逆转录病毒和逆转座子
逆转录转座子
When exactly this happened is still unknown, as this kind of analysis does not show when in evolutionary time the retroposons were inserted.
BBC: Australia's marsupials 'have American roots'
英汉双解词典包含3185865条英汉词条，基本涵盖了全部常用单词的翻译及用法，是英语学习的有利工具。