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Homologous Chromosomes (homologous + chromosome)
Selected AbstractsThe relative lengths of individual telomeres are defined in the zygote and strictly maintained during lifeAGING CELL, Issue 3 2004Jesper Graakjaer Summary Previous studies have indicated that average telomere length is partly inherited (Slagboom et al., 1994; Rufer et al., 1999) and that there is an inherited telomere pattern in each cell (Graakjaer et al., 2003); (Londoņo-Vallejo et al., 2001). In this study, we quantify the importance of the initially inherited telomere lengths within cells, in relation to other factors that influence telomere length during life. We have estimated the inheritance by measuring telomere length in monozygotic (MZ) twins using Q-FISH with a telomere specific peptide nucleic acid (PNA)-probe. Homologous chromosomes were identified using subtelomeric polymorphic markers. We found that identical homologous telomeres from two aged MZ twins show significantly less differences in relative telomere length than when comparing the two homologues within one individual. This result means that towards the end of life, individual telomeres retain the characteristic relative length they had at the outset of life and that any length alteration during the lifespan impacts equally on genetically identical homologues. As the result applies across independent individuals, we conclude that, at least in lymphocytes, epigenetic/environmental effects on relative telomere length are relatively minor during life. [source] Mechanism of malsegregations at meiosis: premature centromere separation and precocious division in female Chinese hamsters stimulated with gonadotropic hormonesCONGENITAL ANOMALIES, Issue 3 2000Shin-ichi Sonta ABSTRACT, Using female Chinese hamsters stimulated with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG), we investigated the influence of hormonal stimulation upon meiotic segregation in oocytes. In 1,576 oocytes ovulated spontaneously from 197 non-treated mature females, the number (percentage) of hyperhaploid oocytes with more than 12 (12,14) chromosomes was 16 (1.0%). These cells had no extra single chromatids, but all had extra chromosomes. Single chromatids were seen in 7 (0.4%) cells with a haploid chromosome set. On the other hand, a total of 1,329 and 1,198 second meiotic (MII) oocytes from 64 mature females and 61 immature females stimulated with PMSG and hCG, respectively, were subjected to chromosomal analysis. Single chromatids were seen in 34 (2.6%) and 62 (5.2%) of these oocytes, respectively. Since these chromatids were mostly paired and the sister chromatids existed near each other in many cells, they may have separated from some chromosomes of haploid cells. Compared with the non-treated females, the frequency of cells with single chromatids was significantly greater in oocytes from both mature and immature females stimulated with PMSG and hCG. The number (percentage) of hyperhaploid cells from mature and immature PMSG-hCG-stimulated females, respectively, was 15 (1.1%) and 14 (1.2%), which was not significantly greater than that in non-treated females. Most of these cells had extra whole chromosomes but one oocyte from mature females and one from immature females had an extra single chromatid. These findings indicate that such hormonal stimulation induces premature centromere separation in MII oocytes and precocious division at anaphase I, which can be assumed by the presence of MII cells with extra single chromatids. Considering that no or less hyperhaploid MII oocytes with an extra single chromatid were seen in oocytes from spontaneous ovulation and from artificial ovulation on hormonal stimulation, these findings suggest that the major mechanism of malsegregations at first meiotic (MI) division is not a precocious division but rather, errors such as nondisjunction of homologous chromosomes (dyads). [source] Interaction between Lim15/Dmc1 and the homologue of the large subunit of CAF-1 , a molecular link between recombination and chromatin assembly during meiosisFEBS JOURNAL, Issue 9 2008Satomi Ishii In eukaryotes, meiosis leads to genetically variable gametes through recombination between homologous chromosomes of maternal and paternal origin. Chromatin organization following meiotic recombination is critical to ensure the correct segregation of homologous chromosomes into gametes. However, the mechanism of chromatin organization after meiotic recombination is unknown. In this study we report that the meiosis-specific recombinase Lim15/Dmc1 interacts with the homologue of the largest subunit of chromatin assembly factor 1 (CAF-1) in the basidiomycete Coprinopsis cinerea (Coprinus cinereus). Using C. cinerea LIM15/DMC1 (CcLIM15) as the bait in a yeast two-hybrid screen, we have isolated the C. cinerea homologue of Cac1, the largest subunit of CAF-1 in Saccharomyces cerevisiae, and named it C. cinerea Cac1-like (CcCac1L). Two-hybrid assays confirmed that CcCac1L binds CcLim15 in vivo. ,-Galactosidase assays revealed that the N-terminus of CcCac1L preferentially interacts with CcLim15. Co-immunoprecipitation experiments showed that these proteins also interact in the crude extract of meiotic cells. Furthermore, we demonstrate that, during meiosis, CcCac1L interacts with proliferating cell nuclear antigen (PCNA), a component of the DNA synthesis machinery recently reported as an interacting partner of Lim15/Dmc1. Taken together, these results suggest a novel role of the CAF-1,PCNA complex in meiotic events. We propose that the CAF-1,PCNA complex modulates chromatin assembly following meiotic recombination. [source] Ploidy manipulation using diploid sperm in the loach, Misgurnus anguillicaudatus: a reviewJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2008H. Yoshikawa Summary This paper assesses the present state of the art of ploidy manipulation in the loach, Misgurnus anguillicaudatus (Teleoste: Cobitidae). Diploid sperm can be obtained from natural tetraploid individuals with four sets of homologous chromosomes. Using diploid sperm, various polyploids and androgenetic diploids have been produced. Cryptic clonal lineages are also recognized in wild populations of the loach. They produce unreduced diploid eggs genetically identical to somatic cells of the mother fish and most diploid eggs develop gynogenetically as a member of the clone. However, some eggs develop to triploid and/or diploid-triploid mosaic individuals by incorporation of sperm nucleus. Diploid-triploid mosaic males exclusively generate fertile diploid sperm with clonal genotypes. Such diploid sperm can also be obtained from artificially sex-reversed clonal individuals. Recent population studies suggested that Japanese M. anguillicaudatus might not be a single species, but a complex involving cryptic species, because wild populations exhibited genetic differentiation at interspecific level. This implies possible relationship between atypical reproduction and natural hybridization in the loach. [source] WHAT DO WE KNOW ABOUT CHAROPHYTE (STREPTOPHYTA) LIFE CYCLES?,JOURNAL OF PHYCOLOGY, Issue 5 2010David Haig The charophyte algae are the closest living relatives of land plants. Their life cycles are usually characterized as haploid with zygotic meiosis. This conclusion, however, is based on a small number of observations and on theoretical assumptions about what kinds of life cycle are possible. Little is known about the life cycles of most charophytes, but unusual phenomena have been reported in comparatively well-studied taxa: Spirogyra and Sirogonium are reported to produce diploid gametes with synapsis of homologous chromosomes before fusion of gametic nuclei; Closterium ehrenbergii is reported to undergo chromosome reduction both before and after syngamy; and zygotes of Coleochaete scutata are reported to replicate their DNA to high levels before a series of reduction divisions. All of these phenomena require confirmation, as does the conventional account. [source] Microsporogenesis and meiotic behavior in nine species of the genus PinusJOURNAL OF SYSTEMATICS EVOLUTION, Issue 4 2009Hui-Sheng DENG Abstract The meiotic behavior of 10 taxa (nine species and one variety) of the genus Pinus was investigated using pollen mother cells (PMCs) to reveal the differentiation among karyotypes. Chromosome spreads were prepared by conventional squashing. The meiotic index and the average configuration were higher, whereas the frequency of aberrance (chromosomal bridges, fragments, or micronuclei) was lower, in all 10 taxa compared with other gymnosperms. The meiotic index, average configuration, and frequency of irregularity were found to be uniform among the species. It was shown that the genomes of the Pinus species investigated were highly stable, confirming results of previous mitotic analyses in this genus. However, slight differentiation of homologous chromosomes among genomes was revealed by analysis of meiotic configurations in Pinus nigra var. poiretiana. Quadrivalents were observed in 9.31% of PMCs in this species. This is the first time that quadrivalents have been observed in gymnosperms. [source] Genetic Exchange Within and Between Assemblages of Giardia duodenalisTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 6 2009ERICA LASEK-NESSELQUIST ABSTRACT. Meiotic sex evolved early in the history of eukaryotes. Giardia duodenalis (syn. Giardia lamblia, Giardia intestinalis), a parasitic protist belonging to an early diverging lineage of eukaryotes, shows no cytological or physiological evidence of meiotic or sexual processes. Recent molecular analyses challenge the idea that G. duodenalis is a strictly clonal organism by providing evidence of recombination between homologous chromosomes within one subgroup (Assemblage A) of this species as well as genetic transfer from one subgroup to another (Assemblage A,B). Because recombination is not well documented and because it is not known whether the observed inter-assemblage transfer represents true reciprocal genetic exchange or a non-sexual process, we analyzed genic sequences from all major subgroups (Assemblages A,G) of this species. For all assemblages, we detected molecular signatures consistent with meiotic sex or genetic exchange, including low levels of heterozygosity, as indicated by allelic sequence divergence within isolates, and intra- and inter-assemblage recombination. The identification of recombination between assemblages suggests a shared gene pool and calls into question whether it is appropriate to divide the genetically distinct assemblages of G. duodenalis into a species complex. [source] Detection of unpaired DNA at meiosis results in RNA-mediated silencingBIOESSAYS, Issue 2 2003Michael J. Hynes During meiosis, homologous chromosomes must pair in order to permit recombination and correct chromosome segregation to occur. Two recent papers1,2 show that meiotic pairing is also important for correct gene expression during meiosis. They describe data for the filamentous fungus Neurospora crassa that show that a lack of pairing generated by ectopic integration of genes can result in silencing of genes expressed during meiosis. This can result in aberrant meioses whose defects are specific to the function of the unpaired gene. Furthermore, mutations affecting the silencing mechanism have been selected in a gene encoding a putative RNA-dependent RNA polymerase. This finding indicates the involvement of a meiotic specific post-transcriptional gene silencing mechanism (PTGS) similar to that observed in vegetative cells in N. crassa and other organisms. Finally, this gene product is essential for normal meiosis, suggesting that RNA-dependent processes are fundamental to the sexual cycle. BioEssays 25:99,103, 2003. Š 2003 Wiley Periodicals, Inc. [source] | ||||||||||