sentences:  Another example of structural variability is seen in vertebrates, in which 3 paralogues of subunits of the cyclin-dependent kinase module have evolved by 3 independent gene duplication events followed by sequence divergence.There is a report that mediator forms stable associations with a particular type of non-coding RNA, ncRNA-a.These stable associations have also been shown to regulate gene expression "in vivo", and are prevented by mutations in MED12 that produce the human disease FG syndrome.