MEIOSIS, MITOSIS, AND THE INDUCTION OF CHROMOSOMAL ABNORMALITIES IN HYMENOLEPIS DIMINUTA BY GAMMA RAYS
Chromosomes of the adult stage of the cestode Hymenolepis diminuta are studied in aceto-orceia squashes of selected portions of the strobila. The details of odgenesis are observed and recorded; they are very similar to those for ther organisms. Oogonia increase in size and pass to the gin and function attaches itself to the primary oocyte. Reduction divisions proceed in a typical manner. Penetration of the oocyte by the sperm occurs prior to metaphase I. Male and female pronuclei do not fuse with each other, but remain separate during prophase. Their chromosomes mingle on the first cleavage spindle at metaphase. The cleavage pattern during the first six embryonic divisions is determined. The first five cleavage divisions of the embryo are unequal. The zygote appears to be subdivided by the cutting'' off of small cells from the main mass during these five divisions. An equal division occurs for the first time at cleavage VI and involves the largest cell of the embryo, as do the first five. The small cells formed during the early cleavages are of different sizes, depending upon the number of the division. The smaller cell formed by cleavage I is larger than those produced by the next three cell divisions of the embryo. There are twelve acrocentric chromosome s in metaphase plates. Chromosomes are of maximum size during the first few cleavage divisions, but become smaller as the large cell is reduced in size by the mitotic subdivision. The mitotic process is very precise with few, if any, irregularities in thousands of divisions. Mature worms are irradiated with gamma rays (400, 800, 1200, and 5000 r) by whole-body irradiation of rat hosts. Fixation times are 2, 7, 8, and 24 hours after the end of the irradiation period. As the dose of radiation increases, the number of embryos with aberrations also increases. Sticky'' chromosomes are found in worms examined soon after irradiation. Fragments and bridges appear in all material observed. Variations of chromosome number are noted. Chromosomes exceeding normal length are seen in. a few cells. Moderately long ones are probably a result of translocations. The extremely long chromosomes suggest a chromatid breakage-fusion-bridge cycle. A sample count of aberrations in the first five cleavage divisions are made in three worms receiving 5000 r. There are 451 embryos with chromosome alterations in 990 observed, or 45.5 per cent of the total. A greater percentage of these are found in cleavages III through V than are observed in the first two divisions. A growth rate study for H. diminuta in ten worm infestations is attempted for possible use in determining the number of cleavage divisions per given length of worm. The desired number of worms are not recovered from enough rats to establish a reliable growth curve.
- Research Organization:
- Univ. of Tennessee, Knoxville
- NSA Number:
- NSA-16-026791
- OSTI ID:
- 4796112
- Journal Information:
- Dissertation Abstr., Vol. Vol: 22; Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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