Os peixes da classe Chondrichthyes correspondem a um grupo antigo e bem sucedido que tem demonstrado modificações significantes na estrutura esquelética das nadadeiras pares desde o Paleozóico até o presente. Uma análise anatômica criteriosa baseada no esqueleto apendicular de Chondrichthyes foi realizada e levantou novos caracteres esqueléticos com significado filogenético. A estrutura esquelética das nadadeiras é uma ferramenta complementar e importante para a resolução de questões filogenéticas ainda debatidas dentro da classe, como por exemplo, a questão da monofilia dos tubarões e o posicionamento filogenético das raias. No presente estudo 154 espécies foram analisadas visando expor detalhes da organização das cartilagens radiais, basais, e a morfologia das cinturas peitoral e pélvica. Além disso, duas análises filogenéticas foram realizadas baseadas em 105 caracteres propostos a partir dos padrões esqueléticos das nadadeiras pares observados e de informações da literatura. Algumas relações previamente exploradas em trabalhos morfológicos e moleculares prévios foram recuperadas, como a monofilia de muitas ordens de elasmobrânquios, a relação de grupos irmãos entre os Heterodontiformes e Orectolobiformes, a relação de grupos irmãos entre Zanobatus e os Myliobatiformes, além de um maior suporte ao clado recentemente proposto, Rhinopristiformes. Contudo o grupo Hypnosqualea não foi recuperado no presente estudo, ainda que os tubarões tenham sido resolvidos como parafileticos e apresentando uma nova relação de grupos irmãos com os Batoidea. Adicionalmente, novos caracteres relacionados ao esqueleto apendicular foram propostos para os Holocephali, e estes devem ser testados como potenciais sinapomorfias em analises filogenéticas futuras / Fishes of the class Chondrichthyes correspond to an ancient and well-succeeded group that has demonstrated significant modifications in the skeletal structures of the paired fins from the Paleozoic to the present day. A thorough anatomical analysis based on the appendicular skeleton of Chondrichthyes was realized and raised new skeletal characters with phylogenetic implications. The skeletal structure of paired fins is a complementary tool in the resolution of still debated phylogenetic questions within the class, such as the controversy involving the monophyly of sharks and the phylogenetic positioning of rays. In the present study, 154 taxa were analyzed exposing details of the morphology and arrangement of radials, basals and pectoral and pelvic girdles. In addition, two phylogenetic analyses were conducted based on 105 characters proposed from the observed skeletal patterns of paired fins and data from the literature. Some previous relationships explored in morphological and molecular studies were recovered herein, such as the monophyly of several orders of elasmobranchs, the sister-group relationship between Heterodontiformes and Orectolobiformes, the sister group relationship between Zanobatus and Myliobatiformes, besides a greater support to the recently proposed clade Rhinopristiformes. However, the hypnosqualean group was not recovered in the present study, although the sharks were resolved as paraphyletic and presenting a new sister group relationship with the batoids. Additionally, new characters related to the appendicular skeleton were suggested as derived for the Holocephali, but they must be tested as potential synapomorphies in future phylogenetic analysis

<p>  </p> <p>Down syndrome (DS) is caused by the partial or complete trisomy of human chromosome 21 (Hsa21) and can result in skeletal deficits, including lower bone mineral density (BMD) and increased risk of fracture and osteoporosis or osteopenia earlier than the general population. Mouse models of DS have been developed to understand the genetic mechanisms resulting in these phenotypes, but models differ due to the complex genetic nature of DS and differing genome structures between humans and mice. Ts65Dn mice have been a popular model of DS as they contain ~50% of Hsa21 orthologous genes on a freely segregating minichromosome, but there is speculation that the phenotypes are exaggerated by non-Hsa21 orthologous trisomic genes also present. To address this issue, the Ts66Yah mouse model was developed to remove the non-Hsa21 orthologous trisomic genes. In this study, male and female Ts66Yah mouse femurs were evaluated during bone accrual and peak bone mass to investigate structural differences using micro-computed tomography. Additionally, the role of trisomic <em>Dyrk1a</em>, a Hsa21 gene previously linked to bone deficits in Ts65Dn mice, was evaluated through genetic and pharmacological means in Ts66Yah femurs at postnatal day 36. Ts66Yah mice were found to have little or no trabecular deficits at any age evaluated, but sex-dependent cortical deficits were present at all ages investigated. Reducing <em>Dyrk1a</em> copy number in Ts66Yah mice significantly improved cortical deficits but did not return cortical bone to euploid levels. Pharmacological treatment with DYRK1A inhibitor L21 was confounded by multiple variables, making it difficult to draw conclusions about DYRK1A inhibition in this manner. Overall, these results indicate trabecular deficits associated with Ts65Dn mice may be due to the non-Hsa21 orthologous trisomic genes, and more Hsa21 orthologous trisomic genes are necessary to produce trabecular deficits in DS model mice. As more mouse models of DS are developed, multiple models need to be assessed to accurately define DS-associated phenotypes and test potential treatments.</p>