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. Despite various cost
associated with sex, sexual reproduction is widespread in natural populations. The causes of sexual reproduction,
however, are still obscure, and empirical data to resolve that paradox are scarce. Heteromorphic sex chromosomes
(i.e. the X and Y) are derived from a pair of ordinary autosomes. The Y chromosome is characterised by strongly
reduced levels of genetic activity, which is a direct consequence of its lack of recombination. Several species of the
genus Drosophila carry `neo-sex-chromosomes`, which have been formed by the fusion of an autosome with the
sex chromosomes. I propose to investigate the very recently evolved neo-Y chromosome of D. albomicans, which
shows little signs of degeneration. Using patterns of molecular evolution and variation at loci on the neo-sex
chromosomes I can study the initial stages in the evolution of a non-recombining genome. The proposal concerns
the following specific questions: (1) What is the age of this neo-sex chromosome system? (2) Is variability reduced
on the neo-Y chromosome? (3) Does the neo-Y chromosome show signs of reduced ability to adapt and maintain
its functional integrity? (4) Are transposable elements accumulating on the neo-Y chromosome? (5) To what
extend has the neo-X evolved dosage compensation?
This research will help to understand the causes of the degeneration of the non-recombining Y chromosome and
more generally, the adaptive significance of sexual recombination.