Cytogenetic features of the hangingfly Bittacus sinicus Issiki, 1931 were investigated for the first time using C-banding and DAPI (4',6-diamidino-2-phenylindole) staining. The karyotype analyses show that the male B. sinicus possesses the lowest chromosome number (2n = 15) ever observed in Mecoptera, and an almost symmetric karyotype with MCA (Mean Centromeric Asymmetry) of 12.55 and CVCL (Coefficient of Variation of Chromosome Length) of 19.78. The chromosomes are either metacentric or submetacentric with their sizes decreasing gradually. Both the C-banding and DAPI+ patterns detect intermediate heterochromatin on the pachytene bivalents of B. sinicus, definitely different from the heterochromatic segment at one bivalent terminal of other bittacids studied previously. The male meiosis of B. sinicus is chiasmate with two chiasmata in metacentric bivalents and one in the submetacentric bivalent. The sex determination mechanism is X0(♂), which is likely plesiomorphic in Bittacidae. Two alternative scenarios of karyotype origin and evolution in Bittacus Latreille, 1805 are discussed.

中文翻译：

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悬挂蝇Bittacus sinicus（长翅目，Bittacidae）的高度重排核型：该目中染色体数目最低。

首次使用 C 显带和 DAPI（4',6-二脒-2-苯基吲哚）染色研究了悬挂蝇 Bittacus sinicus Issiki, 1931 的细胞遗传学特征。核型分析表明，雄性华氏B. sinicus拥有长翅目中迄今为止观察到的最低染色体数（2n = 15），且核型几乎对称，MCA（平均着丝粒不对称性）为12.55，CVCL（染色体长度变异系数）为19.78。染色体为中着丝粒或亚中着丝粒，其尺寸逐渐减小。C 带和 DAPI+ 模式均检测到 B. sinicus 粗线期二价体上的中间异染色质，这与之前研究的其他 bittacids 的一个二价末端的异染色质片段明显不同。中华双歧杆菌的雄性减数分裂是交叉的，其中两个交叉为中着丝粒二价体，一个交叉为亚中着丝粒二价体。性别决定机制是 X0(♂)，这可能与 Bittacidae 类似。讨论了 Bittacus Latreille, 1805 中核型起源和进化的两种替代方案。