males and females are X0. Thus, the
X chromosome in these species is completely sheltered from recombination.
Using population genetics and molecular evolution approaches,
I am investigating the evolutionary origin of these bizarre sex
chromosome systems.
Bachtrog, D. (2004). Evidence that positive selection drives Y-chromosome degeneration in Drosophila miranda. Nature Genetics 36(5): 518-522.
Bachtrog, D. & I. Gordo. (2004). Adaptive evolution of asexual populations under Muller’s ratchet. Evolution 58(7):, 1403-1413.
Bachtrog, D. (2003). Protein evolution and codon usage bias on the neo-sex chromosomes of Drosophila miranda. Genetics, 165: 1221-1232.
Bachtrog, D. (2003). Adaptation shapes patterns of genome evolution on sexual and asexual chromosomes in Drosophila. Nature Genetics, 34 (2): 215-219.
Bachtrog, D. (2003). Accumulation of spock and worf, two novel retrotransposons, on the neo-Y chromosome of Drosophila miranda. Molecular Biology and Evolution, 20 (2): 173-181.
Bachtrog, D. & B. Charlesworth (2002). Reduced adaptation on a non-recombining neo-Y chromosome. Nature, 416 (6878): 323-326.
Bachtrog, D. & B. Charlesworth (2001). Towards a complete sequence of the human Y chromosome. Genome Biology, 2 (5):1016.1-1016.5.
Bachtrog, D. & B.
Charlesworth (2000). Reduced levels of microsatellite variability
on the neo-Y chromosome of Drosophila
miranda. Current
Biology, 10 (17): 1025-1031.
Doris Bachtrog received her M.Sc. in Genetics from the University of Vienna in 1999 and completed her Ph.D. at the University of Edinburgh in 2002 as a Marie Curie Fellow. She was a European Molecular Biology Organization Postdoctoral Fellow at the University of Edinburgh from 2002-2003, and an Austrian Academy of Science Postdoctoral Fellow at Cornell University from 2003-2004. Doris was recently awarded The Young Investigator's Prize from the American Society of Naturalists.