【求助】一个基本问题：miRNA家族

请问一下确定miRNAs属于一个miRNA家族的依据是什么？有没有相关阐述的文献？谢谢！

序列 的相似度？

microRNA family classification is based on the Rfam database (check the original paper on Rfam: http://nar.oxfordjournals.org/cgi/content/full/31/1/439 ). The basic idea behind family classification is that each family represens sequences that have evolved from a common ancestor.