Sex chromosomes arose independently several times in evolution from ordinary autosomal pairs by acquiring a sex determining region, followed by recombination suppression, accumulation of repeats and degeneration of genes. Despite much theoretical and empirical work to explain the convergent evolution of sex chromosomes across eukaryotes, we severely lack a detailed molecular view of how and what kind of sex-chromosomal changes occur over various evolutionary time scales. Addressing these fundamental gaps in our knowledge requires the study of young sex chromosome systems that differ among closely related species. To address these gap we used recently evolved sex chromosomes found in grasshoppers and birds, using comparative genomics, molecular biology and cytogenetics.