Double Aneuploidy of Down Syndrome (Trisomy 21) and Jacobs Syndrome (Trisomy XYY) with Complete Tracheal Rings Deformity: Case Report and Literature Review.

Down syndrome (DS, trisomy 21) with an extra copy of chromosome 21 is one of the most common aneuploidies in humans. Jacobs syndrome or XYY syndrome (trisomy XYY) with an extra copy of sex chromosome Y is a rare sex chromosome trisomy in males. Double aneuploidy (DA) with an extra copy of chromosome 21 and sex chromosome Y is an extremely rare occurrence. Most trisomy 21 results from nondisjunction during maternal oocyte meiosis-I, whereas trisomy XYY is results from nondisjunction during paternal spermatocyte meiosis-I. We present a case of natural conception premature newborn of 30.4 weeks gestational age who had a DS facial phenotype with extensive syndactyly on both hands and feet. Other multisystem congenital anomalies were discovered, including mal-aligned perimembranous ventricular septal defect, bicuspid aortic valve, Dandy-Walker malformation's tetra-ventriculomegaly, and a rare complete tracheal rings deformity (CTRD) with trachea stenosis. Prenatal amniocentesis and postnatal chromosomal karyotyping analysis detected 48, XYY, + 21 nontranslocation trisomy 21, and free-lying Y chromosome without translocation. The existence of DA is rarely reported in literature reviews. In this review, we will discuss the characteristics of DS and Jacobs syndrome as well as the associated multiorgan malformation including the rare lethal CTRD.

B chromosomes of multiple species have intense evolutionary dynamics and accumulated genes related to important biological processes.

BACKGROUND: One of the biggest challenges in chromosome biology is to understand the occurrence and complex genetics of the extra, non-essential karyotype elements, commonly known as supernumerary or B chromosomes (Bs). The non-Mendelian inheritance and non-pairing abilities of B chromosomes make them an interesting model for genomics studies, thus bringing to bear different questions about their genetic composition, evolutionary survival, maintenance and functional role inside the cell. This study uncovers these phenomena in multiple species that we considered as representative organisms of both vertebrate and invertebrate models for B chromosome analysis. RESULTS: We sequenced the genomes of three animal species including two fishes Astyanax mexicanus and Astyanax correntinus, and a grasshopper Abracris flavolineata, each with and without Bs, and identified their B-localized genes and repeat contents. We detected unique sequences occurring exclusively on Bs and discovered various evolutionary patterns of genomic rearrangements associated to Bs. In situ hybridization and quantitative polymerase chain reactions further validated our genomic approach confirming detection of sequences on Bs. The functional annotation of B sequences showed that the B chromosome comprises regions of gene fragments, novel genes, and intact genes, which encode a diverse set of functions related to important biological processes such as metabolism, morphogenesis, reproduction, transposition, recombination, cell cycle and chromosomes functions which might be important for their evolutionary success. CONCLUSIONS: This study reveals the genomic structure, composition and function of Bs, which provide new insights for theories of B chromosome evolution. The selfish behavior of Bs seems to be favored by gained genes/sequences.

First Record of a B Chromosome in Polybia fastidiosuscula Saussure (Vespidae) and Investigation of Chromatin Composition Through Microsatellite Mapping.

The characterization of karyotypes is an important aspect in understanding the structure and evolution of genomes. Polybia is a genus of social wasps of the family Vespidae. This genus has 58 species, but for only 8 of these chromosome number and morphology have been reported in the literature. The aim of this study was to describe and characterize the Polybia fastidiosuscula Saussure karyotype, presenting the first case of a B chromosome in Vespidae. In addition, we investigated the chromatin composition of this species through C-banding, base-specific fluorochrome staining, and physical mapping of 7 microsatellites and 18S rDNA. Four colonies of P. fastidiosuscula from Minas Gerais and Paraná states, Brazil, were analyzed. The chromosome number identified was 2n = 34, and 2 colonies presented a B chromosome. We characterized the chromatin composition of this species, analyzing the existence of different microsatellite-rich heterochromatic regions which are also enriched with AT or GC base pairs. We suggest an intraspecific origin of the B chromosome based on the homology of the heterochromatic composition with A chromosomes and also verify that the TTAGG and TCAGG sequences are not telomeric, but only microsatellites that occur in the centromeres of most chromosomes, as well as GAG and CGG.

De novo genome assembly of the cichlid fish Astatotilapia latifasciata reveals a higher level of genomic polymorphism and genes related to B chromosomes.

Supernumerary B chromosomes (Bs) are accessory elements to the regular chromosome set (As) and have been observed in a huge diversity of eukaryotic species. Although extensively investigated, the biological significance of Bs remains enigmatic. Here, we present de novo genome assemblies for the cichlid fish Astatotilapia latifasciata, a well-known model to study Bs. High coverage data with Illumina sequencing was obtained for males and females with 0B (B-), 1B, and 2B (B+) chromosomes to provide information regarding the diversity among these genomes. The draft assemblies comprised 771 Mb for the B- genome and 781 Mb for the B+ genome. Comparative analysis of the B+ and B- assemblies reveals syntenic discontinuity, duplicated blocks and several insertions, deletions, and inversions indicative of rearrangements in the B+ genome. Hundreds of transposable elements and 1546 protein coding sequences were annotated in the duplicated B+ regions. Our work contributes a list of thousands of genes harbored on the B chromosome, with functions in several biological processes, including the cell cycle.