秉氏环毛蚓(Pheretima pingi Stephenson)雄性生殖细胞减数分裂

MEIOSIS OF THE EARTHWORM—Pheretima pingi STEPHENSON (ANNELIDA, OLIGOCHAETA)

以秉氏环毛蚓雄性生殖细胞为实验材料,通过石蜡连续切片方法,对雄性生殖细胞的减数分裂进行了初步研究,并分折了雄性生殖细胞在精巢囊、贮精囊中从形成到成熟的过程。进一步了解秉氏环毛蚓的染色体数2n=8。这为促进蚯蚓生物学研究、人工养殖和综合利用,以及蚯蚓的远缘杂交和育种选种提供理论依据。

Meiosis studies were carded out with the reproductive cells of male organs of Pheretima pingi Stephenson. The chromosome number of Pheretima pingi is 2n=8. During interphase, the cell shows a nucleus that is recognizable as a dark and rounded body. Its stainable material is dispersed in a fine network, in which chromosomes cannot recognized. During prophase of the first division the chromosomes appear as thin threads, a stage referred to as leptotent stage. In the zyotene stage, homologous chromosomes then come together side by side in pairs, in synapsis, but it is very difficult at this time to distinguish the number of chromosomes. These chromosomes then contract and thicken in pachytene stage. In this stage, it is usually evident that each chromosome has split lengthwise, except at the centromere. In diplotene stage, one strand may lie across another chromatid at the point of contact, that is a chiasma. Homologous chromosomes repel each other now. In diakinesis stage, the chromosomes become shorter, denser, and more clearly recognizable as separate bivalent units. In the metaphase of the first meiotic division, the tetrads line up at the equator of the cell. The tetrads break apart into dyads, each consisting of two chromatids, and these move to opposite poles of the spindle. At that time, the two strands of the dyad are still held together by a centromere. By the use of the spindle fiber, in anaphase, the two strands of the dyad depart from the centromere and move to opposite poles of the spindle. Two secondary spermatocytes form and separate in the telophase. The second division is the same as general mitosis.