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Browsing by Subject "hybridization"

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  • Distribution of Nonhematopoietic Bull-Dereved Cells in Freemartin Tissues 
    Ilmonen, Lotta (University of HelsinkiHelsingin yliopistoHelsingfors universitet, 2003)
    Stamceller definieras ofta enligt det organ de befinner sig i. Det antas att stamceller från ett visst organ kan ge upphov till alla celler av detta organ och bara till dessa celler. Därför har färska forskningar väckt uppmärksamhet då de påvisat att stamceller kan välja otypiska specialiceringslinjer. Experiment har utförts på bestrålade djur. Det har varit oklart vilken betydelse donatorns stamceller har på mottagarens tillväxt i fysiologiska tillstånd. I denna studie har vi använt kimeriska tvillingkalvar i vilkas nonhematopoetiska vävnader donatorns stamceller har spårats. Med tvillingar av olika kön resulterar placentala anastomoser i tidig embryonal utveckling, i en kimerisk, steril kokalv som kallas freemartin. Med hjälp av Y-kromosom riktad in situ hybridisering kan vi spåra donatorns, tjurkalvens celler i mottagarens, freemartin-kalvens vävnader i deras naturliga omgivning. Hematopoetiska celler spårades med att identifiera deras CD45 yt-antigen och kunde därmed, i kombination med in situ hybridiseringen ekskluderas. Vi har hittat nonhematopoetiska celler härstammande från donatorn i vävnader vars ursprung är långt från varandra, så som entodermet och nerv stängen. Nonhematopoetiska celler som härstammar från donatorn var fåtaliga och de var sporadiskt utspridda i vävnaderna. Detta föreslår att de har ringa betydelse i det fysiologiska uppehållet och i utvecklingen av nötkreaturens vävnader.
  • Selection and gene flow in a stable hybrid zone 
    Razumov, Vitali (2022)
    Climatic cycles lead to changes in habitat suitability, which in turn can lead to allopatry, i.e. isolation, between populations. Lack of gene flow between allopatric populations causes them to diverge through accumulation of genetic differences that can create incompatibilities between lineages upon secondary contact in the form of lowered survivability or reproduction rate in hybrids. Incompatible genes act as reproductive barriers and keep lineages isolated by selection against hybrids, while gene flow and recombination work as a counterforce to selection promoting admixture. Reproductive barriers like these are most often found inside hybrid zones and are well demonstrated in nature, but the isolating effect of individual genetic incompatibilities on genome-wide gene flow is still an open question. Here we test if selection counteracting gene flow maintains a narrow hybrid zone between two subspecies of the meadow grasshopper Pseudochorthippus parallelus. We targeted 0,01 % of the 13 GB genome, recovering a 29,1 mean coverage per locus per individual in targeted regions, when mapping against a transcriptome. We find that, for the nuclear markers, the hybrid zone is narrower than expected under a neutral scenario of no selection, suggesting that it is maintained by selection against hybrids. We also find significant isolation by distance, suggesting gene flow across the hybrid zone despite selection against hybrids. Different parts of the genome show significant excess or deficit of heterozygotes, suggesting that selection and gene flow are heterogeneous throughout the genome. Combined, our results show that reproductive isolation between recently diverged lineages can evolve quickly despite gene flow in neutral and positively selected sites.
  • Selection and gene flow in a stable hybrid zone 
    Razumov, Vitali (2022)
    Climatic cycles lead to changes in habitat suitability, which in turn can lead to allopatry, i.e. isolation, between populations. Lack of gene flow between allopatric populations causes them to diverge through accumulation of genetic differences that can create incompatibilities between lineages upon secondary contact in the form of lowered survivability or reproduction rate in hybrids. Incompatible genes act as reproductive barriers and keep lineages isolated by selection against hybrids, while gene flow and recombination work as a counterforce to selection promoting admixture. Reproductive barriers like these are most often found inside hybrid zones and are well demonstrated in nature, but the isolating effect of individual genetic incompatibilities on genome-wide gene flow is still an open question. Here we test if selection counteracting gene flow maintains a narrow hybrid zone between two subspecies of the meadow grasshopper Pseudochorthippus parallelus. We targeted 0,01 % of the 13 GB genome, recovering a 29,1 mean coverage per locus per individual in targeted regions, when mapping against a transcriptome. We find that, for the nuclear markers, the hybrid zone is narrower than expected under a neutral scenario of no selection, suggesting that it is maintained by selection against hybrids. We also find significant isolation by distance, suggesting gene flow across the hybrid zone despite selection against hybrids. Different parts of the genome show significant excess or deficit of heterozygotes, suggesting that selection and gene flow are heterogeneous throughout the genome. Combined, our results show that reproductive isolation between recently diverged lineages can evolve quickly despite gene flow in neutral and positively selected sites.

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