ACCUMULATED VIROIDS. “The large chromosome size does not imply absence of genetic degeneration, nor a high expressed gene content. On the other hand, accumulation of repetitive sequences such as transposable elements on the Y does not necessarily imply degeneration. It may merely be a sign that recombination is rare.”
http://www.nature.com/hdy/journal/v95/n2/full/6800697a.html