The problem he encountered was that each time the cells divided , the mini-chromosomes degraded , until eventually they vanished completely .
他遇到的难题是,每当细胞分裂时,微型染色体就会退化,直到最终它们完全消失。
The sahel has been degraded by human use , not natural desertification ; the natural process has been the reverse .
撒哈拉草地的退化是人为的,与自然荒漠化无关;这一自然已经开始逆转。
Until now many researchers have argued that it would be impossible to sequence the entire genome of an extinct creature because the samples are so degraded .
They have increased to the point that both their tundra breeding areas and the saltmarsh wintering grounds are becoming severely degraded , and this is affecting other species using the same habitat .