报道说，此前，北极熊和灰熊曾在动物园内被配对成功，而且它们还生下了后代。 北极熊和灰熊这两种不同种类的熊，其繁殖期大致相同，但相比较而言，北极熊的繁殖期要比灰熊来得稍稍早一些。
Stirling said polar bears and grizzlies have been successfully paired in zoos and that their offspring are fertile, but there had been no documented case in the wild.
春天是它们的发情期，夜间啼血般地叫个不住，是召唤‘婚配对象’哩！
Spring is their estrus, the sound all time in night like crow blood is for beckoning their 'Mating objects'.
双线期时，配对的染色单体开始从四分体中分离，此时常可见染色体交叉。
In diplotene the pairs of chromatids begin to separate from the tetrad formed by the association of homologous chromosomes.
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