Impronta genómica: la genética desconocida

El nacimiento de la Genética como ciencia se debió a la publicación de los trabajos de Mendel y, fundamentalmente, al redescubrimiento de sus leyes a principios del siglo XX, cuando los científicos De Vries, Correns y Tschermak llegaron a las mismas conclusiones que Mendel en 1865. Durante este siglo de vida, el concepto de herencia como transmisión de genes de una generación a la siguiente, con igual efecto a partir de cada parental, se ha venido aplicando a multitud de genes en todos los grupos de seres vivos, hasta el punto de que la Genética ha emergido como uno de los temas centrales de la Biología actual. Distintos autores, sin embargo, consideran que Mendel seleccionó cuidadosamente un grupo de caracteres en guisantes que segregaban limpiamente, mientras hay muchos otros caracteres en guisantes y en muchas otras especies que no muestran herencia mendeliana. Uno de los cambios importantes de la Genética contemporánea es explicar los caracteres y condiciones que no siguen a Mendel, así como conocer el funcionamiento de mecanismos moleculares de expresión y regulación de genes, descubiertos en las últimas décadas, entre los que se incluyen la edición del ARN y la impronta genómica. Desde este punto de vista el concepto de impronta genómica ha adquirido importancia creciente, porque puede proporcionar una explicación para un conjunto de observaciones notablemente diversas en cuanto a transmisión genética y expresión que no se ajustan a las predicciones de genes estrictamente mendelianos

Evolutionary Dynamics of Multigene Families in Triportheus (Characiformes, Triportheidae): A Transposon Mediated Mechanism?

Triportheus (Characiformes, Triportheidae) is a freshwater fish genus with 18 valid species. These fishes are widely distributed in the major river drainages of South America, having commercial importance in the fishing market, mainly in the Amazon basin. This genus has diverged recently in a complex process of speciation carried out in different river basins. The use of repetitive sequences is suitable to trace the genomic reorganizations occured along the speciation process. In this work, the 5S rDNA multigene family has been characterized at molecular and phylogenetic level. The results showed that other multigene family has been found within the non-transcribed spacer (NTS): the U1 snRNA gene. Double-FISH with 5S and U1 probes were also performed, confirming the close linkage between these two multigene families. Moreover, evidences of different transposable elements (TE) were detected within the spacer, thus suggesting a transposon-mediated mechanism of 5S-U1 evolutionary pathway in this genus. Phylogenetic analysis demonstrated a species-specific grouping, except for Triportheus pantanensis, Triportheus aff. rotundatus and Triportheus trifurcatus. The evolutionary model of the 5S rDNA in Triportheus species has been discussed. In addition, the results suggest new clues for the speciation and evolutionary trend in these species, which could be suitable to use in other Characiformes species

Cytogenomics Unveil Possible Transposable Elements Driving Rearrangements in Chromosomes 2 and 4 of Solea senegalensis

Cytogenomics, the integration of cytogenetic and genomic data, has been used here to reconstruct the evolution of chromosomes 2 and 4 of Solea senegalensis. S. senegalensis is a flat fish with a karyotype comprising 2n = 42 chromosomes: 6 metacentric + 4 submetacentric + 8 subtelocentric + 24 telocentric. The Fluorescence in situ Hybridization with Bacterial Artificial Chromosomes (FISH-BAC) technique was applied to locate BACs in these chromosomes (11 and 10 BACs in chromosomes 2 and 4, respectively) and to generate integrated maps. Synteny analysis, taking eight reference fish species (Cynoglossus semilaevis, Scophthalmus maximus, Sparus aurata, Gasterosteus aculeatus, Xiphophorus maculatus, Oryzias latipes, Danio rerio, and Lepisosteus oculatus) for comparison, showed that the BACs of these two chromosomes of S. senegalensis were mainly distributed in two principal chromosomes in the reference species. Transposable Elements (TE) analysis showed significant differences between the two chromosomes, in terms of number of loci per Mb and coverage, and the class of TE (I or II) present. Analysis of TE divergence in chromosomes 2 and 4 compared to their syntenic regions in four reference fish species (C. semilaevis, S. maximus, O. latipes, and D. rerio) revealed differences in their age of activity compared with those species but less notable differences between the two chromosomes. Differences were also observed in peaks of divergence and coverage of TE families for all reference species even in those close to S. senegalensis, like S. maximus and C. semilaevis. Considered together, chromosomes 2 and 4 have evolved by Robertsonian fusions, pericentric inversions, and other chromosomal rearrangements mediated by TEs

A Comprehensive Integrated Genetic Map of the Complete Karyotype of Solea senegalensis (Kaup 1858)

Solea senegalensis aquaculture production has experienced a great increase in the last decade and, consequently, the genome knowledge of the species is gaining attention. In this sense, obtaining a high-density genome mapping of the species could offer clues to the aquaculture improvement in those aspects not resolved so far. In the present article, a review and new processed data have allowed to obtain a high-density BAC-based cytogenetic map of S. senegalensis beside the analysis of the sequences of such BAC clones to achieve integrative data. A total of 93 BAC clones were used to localize the chromosome complement of the species and 588 genes were annotated, thus almost reaching the 2.5% of the S. senegalensis genome sequences. As a result, important data about its genome organization and evolution were obtained, such as the lesser gene density of the large metacentric pair compared with the other metacentric chromosomes, which supports the theory of a sex proto-chromosome pair. In addition, chromosomes with a high number of linked genes that are conserved, even in distant species, were detected. This kind of result widens the knowledge of this species' chromosome dynamics and evolution

A chromosome-level genome assembly enables the identification of the follicule stimulating hormone receptor as the master sex-determining gene in the flatfish Solea senegalensis

Sex determination (SD) shows huge variation among fish and a high evolutionary rate, as illustrated by the Pleuronectiformes (flatfishes). This order is characterized by its adaptation to demersal life, compact genomes and diversity of SD mechanisms. Here, we assembled the Solea senegalensis genome, a flatfish of great commercial value, into 82 contigs (614 Mb) combining long- and short-read sequencing, which were next scaffolded using a highly dense genetic map (28,838 markers, 21 linkage groups), representing 98.9% of the assembly. Further, we established the correspondence between the assembly and the 21 chromosomes by using BAC-FISH. Whole genome resequencing of six males and six females enabled the identification of 41 single nucleotide polymorphism variants in the follicle stimulating hormone receptor (fshr) consistent with an XX/XY SD system. The observed sex association was validated in a broader independent sample, providing a novel molecular sexing tool. The fshr gene displayed differential expression between male and female gonads from 86 days post-fertilization, when the gonad is still an undifferentiated primordium, concomitant with the activation of amh and cyp19a1a, testis and ovary marker genes, respectively, in males and females. The Y-linked fshr allele, which included 24 nonsynonymous variants and showed a highly divergent 3D protein structure, was overexpressed in males compared to the X-linked allele at all stages of gonadal differentiation. We hypothesize a mechanism hampering the action of the follicle stimulating hormone driving the undifferentiated gonad toward testisEuropean Union's Horizon 2020 research and innovation programme under grant agreement (AQUA-FAANG). Grant Number: 81792. Junta de Andalucía-FEDER Grant. Grant Number: P20-00938. Spanish Ministry of Economy and Competitiveness, FEDER Grants. Grant Numbers: RTI2018-096847-B-C21, RTI2018-096847-B-C22S

Video-Tutorial de la base de datos “Grape Genome Browser”

En este video-tutorial se puede aprender a manejar la base de datos de internet donde está depositada la secuencia del genoma de la vid y acceder e interpretar los resultados de las búsquedas así como la integración con otras bases de datos.El video tutorial explica cómo manejar, interpretar y buscar genes y secuencias de ADN en la base de datos on-line del genoma de la vid llamada “Grape Genome Browser”

Crucigrama de conceptos generales de Genética. Nivel semi-avanzado.

El archivo es un ejercicio desarrollado con JCross en Hotpotatoes para que los alumnos prueben e identifiquen su nivel con respecto a cuestiones de Genética, conceptos, técnicas, características del ADN, etc. El ejercicio permite obtener pistas para completar el crucigrama y de esta manera finalizar el mismo habiendo asimilado o aprendido conceptos ya sabidos o nuevos de Genética. El crucigrama contiene cerca de 40 definiciones de Genética.En este crucigrama aparecen definidos conceptos de Genética General para que el usuario que lo haga, a la vez que se divierte, aprenda y compruebe su nivel de conocimiento de Genética a nivel semi-avanzado

Crucigrama de conceptos generales de Genética. Nivel básico.

El archivo es un ejercicio desarrollado con JCross en Hotpotatoes para que los alumnos prueben e identifiquen su nivel de base con respecto a cuestiones básicas de Genética, conceptos, técnicas, características del ADN, etc. El ejercicio permite obtener pistas para completar el crucigrama y de esta manera finalizar el mismo habiendo asimilado o aprendido conceptos ya sabidos o nuevos de Genética.En este crucigrama aparecen definidos conceptos de Genética General para que el usuario que lo haga, a la vez que se divierte, aprenda y compruebe su nivel de conocimiento de Genética a nivel básico

Técnica de Hibridación in situ de Fluorescencia (FISH) para la localización de secuencias de ADN sobre cromosomas: animación 3D.

Animación en 3D mostrando de manera esquemática los pasos más importantes llevados a cabo durante la elaboración de la técnica de citogenética molecular de Hibridación in situ de Fluorescencia (FISH). Se muestra el marcaje de las sondas, la desnaturalización de la misma así como la hibridación y la detección inmunicitoquímica de la sonda.Se presenta una animación en 3D de la Técnica de Hibridación in situ de Fluorescencia, para la localización de secuencias y regiones de ADN en cromosomas metafásicos, en el que se muestran los principales pasos de la técnica