Blackman R L, Spence J M
Department of Entomology, Natural History Museum, London, UK.
Chromosome Res. 1996 Jun;4(4):314-20. doi: 10.1007/BF02263684.
The ribosomal DNA arrays in the nucleolar organizer regions (NORs) of aphids are generally-located in a telomeric or subtelomeric position on the X chromosomes. In aphid populations or species that have lost the sexual part of their life cycle and become permanent apomicts, multiple rDNA copies are often concentrated on only one of the original X chromosomes. This situation has been found in apomictic members of three aphid subfamilies, although not as yet in the tribe Aphidini, which includes several permanent apomicts that are important pests. Some clonal cultures of Acyrthosiphon pisum and Myzus persicae reared for many years in conditions that prolong apomixis and inhibit sexual reproduction also have their rDNA arrays concentrated on one X chromosome. A 50-year-old clone of Aphis fabae, however, still retains a pair of similar-sized rDNA arrays on its X chromosomes. Although pairing of the X chromosomes by their NORs during prophase of the maturation division seems to be required for determination of XO males in aphids, a clone of A. pisum with one rDNA array was nevertheless able to produce males when subjected to appropriate environmental conditions.
蚜虫核仁组织区（NORs）中的核糖体DNA阵列通常位于X染色体的端粒或亚端粒位置。在已经失去生命周期中有性阶段并成为永久性无融合生殖体的蚜虫种群或物种中，多个核糖体DNA拷贝通常仅集中在一条原始X染色体上。这种情况在三个蚜虫亚科的无融合生殖成员中都有发现，不过在蚜族中尚未发现，蚜族包括几种作为重要害虫的永久性无融合生殖体。在延长无融合生殖并抑制有性生殖的条件下饲养多年的一些豌豆蚜和桃蚜的克隆培养物，其核糖体DNA阵列也集中在一条X染色体上。然而，一种已有50年历史的豆蚜克隆在其X染色体上仍保留着一对大小相似的核糖体DNA阵列。虽然在成熟分裂前期通过NORs对X染色体进行配对似乎是蚜虫中XO雄性确定所必需的，但一个具有一个核糖体DNA阵列的豌豆蚜克隆在受到适当环境条件影响时仍能够产生雄性。
