在我们研究的460种多根鞘翅目核型中,50(10.8%)是X染色体重排的携带者。除了有丝分裂中期分析,对减数分裂细胞进行了正确的诊断,主要在粗线质阶段。这些染色体间重排的百分比,主要是融合,相对于染色体的总二倍体数变化:高(51%)低于19,零在19,低(2.7%)在20(祖先和模态数),从7.1%到16.7%,从22到30以上略有增加。X在染色体融合中的参与似乎比常染色体平均值的预期高出七倍以上。显示了具有X常染色体重排的核型实例,包括在自动染色体中插入整个X(ins(A;X)),以前从未在动物中报道过。端到端融合(罗伯逊易位,终端重排,和伪二中心)是X自动体重排的最常见类型。与具有19,X公式的34种一样,在具有X常染色体重排的50个核型中没有Y染色体的痕迹,这证明了该染色体的可分配性。在大多数情况下,C带的异染色质存在于X常染色体连接处,这表明它将性腺与性腺部分隔离开来,其基因受到不同水平的表达。最后,提出X在染色体间重排中的非常优先的参与解释为:(1)X的频繁的肢端形态,因此组成性异染色质的末端位置,可以隔离附着的性腺和常染色体成分;(2)Y染色体的可分配性,这大大降低了男性减数分裂中杂合状态的有害后果,(3)随着无用的Y染色体的快速丢失,X常染色体-常染色体三价的正确分离,这当然是由其常染色体部分的交叉确保的。
Amongst the 460 karyotypes of Polyphagan Coleoptera that we studied, 50 (10.8%) were carriers of an X autosome rearrangement. In addition to mitotic metaphase analysis, the correct diagnosis was performed on meiotic cells, principally at the pachytene stage. The percentages of these inter-chromosomal rearrangements, principally fusions, varied in relation to the total diploid number of chromosomes: high (51%) below 19, null at 19, low (2.7%) at 20 (the ancestral and modal number), and slightly increasing from 7.1% to 16.7% from 22 to above 30. The involvement of the X in chromosome fusions appears to be more than seven-fold higher than expected for the average of the autosomes. Examples of karyotypes with X autosome rearrangements are shown, including insertion of the whole X in the autosome (ins(A;X)), which has never been reported before in animals. End-to-end fusions (Robertsonian translocations, terminal rearrangements, and pseudo-dicentrics) are the most frequent types of X autosome rearrangements. As in the 34 species with a 19,X formula, there was no trace of the Y chromosome in the 50 karyotypes with an X autosome rearrangement, which demonstrates the dispensability of this chromosome. In most instances, C-banded
heterochromatin was present at the X autosome junction, which suggests that it insulates the gonosome from the autosome portions, whose genes are subjected to different levels of expression. Finally, it is proposed that the very preferential involvement of the X in inter-chromosome rearrangements is explained by: (1) the frequent acrocentric morphology of the X, thus the terminal position of constitutive
heterochromatin, which can insulate the attached gonosomal and autosomal components; (2) the dispensability of the Y chromosome, which considerably minimizes the deleterious consequences of the heterozygous status in male meiosis, (3) following the rapid loss of the useless Y chromosome, the correct segregation of the X autosome-autosome trivalent, which ipso facto is ensured by a chiasma in its autosomal portion.