The sex chromosome that refused to die

Abstract

Chromosomes that harbor dominant sex determination loci are predicted to erode over time--losing genes, accumulating transposable elements, degenerating into a functional wasteland and ultimately becoming extinct. The Drosophila melanogaster Y chromosome is fairly far along this path to oblivion. The few genes on largely heterochromatic Y chromosome are required for spermatocyte-specific functions, but have no role in other tissues. Surprisingly, a recent paper shows that divergent Y chromosomes can substantially influence gene expression throughout the D. melanogaster genome.1 These results show that variation on Y has an important influence on the deployment of the genome.

Figure 1

Crossing scheme used to produce population-specific Y chromosomes introgressed into a common isogenic background. Males from five different fly populations (Y₄₃₆₁, Y_mass, Y_Ohio, Y_Mass, Y_Zimbab) were each crossed with females that had recessive markers on each chromosome (strain number 4361- y=yellow on X chromosome; bw=brown on chromosome 2; e=ebony on chromosome 3; ci=cubitus interrupts on chromosome 4 and ey=eyeless on chromosome 4). In the first generation (G1), all flies were heterozygous and theseG1maleswere then backcrossed with females. Males homozygous recessive for all markers and that contained population-specific Y chromosomes were then selected for gene expression analysis.