Bdelloid rotifer genomes contain two or more non-identical copies of each gene. This suggests their asexual reproduction is of long standing. For example, there are four copies of gene "hsp82". Each is different and on a different chromosome. This cannot be explaned by normal gene duplication, which produces two or more near-identical genes next to each other. By contrast, in a monogont rotifer, most genes were single-copy. 