In 1917, sex chromosomes in plants were discovered in a liverwort with hetermorphic U and V chromosomes. Such heteromorphy is unexpected because, unlike the XY chromosomes in diploid‐dominant plants, in haploid‐dominant plants the female U and the male V chromosomes experience largely symmetrical potential recombination environments. Here we use molecular cytogenetics and super‐resolution microscopy to study Frullania dilatata, a liverwort with one male and two female sex chromosomes. We applied a pipeline to Illumina sequences to detect abundant types of repetitive DNA and developed FISH probes to microscopically distinguish the sex chromosomes. We also determined the phenotypic population sex ratio because biased ratios have been reported from other liverworts with heteromorphic sex chromosomes. Populations had male‐biased sex ratios. The sex chromosomes are monocentric, and of 14 probes studied (eight satellites, five transposable elements and one plastid region), four resulted in unique signals that differentiated the sex chromosomes from the autosomes and from each other. One FISH probe selectively marked the centromeres of both U chromosomes, so we could prove that during meiosis each U chromosome associates with one of the opposite telomeres of the V chromosome, resulting in a head‐to‐head trivalent. The similarity of the two U chromosomes to each other in size and in their centromere FISH signal positions points to their origin via a non‐disjunction event (aneuploidy), which would fit with the general picture of sex chromosomes rarely crossing‐over and being prone to suffer from non‐disjunction.

中文翻译：

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地衣中的着丝粒组织和 UU/V 性染色体行为

1917 年，在具有异形 U 和 V 染色体的地衣中发现了植物中的性染色体。这种异形性是出乎意料的，因为与二倍体优势植物中的 XY 染色体不同，在单倍体优势植物中，雌性 U 和雄性 V 染色体经历了很大程度上对称的潜在重组环境。在这里，我们使用分子细胞遗传学和超分辨率显微镜来研究Frullania dilatata，一种具有一条男性和两条女性性染色体的地衣。我们将管道应用于 Illumina 序列以检测丰富类型的重复 DNA，并开发了 FISH 探针以在显微镜下区分性染色体。我们还确定了表型种群性别比，因为其他具有异形性染色体的苔类植物已经报道了偏差比。人口有偏向男性的性别比例。性染色体是单中心的，在研究的 14 个探针（8 个卫星、5 个转座元件和一个质体区域）中，4 个产生了独特的信号，将性染色体与常染色体和彼此区分开来。一个 FISH 探针选择性地标记了两条 U 染色体的着丝粒，因此我们可以证明在减数分裂期间每条 U 染色体都与 V 染色体的相反端粒之一相关联，导致头对头的三价。两条 U 染色体在大小和着丝粒 FISH 信号位置上的相似性通过非分离事件（非整倍性）指向它们的起源，这将符合性染色体很少交叉和容易发生的一般情况遭受不分离。