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Search Results: 1 - 10 of 2926 matches for " Sex Chromosomes "
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Revisiting the X-Chromosome Inactivation and Its Impact on Female Longevity  [PDF]
Lilian Chuaire-Noack, Magda Carolina Sánchez-Corredor, María Martínez-Agüero
Advances in Bioscience and Biotechnology (ABB) , 2014, DOI: 10.4236/abb.2014.56067
Abstract:

X-chromosome inactivation is the genetic mechanism by which X-linked gene expression is equalized between the male and female genders of all placental mammal species. Given that the probability of mutant X-linked allele expression decreases as a result of the inactivation, it has been proposed that females have biological advantages relative to males. These advantages have grabbed the attention of the scientific community in recent years and have focused it on this topic and its clinical implications. To shed some new light on this intriguing phenomenon, this article reviews the most relevant molecular events involved in this process. These events include the role of Xist, the selection mechanism for future X-chromosome inactivation, the age-related inactivation skewing, and the relationship between inactivation and the emergence of X-linked diseases, possible treatments, and longevity.

Chromosome mapping of repetitive sequences in Anostomidae species: implications for genomic and sex chromosome evolution
da Silva Edson Louren?o,de Borba Rafael Splendore,Parise-Maltempi Patrícia Pasquali
Molecular Cytogenetics , 2012, DOI: 10.1186/1755-8166-5-45
Abstract: Background Members of the Anostomidae family provide an interesting model system for the study of the influence of repetitive elements on genome composition, mainly because they possess numerous heterochromatic segments and a peculiar system of female heterogamety that is restricted to a few species of the Leporinus genus. The aim of this study was to isolate and identify important new repetitive DNA elements in Anostomidae through restriction enzyme digestion, followed by cloning, characterisation and chromosome mapping of this fragment. To identify repetitive elements in other Leporinus species and expand on studies of repetitive elements in Anostomidae, hybridisation experiments were also performed using previously described probes of LeSpeI repetitive elements. Results The 628-base pair (bp) LeSpeII fragment was hybridised to metaphase cells of L. elongatus individuals as well as those of L. macrocephalus, L. obtusidens, L. striatus, L. lacustris, L. friderici, Schizodon borellii and S. isognathus. In L. elongatus, both male and female cells contained small clusters of LeSpeII repetitive elements dispersed on all of the chromosomes, with enrichment near most of the terminal portions of the chromosomes. In the female sex chromosomes of L. elongatus (Z2,Z2/W1W2), however, this repeated element was absent. In the remaining species, a dispersed pattern of hybridisation was observed on all chromosomes irrespective of whether or not they were sex chromosomes. The repetitive element LeSpeI produced positive hybridisations signals only in L. elongatus, L. macrocephalus and L. obtusidens, i.e., species with differentiated sex chromosomes. In the remaining species, the LeSpeI element did not produce hybridisation signals. Conclusions Results are discussed in terms of the effects of repetitive sequences on the differentiation of the Anostomidae genome, especially with respect to sex chromosome evolution. LeSpeII showed hybridisation patterns typical of Long Interspersed Elements (LINEs). The differential distribution of this element may be linked to sex chromosome differentiation in L. elongatus species. The relationship between sex chromosome specificity and the LeSpeI element is confirmed in the species L. elongatus, L. macrocephalus and L. obtusidens.
Cytogenetics of the Brazilian whiptail lizard Cnemidophorus littoralis (Teiidae) from a restinga area (Barra de Maricá) in Southeastern Brazil
Peccinini-Seale, D.;Rocha, C. F. D.;Almeida, T. M. B.;Araújo, A. F. B.;De Sena, M. A.;
Brazilian Journal of Biology , 2004, DOI: 10.1590/S1519-69842004000400014
Abstract: chromosomes of cnemidophorus littoralis, a new species of teiid lizard recently described, were studied. the animals are from a restinga area in barra de maricá, rj. the karyotype presents a diploid number of 2n = 46 chromosomes and a chromosomal sex determination mechanism of the type xx:xy. nucleolar organizer regions, ag-nors, are at the sixth pair of chromosomes; there is variability of size and number of the ag-stained nucleoli on the 50 interphase nuclei for each specimen analyzed. these nucleoli are related to nor patterns that also demonstrated variability in size and number. this paper presents the first description of the karyotype of cnemidophorus littoralis and of a chromosomal sex determination mechanism of the xx:xy type in the genus cnemidophorus from southeastern brazil.
The Pricopian gene theory of sexuality is just a hypothesis, but good enough to explain the sex determination in fish
Benone P?s?rin
Aquaculture, Aquarium, Conservation & Legislation , 2010,
Abstract: The present paper summarizes the Pricopian theory of sexuality, discussed in the context offishes’ sex determination. On a logical approach and considering the most recent genetic evidencesreported from studies on bacteria, invertebrates, fish, frogs, reptiles, birds, mammals and even humans,one may allready abandon the chromosomal concept of the sex determination (such as the dosage of Zchromosomes). The sex-determining locus is not a true locus, but an agglomeration of loci very seldomseparated by genetic recombination. Moreover, the W chromosome in ZZ-ZW systems and the Y in XXXYsystems are not empty at all, but still carry information
Karyotype characterization of Anastrepha fruit flies (Diptera: Tephritidae)
Selivon, Denise;Perondini, André L.P.;Rocha, Lincoln S.;
Neotropical Entomology , 2005, DOI: 10.1590/S1519-566X2005000200015
Abstract: the study comprises the description of the c-banded mitotic chromosomes of five species of anastrepha, a. amita zucchi, a. turpiniae stone, a. zenildae zucchi, a. grandis (macquart) and a. leptozona hendel , and a reanalysis of the chromosomes of three other species, a. distincta greene, a. obliqua (macquart) and a. sororcula zucchi. the species have a diploid number of 12, while a. leptozona has 2n = 10. heteromorphism of the sex chromosomes is present in all of the species, which have a xy/xx sex chromosome system. a. grandis and a. leptozona have meta and submetacentric autosomes while all of the chromosomes in the other species are acrocentric. the species can be characterized unequivocally by the length and the pattern of blocks of heterochromatin in the sex chromosomes.
Interspecific chromosomal divergences in the genus Characidium (Teleostei: Characiformes: Crenuchidae)
Alves, José Carlos Pansonato;Paiva, Luiz Ricardo de Souza;Oliveira, Claudio;Foresti, Fausto;
Neotropical Ichthyology , 2010, DOI: 10.1590/S1679-62252010000100010
Abstract: karyotypes of seven fish species of the genus characidium, three of them studied for the first time, were characterized using conventional cytogenetic techniques (giemsa staining, ag-nor, and c-banding). all species presented a diploid number of 2n=50, with only metacentric and submetacentric chromosomes, as observed in all characidium species studied. in two species cells with one to three b chromosomes were observed. all species analyzed have a single nor-bearing chromosome pair with morphological differences among them. characidium cf. zebra shows heterochromatic blocks restricted to the pericentromeric regions of all chromosomes denoting the absence of a sex chromosome system. on the other hand, the species characidium lanei, c. pterostictum, c. lauroi, c. oiticicai, c. schubarti, and characidium sp., besides presenting pericentromeric heterochromatic blocks, exhibited large interstitial and/or terminal heterochromatic blocks, and a zz/zw sex chromosome system. the constitutive heterochromatin seems to play a relevant role in the chromosome differentiation process of the studied species, mainly in relation to the sex chromosomes. the geographical isolation of the rivers in which the species were sampled, associated with their way of life restricted to headwaters environments, may have favored the process of fixation of different karyotypes found in each of the analyzed species.
Chromosome complement and meiosis in three species of the Neotropical bug genus Antiteuchus (Heteroptera, Pentatomidae, Discocephalinae)
Lanzone, Cecilia;Souza, Maria José de;
Genetics and Molecular Biology , 2006, DOI: 10.1590/S1415-47572006000100011
Abstract: orcein staining of spermatocytes was used to study the meiotic behavior of holocentric chromosomes in three member of the genus antiteuchus (commonly known as stink bugs). we describe and illustrate the karyotype of antiteuchus mixtus, a. sepulcralis and a. macraspis which were cytogenetically characterized as having a diploid number of 2n = 14 and an xy sex chromosome system showing pre-reductional meiosis for autosomes and post-reductional meiosis for sex chromosomes. these species were also shown to have a long diffuse stage during meiotic prophase i and aberrant harlequin-type meiocytes. the chiasma frequency was also analyzed for two of the three species studied.
Natural triploidy in Leporinus cf. elongatus bearing sex chromosomes
Molina, Wagner Franco;Margarido, Vladimir Pavan;Galetti Jr, Pedro Manoel;
Genetics and Molecular Biology , 2007, DOI: 10.1590/S1415-47572007000400010
Abstract: although several cases of natural triploidy in fish have already been described, spontaneous polyploidy in species with differentiated sex chromosomes are rare. we report the occurrence of a triploid fish (3n = 81) leporinus cf. elongatus, a species characterized by a highly differentiated zz/zw sex chromosome system, from the s?o francisco river. the occurrence of a zzz triploid adult indicates the viability of this chromosome constitution in this fish.
Karyotype and male pre-reductional meiosis of the sharpshooter Tapajosa rubromarginata (Hemiptera: Cicadellidae)
de Bigliardo,Graciela R; Virla,Eduardo Gabriel; Caro,Sara; Murillo Dasso,Santiago;
Revista de Biología Tropical , 2011,
Abstract: cicadellidae in one of the best represented families in the neotropical region, and the tribe proconiini comprises most of the xylem-feeding insects, including the majority of the known vectors of xylem-born phytopathogenic organisms. the cytogenetics of the proconiini remains largely unexplored. we studied males of tapajosa rubromarginata (signoret) collected at el manantial (tucumán, argentina) on native spontaneous vegetation where sorghum halepense predominates. conventional cytogenetic techniques were used in order to describe the karyotype and male meiosis of this sharpshooter. t. rubromarginata has a male karyological formula of 2n=21 and a sex chromosome system xo:xx (♂:♀). the chromosomes do not have a primary constriction, being holokinetic and the meiosis is pre-reductional, showing similar behavior both for autosomes and sex chromosomes during anaphase i. for this stage, chromosomes are parallel to the acromatic spindle with kinetic activities in the telomeres. they segregate reductionally in the anaphase i, and towards the equator during the second division of the meiosis. this is the first contribution to cytogenetic aspects on proconines sharpshooters, particularly on this economic relevant auchenorrhyncha species. rev. biol. trop. 59 (1): 309-314. epub 2011 march 01.
Identification of avian W-linked contigs by short-read sequencing
Nancy Chen, Daniel W Bellott, David C Page, Andrew G Clark
BMC Genomics , 2012, DOI: 10.1186/1471-2164-13-183
Abstract: Using the Illumina Genome Analyzer, we generated sequence reads from a male domestic chicken (ZZ) and mapped them to the existing female (ZW) genome sequence. This method allowed us to identify segments of the female genome that are underrepresented in the male genome and are therefore likely to be female specific. We developed a Bayesian classifier to automate the calling of W-linked contigs and successfully identified more than 60 novel W-specific sequences.Our classifier can be applied to improve heterogametic whole-genome shotgun assemblies of the W or Y chromosome of any organism. This study greatly improves our knowledge of the W chromosome and will enhance future studies of avian sex determination and sex chromosome evolution.
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