In the general model of sex chromosome evolution for diploid dioecious organisms, the Y (or W) chromosome is derived, while the homogametic sex presumably represents the ancestral condition. However, in the frog species Quasipaa boulengeri, heteromorphisms caused by a translocation between chromosomes 1 and 6 are not related to sex, because the same heteromorphic chromosomes are found both in males and females at the cytological level. To confirm whether those heteromorphisms are unrelated to sex, a sex-linked locus was mapped at the chromosomal level and sequenced to identify any haplotype difference between sexes. Chromosome 1 was assigned to the sex chromosome pair by mapping the sex-linked locus. X-chromosome translocation was demonstrated and confirmed by the karyotypes of the progeny. Translocation heteromorphisms were involved in normal and translocated X chromosomes in the rearranged populations. Based on phylogenetic inference using both male and female sex-linked haplotypes, recombination was suppressed not only between the Y and normal X chromosomes, respectively the Y and translocated X chromosomes, but also between the normal and translocated X chromosomes. Both males and females shared not only the same translocation heteromorphisms but also the X chromosomal dimorphisms in this frog. The reverse of the typical situation, in which the X is derived and the Y has remained unchanged, is known to be very rare. In the present study, X-chromosome translocation has been known to cause sex chromosomal dimorphisms. The X chromosome has gone processes of genetic differentiation and/or structural changes by chance, which may facilitate sex chromosome differentiation. These sex chromosomal dimorphisms presenting in both sexes may represent the early stages of sex chromosome differentiation and aid in understanding sex chromosome evolution.

中文翻译：

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多刺蛙 (Quasipaa boulengeri) 中 X 染色体易位所描述的性染色体二态性

在二倍体雌雄异体生物的性染色体进化的一般模型中，Y（或W）染色体是衍生出来的，而同配子性别可能代表了祖先的条件。然而，在蛙类 Quasipaa boulengeri 中，由 1 号和 6 号染色体之间的易位引起的异型性与性别无关，因为在细胞学水平上，雄性和雌性中都发现了相同的异型染色体。为了确认这些异态性是否与性别无关，在染色体水平上绘制了一个与性别相关的基因座，并对其进行测序以识别性别之间的任何单倍型差异。通过绘制性连锁基因座，将染色体 1 分配给性染色体对。X染色体易位通过后代的核型得到证实和证实。易位异态性与重排种群中的正常和易位 X 染色体有关。基于使用男性和女性性连锁单倍型的系统发育推断，不仅在 Y 和正常 X 染色体之间，分别在 Y 和易位 X 染色体之间，而且在正常和易位 X 染色体之间，重组都受到抑制。在这只青蛙中，雄性和雌性不仅具有相同的易位异型性，而且还具有 X 染色体二态性。众所周知，与典型情况相反的情况非常罕见，即 X 是派生出来的，而 Y 保持不变。在本研究中，已知 X 染色体易位会导致性染色体二态性。X染色体偶然经历了遗传分化和/或结构变化的过程，这可能有助于性染色体分化。这些在两性中出现的性染色体二态性可能代表性染色体分化的早期阶段，有助于理解性染色体的进化。