Birds and mammals have distinct sex chromosomes: in birds, males are ZZ and females ZW; in mammals, males are XY and females XX. By sequencing the chicken Z chromosome and comparing it with the human X chromosome, these authors overturn the currently held view that these chromosomes have diverged little from their autosomal progenitors. The Z and X chromosomes seem to have followed convergent evolutionary trajectories, despite evolving with opposite systems of heterogamety.

It has long been thought that motor control is achieved through the balanced activity of two distinct pathways througthe basal ganglia that have opposing effects, but this has never been functionally verified. These authors directly test this hypothesis with optogenetic activation of different populations of mouse striatal neurons, and not only trace functional connectivity but demonstrate opposing effects on motor behaviour in a parkinsonian model.

Ependymoma is a type of neural tumour that arises throughout the central nervous system. Using comparative transcriptomics in mouse and human tumours, these authors home in on mutations that are specific to individual tumour subgroups. In doing so, they generate the first mouse model of ependymoma and demonstrate the power of interspecific genomic comparisons to interrogate cancer subgroups.