Paramutable possibilities

摘要

One of the benefits of sex is that our parents give us two copies of nearly all our genes, So if one copy, or allele, doesn't work, there is a good chance that the other, operating independently, will be sufficient. Exceptions exist, but even in thosecases the two alleles usually function independently. In rare cases, however, the alleles interact intimately, even though they reside on separate chromosomes, and whether one allele is expressed depends on directions given by the other. One example ofthis phenomenon is paramutation, a process in which orders issued by an allele in one generation are remembered in subsequent generations, even if the allele issuing the order is not transmitted. How do chromosomes remember who their partners were in previous generations, and how do those partners continue to exert their control long after they have segregated away? On page 469 of this issue, Minoo Rassoulzadegan et al, provide evidence for a mechanism involving small RNA molecules that might underlie paramutation.