Drosophila melanogaster chromosome 4 is an anomaly because of its small size, chromatin structure, and most notably its lack of crossing over during meiosis. Earlier ideas about the absence of crossovers on 4 hypothesize that these unique characteristics function to prevent crossovers. Here, we explore hypotheses about the absence of crossovers on 4, how these have been addressed, and new insights into the mechanism behind this suppression. We review recently published results that indicate that global crossover patterning, in particular the centromere effect, make a major contribution to the prevention of crossovers on 4.

中文翻译：

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黑腹果蝇第4号染色体上没有交叉：不完美还是有趣的例外？

果蝇的第4号染色体是一个异常，因为它的大小，染色质结构小，最显着的是它在减数分裂过程中没有交叉。早期关于在4上不存在交叉的想法认为，这些独特的功能可以防止交叉。在这里，我们探讨了关于4上不存在交叉的假设，如何解决这些交叉以及对这种抑制背后的机制的新见解。我们回顾了最近发表的结果，这些结果表明，全球交叉格局，尤其是着丝粒效应，对预防4的交叉做出了重大贡献。