[aposiopetic]

Polyploidy is rarer in animals, which must sort out unmatched sex chromosomes, than in plants, which reproduce asexually as well as sexually. "But polyploidization is maintained over evolutionary time in vertebrates quite readily, although rarely. Recent examples, from the last 50 million years ago or so, include salmonids, goldfish, Xenopus [frogs], and a South American mouse," says Postlethwait.

Dumb question on my part: In general, duplication/polyploidization confers no particular advantage to sexually reproducing organisms, but may do so (or not confer disadvantage) in certain instances?

[jennyp]

Dumb question on my part: In general, duplication/polyploidization confers no particular advantage to sexually reproducing organisms, but may do so (or not confer disadvantage) in certain instances?

I think it's mostly that the polyploid offspring, if they survived, would never find a compatible mate to produce offspring with. (Unlike in plants, which are more likely to find a compatible mate. See here for a good explanation of plant polyploidy.)