And,like birds they have a single opening with which they produce eggs, have sex and expel waste.

VOA: special.2009.07.07

The DNA molecule here has been spread apart, opening up two single stranded DNA's which have complementary base sequences because they were double stranded DNA.

这里DNA分子被分开,形成两条单链DNA,这两条单链碱基序列互补,因为它们是由双链DNA解旋形成的

耶鲁公开课 - 生物医学工程探索课程节选