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91.
Rutkowska J Badyaev AV 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2008,363(1497):1675-1686
Differences in relative fitness of male and female offspring across ecological and social environments should favour the evolution of sex-determining mechanisms that enable adjustment of brood sex ratio to the context of breeding. Despite the expectation that genetic sex determination should not produce consistent bias in primary sex ratios, extensive and adaptive modifications of offspring sex ratio in relation to social and physiological conditions during reproduction are often documented. Such discordance emphasizes the need for empirical investigation of the proximate mechanisms for modifying primary sex ratios, and suggests epigenetic effects on sex-determining mechanisms as the most likely candidates. Birds, in particular, are thought to have an unusually direct opportunity to modify offspring sex ratio because avian females are heterogametic and because the sex-determining division in avian meiosis occurs prior to ovulation and fertilization. However, despite evidence of strong epigenetic effects on sex determination in pre-ovulatory avian oocytes, the mechanisms behind such effects remain elusive. Our review of molecular and cytological mechanisms of avian meiosis uncovers a multitude of potential targets for selection on biased segregation of sex chromosomes, which may reflect the diversity of mechanisms and levels on which such selection operates in birds. Our findings indicate that pronounced differences between sex chromosomes in size, shape, size of protein bodies, alignment at the meiotic plate, microtubule attachment and epigenetic markings should commonly produce biased segregation of sex chromosomes as the default state, with secondary evolution of compensatory mechanisms necessary to maintain unbiased meiosis. We suggest that it is the epigenetic effects that modify such compensatory mechanisms that enable context-dependent and precise adjustment of primary sex ratio in birds. Furthermore, we highlight the features of avian meiosis that can be influenced by maternal hormones in response to environmental stimuli and may account for the precise and adaptive patterns of offspring sex ratio adjustment observed in some species. 相似文献
92.
93.
Jennifer Grubb M. Scott Brown Douglas K. Bishop 《Journal of visualized experiments : JoVE》2015,(102)
The small size of nuclei of the budding yeast Saccharomyces cerevisiae limits the utility of light microscopy for analysis of the subnuclear distribution of chromatin-bound proteins. Surface spreading of yeast nuclei results in expansion of chromatin without loss of bound proteins. A method for surface spreading balances fixation of DNA bound proteins with detergent treatment. The method demonstrated is slightly modified from that described by Josef Loidl and Franz Klein1,2. The method has been used to characterize the localization of many chromatin-bound proteins at various stages of the mitotic cell cycle, but is especially useful for the study of meiotic chromosome structures such as meiotic recombinosomes and the synaptonemal complex. We also describe a modification that does not require use of Lipsol, a proprietary detergent, which was called for in the original procedure, but no longer commercially available. An immunostaining protocol that is compatible with the chromosome spreading method is also described. 相似文献
94.
The brown algal order Tilopteridales contains three monospecific genera with reduced life histories, Which are assumed to have been derived form ancestors with oogamous reproduction and alternation of generations. The Newfoundland population of Haplospora globosa Kjellman still shows an alternation of gametophytes and sporophytes, but the chromosome Numbers remain equal because of parthenogenesis and apomeiosis, However, DNA fluorometry showed that the DNA level is twice as high in the Sporophytes as in the gametophytes, The DNA variation at constant chromosome numbers is presumably due to endomitosis combined with a law degree of polyteny. A genotypic variant of Haplospora is represented by the population at Helgoland (F.R.G.) where only sporophytes exist, Spores develop into sporophytes instead of gametophytes, and the plants have reduced chromosome number but the same DNA level as the Newfoundland sporophytes 相似文献
95.
Aretuza Sousa Veit Schubert Susanne S. Renner 《The Plant journal : for cell and molecular biology》2021,106(1):133-141
In 1917, sex chromosomes in plants were discovered in a liverwort with hetermorphic U and V chromosomes. Such heteromorphy is unexpected because, unlike the XY chromosomes in diploid-dominant plants, in haploid-dominant plants the female U and the male V chromosomes experience largely symmetrical potential recombination environments. Here we use molecular cytogenetics and super-resolution microscopy to study Frullania dilatata, a liverwort with one male and two female sex chromosomes. We applied a pipeline to Illumina sequences to detect abundant types of repetitive DNA and developed FISH probes to microscopically distinguish the sex chromosomes. We also determined the phenotypic population sex ratio because biased ratios have been reported from other liverworts with heteromorphic sex chromosomes. Populations had male-biased sex ratios. The sex chromosomes are monocentric, and of 14 probes studied (eight satellites, five transposable elements and one plastid region), four resulted in unique signals that differentiated the sex chromosomes from the autosomes and from each other. One FISH probe selectively marked the centromeres of both U chromosomes, so we could prove that during meiosis each U chromosome associates with one of the opposite telomeres of the V chromosome, resulting in a head-to-head trivalent. The similarity of the two U chromosomes to each other in size and in their centromere FISH signal positions points to their origin via a non-disjunction event (aneuploidy), which would fit with the general picture of sex chromosomes rarely crossing-over and being prone to suffer from non-disjunction. 相似文献
96.
97.
Artoni RF Vicari MR Endler AL Cavallaro ZI de Jesus CM de Almeida MC Moreira-Filho O Bertollo LA 《Genetica》2006,127(1-3):277-284
B chromosomes in Prochilodus lineatus, a migratory neotropical fish, were analyzed in a comparative study among populations from the Dourada lagoon (State of Paraná, Brazil) and from Mogi-Guaçu river (State of São Paulo, Brazil). The data on C-banding and fluorescent in situ hybridization with a satellite DNA probe (SATH1), indicate that the small metacentric B chromosome might correspond to an isochromosome. On the other hand, both populations presented a distinct set of B chromosomes, differentiated either by their number and by the presence of variant B types in the population from Mogi-Guaçu river. The present results indicate that the B chromosomes of P. lineatus should have an ancient origin, and have undergone a differential evolutionary pathway among distinct populations. 相似文献
98.
Josh Hough Simone Immler Spencer C. H. Barrett Sarah P. Otto 《Evolution; international journal of organic evolution》2013,67(7):1915-1925
Frequency‐dependent selection should drive dioecious populations toward a 1:1 sex ratio, but biased sex ratios are widespread, especially among plants with sex chromosomes. Here, we develop population genetic models to investigate the relationships between evolutionarily stable sex ratios, haploid selection, and deleterious mutation load. We confirm that when haploid selection acts only on the relative fitness of X‐ and Y‐bearing pollen and the sex ratio is controlled by the maternal genotype, seed sex ratios evolve toward 1:1. When we also consider haploid selection acting on deleterious mutations, however, we find that biased sex ratios can be stably maintained, reflecting a balance between the advantages of purging deleterious mutations via haploid selection, and the disadvantages of haploid selection on the sex ratio. Our results provide a plausible evolutionary explanation for biased sex ratios in dioecious plants, given the extensive gene expression that occurs across plant genomes at the haploid stage. 相似文献
99.
Intergeneric transfer of a partial genome and direct production of monosomic addition plants by microprotoplast fusion 总被引:7,自引:0,他引:7
K. S. Ramulu P. Dijkhuis E. Rutgers J. Blaas F. A. Krens W. H. J. Verbeek C. M. Colijn-Hooymans H. A. Verhoeven 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,92(3-4):316-325
Results are reported on the transfer of single, specific chromosomes carrying kanamycin resistance (KanR) and -glucuronidase (GUS) traits from a transformed donor line of potato (Solanum tuberosum) to a recipient line of the tomato species Lycopersicon peruvianum through microprotoplast fusion. Polyethylene glycol-induced mass fusion between donor potato microprotoplasts containing one or a few chromosomes and normal recipient diploid L. peruvianum protoplasts gave several KanR calli. A high frequency of plants regenerated from KanR calli expressed both KanR and GUS, and contained one or two copies of npt-II and a single copy of gus. Genomic in situ hybridization showed that several microprotoplast hybrid plants had one single potato donor chromosome carrying npt-II and gus genes and the complete chromosome complement of the recipient L. peruvianum (monosomic additions). Several monosomic-addition hybrid plants could be regenerated within the short time of 3 months and they were phenotypically normal, resembling the recipient line. These results suggest that the transfer of single chromosomes is tolerated better than is the transfer of the whole donor genome. The unique advantages of microprotoplast fusion are discussed: these include the direct production of monosomic addition lines for the transfer and introgression of economically important traits in sexually-incongruent species, the construction of chromosome-specific DNA libaries, high-resolution physical mapping and the identification of alien chromosome domains related to gene expression. 相似文献
100.
Staiber W 《Cell and tissue research》2007,329(1):197-203
Additional chromosomes present only in the germ line are a specific feature of the Orthocladiinae, a subfamily of the Chironomidae.
During the complex chromosome cycle in the orthocladiid Acricotopus lucidus, about half of the germ-line-limited chromosomes (Ks) are eliminated in the first division of the primary germ cells. Following
normal gonial mitoses, the reduction in the number of Ks is compensated for, in the last mitosis prior to meiosis, by a monopolar
movement of the unseparated Ks, while the somatic chromosomes (Ss) segregate equally. This differential mitosis produces daughter
cells with different chromosome constitutions and diverse developmental fates. A preferential segregation of mitochondria
occurs to one pole associated with an asymmetric formation of the mitotic spindle. This has been detected in living gonial
cells in both sexes by using MitoTracker probes and fluorochrome-labelled paclitaxel (taxol). In males, the resulting unequal
partitioning of mitochondria to the daughter cells is equalised by the transport of mitochondria through a permanent cytoplasmic
bridge from the aberrant spermatocyte to the primary spermatocyte. This asymmetry in the distribution and in the segregation
of cytoplasmic components in differential gonial mitosis in Acricotopus may be involved in the process of cell-fate determination.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorised users. 相似文献