Meiotic chromosome

Mice exposed to 2,000 ppm of trichloroethylene, 4 hours/day for a 5-day period, had a significant increase in abnormal sperm morphology of 1% 28 days after the exposure (Land et al. 1981). No effect was seen at 200 ppm. A 6% increase in abnormal sperm was observed 4 weeks, but not 4 days or 10 weeks, after mice were exposed to 100 ppm trichloroethylene 7 hours per day for 5 days (Beliles et al. 1980). Based on the time after exposure at which sperm were affected, the study authors indicated that trichloroethylene damages sperm precursor cells but that spermatogonia were either unaffected or were capable of recovery. Reproductive performance was not tested in these studies. Another mouse study tested the effects of a 5-day exposure (6 hours/day) on spermatid micronuclei frequency no effects were observed at exposure levels of up to 500 ppm, the highest concentration tested (Allen et al. 1994). These results were interpreted as evidence that trichloroethylene did not cause meiotic chromosome breakage or loss. No treatment-related reproductive effects were seen in female rats exposed to 1,800 ppm trichloroethylene for 2 weeks (6 hours/day, 7 days/week) before mating (Dorfmueller et al. 1979). 

Clarke, H. J., and Masui, Y. (1983). The induction of reversible and irreversible chromosome decondensation by protein synthesis inhibition during meiotic maturation of mouse oocytes. Dev. Biol. 97 291-301. 

Goldstein LSI 980 Mechanisms of chromosome orientation revealed by two meiotic mutants in Drosophila melanogaster. Chromosoma 78 79-111... 

Uhlmann F, Lottspeich F, Nasmyth K 1999 Sister-chromatid separation at anaphase onset is promoted by cleavage of the cohesin subunit Sccl. Nature 400 37-42 vanHeemst D, James F, Poggeler S, Berteaux-Lecellier V, ZicklerD 1999 Spo76p is a conserved chromosome morphogenesis protein that links the mitotic and meiotic programs. Cell 98 261-271... 

Lehner There is a paper by Goldstein (1981) in which he describes electron microscope (EM) studies of meiotic chromosomes. At meiosis I, chromosomes do not have two sister kinetochores. There is a maturation into two kinetochores between the two meiotic divisions. Have comparable EM analyses been done in yeast ... 

Hunt I thought you could see Saccharomyces cerevisiae meiotic chromosomes quite nicely. 

Goldstein LS 1981 Kinetochore structure and its role in chromosome orientation during the first meiotic division in male D. melanogaster. Cell 25 591-602... 

Panda BB. 1983. Effect of the insecticides, oxydemeton, methyl and thiodemeton, on the mitotic and meiotic chromosomes of barley (Hordeum vulgare). Environ Exper Botany 23 293-296. 

H2A(.X) H2Av H2A.X Phosphorylation in DNA damage, Meiotic recombination, Mammals Meiotic Sex chromosome condensation RD/RI... 

Jain AK, Sarbhoy RK. 1987b. Cytogenetical studies on the effect of some chlorinated pesticides. II. Effect on meiotic chromosomes of Lens and Pisum. Cytologia 52 55-62. 

The first cell division of meiosis occurs in the primary oocyte but the process is arrested during prophase and remains so until puberty. Just before ovulation, meiosis, which has been arrested since before birth, resumes. The first division halves the number of chromosomes to produce the haploid secondary oocyte. The process is the same as that in spermatozoa (Chapter 20 see Figure 20.29 ) except that the two resulting haploid daughter cells are unequal in size. One is the large functional secondary oocyte whereas the other is much smaller and is known as the first polar body. The second meiotic division is arrested at metaphase. It is completed only at fertilisation. Once again, the division is unequal. One cell is large, the secondary oocyte. The other is small, a second polar body, which is discarded. 

Buso, J. A., Boiteux, L. S., Tai, G. C. C., Peloquin, S. J. (1999c). Chromosome regions between centromeres and proximal corssovers are the physical sites of major effect loci for yield in potato genetic analysis employing meiotic mutants. Proceedings of the National Academy of Science, USA 96, 1773-1778. 

After the DNA is replicated during prophase of the first meiotic division, the resulting sister chromatids remain associated at their centromeres. At this stage, each set of four homologous chromosomes exists as two pairs of chromatids. Genetic information is now exchanged between the closely associated homologous chromatids... 

Homologous recombination thus serves at least three identifiable functions (1) it contributes to the repair of several types of DNA damage (2) it provides, in eukaryotic cells, a transient physical link between chromatids that promotes the orderly segregation of chromosomes at the first meiotic cell division and (3) it enhances genetic diversity in a population. 

Upper Left A pair of mitotic sister chromatids in a section stained with an antibody to topoisomerase II. Notice that the two chromatids are coiled with opposite helical handedness. Lower Left Meiotic chromosomes of a lily at the pachytene stage in which sister chromatids are connected along their length in a synaptonemal complex. From Kleckner, N. (1996) Proc. Natl. Acad, Sci U.S.A. 93, 8167-8174... 

Mapping of eukaryotic chromosomes has involved additional methods which are discussed in Sections E and G,l. These incluse radiation hybrid mapping,104 use of meiotic recombination, identification of restriction fragment length polymorphisms (RFLPs described in Section E,7), and use of expressed sequence tags (ESTs), short DNA sequences deduced from mRNA molecules transcribed from the DNA.105 106... 

During the prophase of the first meiotic division (meiosis I) two homologous pairs of partially "condensed" chromosomes must find each other and pair with appropriate orientation. A protein in the telomeres of the chromosomes seems to be involved.269 277 The key structure in meiotic crossing-over is the ribbonlike synaptonemal complex formed by the pairs of homologous chroma fids.271/278 2791 This complex, in which a proteinaceous core or axial element separates the greatly extended chromatid pairs (Fig. 26-13), is fully formed in the pachytene stage of meiosis. Formation of the synaptonemal complex is preceded by development of a few double-stranded breaks in... 

Figure 26-13 Synaptonemal complexes. (A) Aligned pairs of homologous chromatids lying 0.4 pm apart in Allium cepa. Arrows indicate "recombination nodules" which may be involved in initiating formation of crossovers. Portions of meiotic chromosomes of lily are shown at successive stages (B) Pachytene. (C) Portion of diplotene nucleus. (D) A bivalent at diplo-tene. (E) Two bivalents at diakinesis. Pairs of sister chromatids are coiled with appropriate handedness. (F) Sister chromatid cores are far apart in preparation for separation. A chiasma is present between the two central strands. (B) through (F) courtesy of Stephen Stack.279,279d (G) Pair of sister chromatids coiled with opposite handedness at metaphase. These are immun-ostained with anti-topoisomerase II antibodies. From Boy de la Tour and Laemmli.280 Courtesy of U. K. Laemmli.

---