The coexistence of discrete morphs that differ in multiple traits is common within natural populations of many taxa. Such morphs are often associated with chromosomal inversions, presumably because the recombination suppressing effects of inversions help maintain alternate adaptive combinations of alleles across the multiple loci affecting these traits. However, inversions can also harbour selected mutations at their breakpoints, leading to their rise in frequency in addition to (or independent from) their role in recombination suppression. In this review, we first describe the different ways that breakpoints can create mutations. We then critically examine the evidence for the breakpoint-mutation and recombination suppression hypotheses for explaining the existence of discrete morphs associated with chromosomal inversions. We find that the evidence that inversions are favoured due to recombination suppression is often indirect. The evidence that breakpoints harbour mutations that are adaptive is also largely indirect, with the characterization of inversion breakpoints at the sequence level being incomplete in most systems. Direct tests of the role of suppressed recombination and breakpoint mutations in inversion evolution are thus needed. Finally, we emphasize how the two hypotheses of recombination suppression and breakpoint mutation can act in conjunction, with implications for understanding the emergence of supergenes and their evolutionary dynamics. We conclude by discussing how breakpoint characterization could improve our understanding of complex, discrete phenotypic forms in nature.

中文翻译：

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反转断点和超基因的进化

在许多类群的自然种群中，具有多种性状不同的离散形态共存是很常见的。这种变形通常与染色体倒位有关，大概是因为倒位的重组抑制作用有助于在影响这些性状的多个基因座上维持等位基因的交替适应性组合。然而，倒位也可以在其断点处隐藏选定的突变，除了（或独立于）其在重组抑制中的作用之外，还导致其频率上升。在这篇综述中，我们首先描述断点创建突变的不同方式。然后，我们批判性地检查断点突变和重组抑制假设的证据，以解释与染色体倒位相关的离散变形的存在。我们发现，由于重组抑制而有利于倒位的证据通常是间接的。断点包含适应性突变的证据在很大程度上也是间接的，在大多数系统中，序列水平上的反转断点的表征是不完整的。因此需要直接测试抑制重组和断​​点突变在反转进化中的作用。最后，我们强调重组抑制和断点突变这两个假设如何协同作用，这对于理解超基因的出现及其进化动力学具有重要意义。最后，我们讨论断点表征如何提高我们对自然界复杂、离散表型形式的理解。