Chromosome Evolution in the Genus Partamona (Apidae: Meliponini), with Comments on B Chromosome Origin.

The genus Partamona includes 33 species of stingless bees, of which 11 were studied cytogenetically. The main goal of this study was to propose a hypothesis about chromosomal evolution in Partamona by combining molecular and cytogenetic data. Cytogenetic analyses were performed on 3 Partamona species. In addition, the molecular phylogeny included mitochondrial sequences of 11 species. Although the diploid number was constant within the genus, 2n = 34, B chromosomes were reported in 7 species. Cytogenetic data showed karyotypic variations related to chromosome morphology and the amount and distribution of heterochromatin and repetitive DNA. The molecular phylogenetic reconstruction corroborated the monophyly of the genus and separated the 2 clades (A and B). This separation was also observed in the cytogenetic data, in which species within each clade shared most of the cytogenetic characteristics. Furthermore, our data suggested that the B chromosome in the genus Partamona likely originated from a common ancestor of the species that have it in clade B and, through interspecific hybridization, it appeared only in Partamona rustica from clade A. Based on the above, Partamona is an interesting genus for further investigations using molecular mapping of B chromosomes as well as for broadening phylogenetic data.

Evolution of B Chromosomes: From Dispensable Parasitic Chromosomes to Essential Genomic Players.

B chromosomes represent additional chromosomes found in many eukaryotic organisms. Their origin is not completely understood but recent genomic studies suggest that they mostly arise through rearrangements and duplications from standard chromosomes. They can occur in single or multiple copies in a cell and are usually present only in a subset of individuals in the population. Because B chromosomes frequently show unstable inheritance, their maintenance in a population is often associated with meiotic drive or other mechanisms that increase the probability of their transmission to the next generation. For all these reasons, B chromosomes have been commonly considered to be nonessential, selfish, parasitic elements. Although it was originally believed that B chromosomes had little or no effect on an organism's biology and fitness, a growing number of studies have shown that B chromosomes can play a significant role in processes such as sex determination, pathogenicity and resistance to pathogens. In some cases, B chromosomes became an essential part of the genome, turning into new sex chromosomes or germline-restricted chromosomes with important roles in the organism's fertility. Here, we review such cases of "cellular domestication" of B chromosomes and show that B chromosomes can be important genomic players with significant evolutionary impact.

The B Chromosomes of Prochilodus lineatus (Teleostei, Characiformes) Are Highly Enriched in Satellite DNAs.

B or supernumerary chromosomes are dispensable elements that are widely present in numerous eukaryotes. Due to their non-recombining nature, there is an evident tendency for repetitive DNA accumulation in these elements. Thus, satellite DNA plays an important role in the evolution and diversification of B chromosomes and can provide clues regarding their origin. The characiform Prochilodus lineatus was one of the first discovered fish species bearing B chromosomes, with all populations analyzed so far showing one to nine micro-B chromosomes and exhibiting at least three morphological variants (Ba, Bsm, and Bm). To date, a single satellite DNA is known to be located on the B chromosomes of this species, but no information regarding the differentiation of the proposed B-types is available. Here, we characterized the satellitome of P. lineatus and mapped 35 satellite DNAs against the chromosomes of P. lineatus, of which six were equally located on all B-types and this indicates a similar genomic content. In addition, we describe, for the first time, an entire population without B chromosomes.

B Chromosomes in Genus Sorghum (Poaceae).

B chromosomes (Bs) are supernumerary dispensable genomic elements that have been reported in several thousand eukaryotic species. Since their discovery, Bs have been subjected to countless studies aiming at the clarification of their origin, composition, and influence on the carriers. Despite these efforts, we still have very limited knowledge of the processes that led to the emergence of Bs, the mechanisms of their transmission, and the effects of Bs on the hosts. In the last decade, sophisticated molecular methods, including next-generation sequencing, have provided powerful tool to help answer some of these questions, but not many species have received much attention yet. In this review, we summarize the currently available information about Bs in the genus Sorghum, which has so far been on the periphery of scientific interest. We present an overview of the occurrence and characteristics of Bs in various Sorghum species, discuss the possible mechanisms involved in their maintenance and elimination, and outline hypotheses of the origin of Bs in this genus.

A genomic glimpse of B chromosomes in cichlids.

BACKGROUND: B chromosomes (Bs) are extra karyotype elements in addition to A chromosomes and are found in all major eukaryotic taxa. Among hundreds of investigated species, cichlid fishes have emerged as an interesting group of model and have contributed to unravel the complex biology of B chromosome. OBJECTIVE: We review the current state of knowledge on B chromosome investigation in cichlid fish and discuss the recent genomic advances over gene and sequences hunting on Bs and their impact on the current concept of B chromosomes. RESULTS: The Bs of cichlids have been under the subject of classical cytogenetics and high scale DNA, RNA and epigenetics analysis and a list of B chromosome genes and functional sequences has been generated. B chromosomes of cichlids are restricted to females in some species and are enriched with genes, relics of genes, transposable elements and sequences transcribing for many significant biological functions. Diverse potentially functional sequences have been described in the B chromosome of cichlids and could influence important biological characteristics as well seems to affect transcription and epigenetic modifications of the whole genome. CONCLUSION: One of the most enigmatic characteristics of Bs in cichlids is their genic content related to cell cycle and chromosome structure, and their influence over sex rates. The relationship of Bs with cell cycle and sex determination looks like to be connected with the drive of the Bs during cell divisions.

First chromosomal analysis in Deinopidae (Araneae) reveals Sex Chromosome System X1X2X3X4, B chromosomes and polymorphism for centric fusion.

Here we present the first cytogentic study concerning Deinopidae and their controversial phylogenetic position. This study karyologically analyzed one population of Deinopis biaculeata Simon, 1906 and five populations of Deinopis plurituberculata Mello-Leitão, 1925. The majority of specimens of D. plurituberculata exhibited 2n♂ = 40 and 2n♀ = 44 telocentric chromosomes (however some of them showed B chromosomes, belongs to Aquidauana and Botucatu population). The Deinopis biaculeata and D. plurituberculata meiosis of males showed 18 autosomal bivalents + X1X2X3X4, n = 22 and n = 18, a rare sex chromosome system (SCS) in spiders. Some individuals of D. plurituberculata from the Campo Grande population exhibited 2n♂ = 39 and 2n♀ = 43, with a metacentric chromosome (heterozygotes for centric fusion). The D. plurituberculata males with the rearrangement exhibit diplotenes with 16 autosomal bivalents + 1 autosomal trivalent + X1X2X3X4 and metaphases II with n = 22 (18 telocentric autosomes + X1X2X3X4), n = 21 (16 telocentric autosomes + a metacentric autosome + X1X2X3X4), n = 18 (18 telocentric autosomes) and n = 17 (16 telocentric autosomes + a metacentric autosome). The Ag-NORs (silver impregnation) are terminally located in a pair, coinciding with secondary constriction, which is the most common configuration for Araneae. The relatively high diploid number in Deinopis corroborates phylogenies that place it in a basal position among Entelegynes, in the UDOH grade (Uloboridae, Deinopidae, Oecobiidae and Hersiliidae). Centric fusion in only one population of D. plurituberculata suggests low dispersion capacity of this species and an absence of homozygotes for fusion suggests their low viability or a need to increase the population sampling of D. plurituberculata exhibiting the rearrangement. B chromosomes were detected in D. plurituberculata, with interpopulacional, intrapopulacional and intraindividual numerical variation, with cells presenting 0 - 3 and 0 - 6 B chromosomes in populations of Aquidauana and Botucatu, respectively.

First chromosomal analysis in Deinopidae (Araneae) reveals sex Chromosome system X1X2X3X4, B chromosomes and polymorphism for centric fusion

Here we present the first cytogentic study concerning Deinopidae and their controversial phylogenetic position. This study karyologically analyzed one population of Deinopis biaculeata Simon, 1906 and five populations of Deinopis plurituberculata Mello-Leitão, 1925. The majority of specimens of D. plurituberculata exhibited 2n♂ = 40 and 2n♀ = 44 telocentric chromosomes (however some of them showed B chromosomes, belongs to Aquidauana and Botucatu population). The Deinopis biaculeata and D. plurituberculata meiosis of males showed 18 autosomal bivalents + X1X2X3X4, n = 22 and n = 18, a rare sex chromosome system (SCS) in spiders. Some individuals of D. plurituberculata from the Campo Grande population exhibited 2n♂ = 39 and 2n♀ = 43, with a metacentric chromosome (heterozygotes for centric fusion). The D. plurituberculata males with the rearrangement exhibit diplotenes with 16 autosomal bivalents + 1 autosomal trivalent + X1X2X3X4 and metaphases II with n = 22 (18 telocentric autosomes + X1X2X3X4), n = 21 (16 telocentric autosomes + a metacentric autosome + X1X2X3X4), n = 18 (18 telocentric autosomes) and n = 17 (16 telocentric autosomes + a metacentric autosome). The Ag-NORs (silver impregnation) are terminally located in a pair, coinciding with secondary constriction, which is the most common configuration for Araneae. The relatively high diploid number in Deinopis corroborates phylogenies that place it in a basal position among Entelegynes, in the UDOH grade (Uloboridae, Deinopidae, Oecobiidae and Hersiliidae). Centric fusion in only one population of D. plurituberculata suggests low dispersion capacity of this species and an absence of homozygotes for fusion suggests their low viability or a need to increase the population sampling of D. plurituberculata exhibiting the rearrangement. B chromosomes were detected in D. plurituberculata, with interpopulacional, intrapopulacional and intraindividual numerical variation, with cells presenting 0 - 3 and 0 - 6 B chromosomes in populations of Aquidauana and Botucatu, respectively.

Differential Expression of Genes Related to Sexual Determination Can Modify the Reproductive Cycle of Astyanax scabripinnis (Characiformes: Characidae) in B Chromosome Carrier Individuals.

The species complex Astyanax scabripinnis is one of the most studied with respect to origin, distribution, and frequency of B chromosomes, and is considered a model organism for evolutionary studies. Research using population inferences about the occurrence and frequency of the B chromosome shows seasonal variation between sexes, which is associated with the presence of this supernumerary element. We hypothesized that the B chromosome could influence the sex ratio of these animals. Based on this assumption, the present work aimed to investigate if differences exist among levels of gene expression with qRT-PCR of the amh (associated with testicular differentiation) and foxl2a (associated with ovarian differentiation) genes between B-carrier and non-B-carrier individuals. The results showed that for the amh gene, the difference in expression between animals with B chromosomes was not accentuated compared to that in animals without this chromosome. Expression of foxl2a in B-carrier females, however, was reduced by 73.56% compared to females that lacked the B chromosome. Males had no difference in expression of the amh and foxl2a genes between carriers and non-carriers of the B chromosome. Results indicate that the presence of B chromosomes is correlated with the differential expression of sex-associated genes. An analysis of these results integrated with data from other studies on the reproductive cycle in the same species reveals that this difference in expression may be expanding the reproductive cycle of the species.

Genetic variability in a population of Astyanax scabripinnis: recent bottleneck and the possible influence of individuals with B chromosomes

Access the genetic variability of endangered and isolated populations has become an important conservation tool. Astyanax scabripinnis is a well-known fish model for genetic studies, forming very isolated populations in headwaters. Besides that, this species frequently presents supernumerary chromosomes, which elevates the interest on genetic studies. Genetic diversity of an Astyanax scabripinnispopulation from the Atlantic Forest (Serra da Mantiqueira region, Brazil) was assessed with microsatellite markers for the first time. Since microsatellite markers are not described for this species, we tested markers described for a related species for transferability to A. scabripinnis. Six polymorphic loci were sufficiently reliable for population genetic analysis. We found that this population passed through a recent bottleneck because of the presence of an excess of heterozygotes, low allelic diversity, heterozygosity excess, and small effective population size. Individuals with and without B chromosomes were previously identified in this population and our study found private alleles in the individuals without B chromosomes. Furthermore, when individuals without B chromosomes were removed from the analysis, the population did not present heterozygosity excess, suggesting that the bottleneck event was driven by individuals with B chromosomes. Our results provide an insight into the value of microsatellite markers as molecular tools and is the first genetic study using molecular data of A. scabripinnis from this area.

First report on B chromosome content in a reptilian species: the case of Anolis carolinensis.

Supernumerary elements of the genome are often called B chromosomes. They usually consist of various autosomal sequences and, because of low selective pressure, are mostly pseudogenized and contain many repeats. There are numerous reports on B chromosomes in mammals, fish, invertebrates, plants, and fungi, but only a few of them have been studied using sequencing techniques. However, reptilian supernumerary chromosomes have been detected only cytogenetically and never sequenced or analyzed at the molecular level. One model squamate species with available genome sequence is Anolis carolinensis. The scope of the present article is to describe the genetic content of A. carolinensis supernumerary chromosomes. In this article, we confirm the presence of B chromosomes in this species by reverse painting and synaptonemal complex analysis. We applied low-pass high-throughput sequencing to analyze flow-sorted B chromosomes. Anole B chromosomes exhibit similar traits to other supernumerary chromosomes from different taxons: they contain two genes related to cell division control (INCENP and SPIRE2), are enriched in specific repeats, and show a high degree of pseudogenization. Therefore, the present study confirms that reptilian B chromosomes resemble supernumerary chromosomes of other taxons.

Genomic Characterization of a B Chromosome in Lake Malawi Cichlid Fishes.

B chromosomes (Bs) were discovered a century ago, and since then, most studies have focused on describing their distribution and abundance using traditional cytogenetics. Only recently have attempts been made to understand their structure and evolution at the level of DNA sequence. Many questions regarding the origin, structure, function, and evolution of B chromosomes remain unanswered. Here, we identify B chromosome sequences from several species of cichlid fish from Lake Malawi by examining the ratios of DNA sequence coverage in individuals with or without B chromosomes. We examined the efficiency of this method, and compared results using both Illumina and PacBio sequence data. The B chromosome sequences detected in 13 individuals from 7 species were compared to assess the rates of sequence replacement. B-specific sequence common to at least 12 of the 13 datasets were identified as the "Core" B chromosome. The location of B sequence homologs throughout the genome provides further support for theories of B chromosome evolution. Finally, we identified genes and gene fragments located on the B chromosome, some of which may regulate the segregation and maintenance of the B chromosome.

B Chromosomes in Populations of Mammals Revisited.

The study of B chromosomes (Bs) started more than a century ago, while their presence in mammals dates since 1965. As the past two decades have seen huge progress in application of molecular techniques, we decided to throw a glance on new data on Bs in mammals and to review them. We listed 85 mammals with Bs that make 1.94% of karyotypically studied species. Contrary to general view, a typical B chromosome in mammals appears both as sub- or metacentric that is the same size as small chromosomes of standard complement. Both karyotypically stable and unstable species possess Bs. The presence of Bs in certain species influences the cell division, the degree of recombination, the development, a number of quantitative characteristics, the host-parasite interactions and their behaviour. There is at least some data on molecular structure of Bs recorded in nearly a quarter of species. Nevertheless, a more detailed molecular composition of Bs presently known for six mammalian species, confirms the presence of protein coding genes, and the transcriptional activity for some of them. Therefore, the idea that Bs are inert is outdated, but the role of Bs is yet to be determined. The maintenance of Bs is obviously not the same for all species, so the current models must be adapted while bearing in mind that Bs are not inactive as it was once thought.

L Chromosome Behaviour and Chromosomal Imprinting in Sciara Coprophila.

The retention of supernumerary chromosomes in the germ-line of Sciara coprophila is part of a highly-intricate pattern of chromosome behaviours that have fascinated cytogeneticists for over 80 years. Germ-line limited (termed L or "limited") chromosomes are cytologically heterochromatic and late-replicating, with more recent studies confirming they possess epigenetic hallmarks characteristic of constitutive heterochromatin. Little is known about their genetic constitution although they have been found to undergo cycles of condensation and de-condensation at different stages of development. Unlike most supernumeraries, the L chromosomes in S. coprophila are thought to be indispensable, although in two closely related species Sciara ocellaris and Sciara reynoldsi the L chromosomes, have been lost during evolution. Here, we review what we know about L chromosomes in Sciara coprophila. We end by discussing how study of the L chromosome condensation cycle has provided insight into the site and timing of both the erasure of parental "imprints" and also the placement of a putative "imprint" that might be carried by the sperm into the egg.

Sequencing of Supernumerary Chromosomes of Red Fox and Raccoon Dog Confirms a Non-Random Gene Acquisition by B Chromosomes.

B chromosomes (Bs) represent a variable addition to the main karyotype in some lineages of animals and plants. Bs accumulate through non-Mendelian inheritance and become widespread in populations. Despite the presence of multiple genes, most Bs lack specific phenotypic effects, although their influence on host genome epigenetic status and gene expression are recorded. Previously, using sequencing of isolated Bs of ruminants and rodents, we demonstrated that Bs originate as segmental duplications of specific genomic regions, and subsequently experience pseudogenization and repeat accumulation. Here, we used a similar approach to characterize Bs of the red fox (Vulpes vulpes L.) and the Chinese raccoon dog (Nyctereutes procyonoides procyonoides Gray). We confirm the previous findings of the KIT gene on Bs of both species, but demostrate an independent origin of Bs in these species, with two reused regions. Comparison of gene ensembles in Bs of canids, ruminants, and rodents once again indicates enrichment with cell-cycle genes, development-related genes, and genes functioning in the neuron synapse. The presence of B-chromosomal copies of genes involved in cell-cycle regulation and tissue differentiation may indicate importance of these genes for B chromosome establishment.

Cestrum strigilatum (Ruiz & Pavón, 1799) B chromosome shares repetitive DNA sequences with A chromosomes of different Cestrum (Linnaeus, 1753) species.

Species of Cestrum (Linnaeus, 1753) have shown large diversity in the accumulation and distribution of repetitive DNA families, and B chromosomes have been described in seven species. Some types of repetitive DNA were identified in A and B chromosomes in species of this plant group, such as AT-rich SSR, 35S and 5S rDNA, C-Giemsa and C-CMA/DAPI bands and retrotransposons. To increase our understanding of the relationships of A and B chromosomes, the B of C. strigilatum Ruiz & Pavón, 1799 was microdissected, amplified and hybridized in situ against chromosomes of this species, and in six other species of this genus. FISH signals were observed in whole the B of C. strigilatum, including stretches of A chromosomes, as well as in some A chromosomes of all tested species. A strong FISH signal was seen adjacent to the 5S rDNA in the proximal region of pair 8 of all species and, due to this, we have searched for 5S rDNA fragments in the microdissected B chromosome. PCR and sequencing data evidenced 5S rDNA deletion along evolutionary pathways of the B of C. strigilatum. Although A and B chromosomes displayed redundancy in the repetitive DNA families in different species, the B of C. strigilatum seemed to differ from those Bs of other Cestrum species by the loss of rDNA fractions. A possible origin of Bs in Cestrum was discussed.

A novel male-specific SET domain-containing gene setdm identified from extra microchromosomes of gibel carp males.

Various genes have been screened on extra chromosomes, but their molecular characterization, expression pattern and biological function are still unclear. Here, we utilized a male-specific sequence of polyploid gibel carp (Carassius gibelio) to identify a novel male-specific SET (Su(var)3-9, Enhancer-of-zeste, Trithorax) domain-containing gene setdm on extra microchromosomes of gibel carp males. And setdm was characterized in molecule and expression aspects, in which its expression was specific to testis, and had relative high transcription during middle/late stages of testis development. Moreover, prominent expression of Setdm in spermatogenic cells was observed in testis through immunofluorescence co-localization analysis. These results suggest that biological function of setdm might be related to testis development and spermatogenesis of gibel carp. Additionally, the homeologous gene setdmf of setdm, was also characterized, and its expression was gonad-specific, in which its expressed product was detected to mainly distribute in gametogenic cells of testis and ovary, and to have dynamic expression pattern similar to that of setdm. Based on the current results, we propose that the novel male-specific setdm on extra microchromosomes might be functional divergence gene of the gonad-specific setdmf. Therefore, these findings will help us to further understand evolutionary fate and functional role of genes on extra microchromosomes.

B chromosomes: from cytogenetics to systems biology.

Though hundreds to thousands of reports have described the distribution of B chromosomes among diverse eukaryote groups, a comprehensive theory of their biological role has not yet clearly emerged. B chromosomes are classically understood as a sea of repetitive DNA sequences that are poor in genes and are maintained by a parasitic-drive mechanism during cell division. Recent developments in high-throughput DNA/RNA analyses have increased the resolution of B chromosome biology beyond those of classical and molecular cytogenetic methods; B chromosomes contain many transcriptionally active sequences, including genes, and can modulate the activity of autosomal genes. Furthermore, the most recent knowledge obtained from omics analyses, which is associated with a systemic view, has demonstrated that B chromosomes can influence cell biology in a complex way, possibly favoring their own maintenance and perpetuation.

Living apart together: crosstalk between the core and supernumerary genomes in a fungal plant pathogen.

BACKGROUND: Eukaryotes display remarkable genome plasticity, which can include supernumerary chromosomes that differ markedly from the core chromosomes. Despite the widespread occurrence of supernumerary chromosomes in fungi, their origin, relation to the core genome and the reason for their divergent characteristics are still largely unknown. The complexity of genome assembly due to the presence of repetitive DNA partially accounts for this. RESULTS: Here we use single-molecule real-time (SMRT) sequencing to assemble the genome of a prominent fungal wheat pathogen, Fusarium poae, including at least one supernumerary chromosome. The core genome contains limited transposable elements (TEs) and no gene duplications, while the supernumerary genome holds up to 25 % TEs and multiple gene duplications. The core genome shows all hallmarks of repeat-induced point mutation (RIP), a defense mechanism against TEs, specific for fungi. The absence of RIP on the supernumerary genome accounts for the differences between the two (sub)genomes, and results in a functional crosstalk between them. The supernumerary genome is a reservoir for TEs that migrate to the core genome, and even large blocks of supernumerary sequence (>200 kb) have recently translocated to the core. Vice versa, the supernumerary genome acts as a refuge for genes that are duplicated from the core genome. CONCLUSIONS: For the first time, a mechanism was determined that explains the differences that exist between the core and supernumerary genome in fungi. Different biology rather than origin was shown to be responsible. A "living apart together" crosstalk exists between the core and supernumerary genome, accelerating chromosomal and organismal evolution.

Microstructural chromosome reorganization in the genus Trichomycterus (Siluriformes: Trichomycteridae)

Trichomycterus is a specious fish genus within Trichomycterinae and displays remarkable karyotype diversity. However, knowledge about their genomic structure and location of repetitive sequence is still limited. In order to better understand the karyotype diversification, we analyzed nine species of Trichomycterus using classical and molecular cytogenetic techniques. Results revealed a conserved diploid chromosome number of 2n=54 chromosomes in all analyzed species, although remarkable differences on the constitutive heterochromatin distribution were observed. In addition, while the 18S rDNA showed a conserved distribution pattern, the 5S rDNA sites showed a quite diverse location considering the analyzed species. Remarkably, both ribosomal genes were co-located in all species, except in T . iheringi , suggesting that co-localization is probably an ancestral condition in Trichomycterus . Finally, three analyzed species showed heterochromatic B chromosomes, reinforcing the intense genomic reorganization occurring in Trichomycterus . Our results showed that chromosomal variations are not restricted to differences in karyotype formula as previously proposed, but also to modifications on the microstructural level of resolution.

Trichomycterus é um especioso gênero dentro de Trichomycterinae e exibe marcante diversidade cariotípica. No entanto, o conhecimento sobre sua estrutura genômica e localização de seqüências repetitivas ainda é restrita. Para um melhor conhecimento sobre a sua diversificação cariotípica, nós analisamos nove especies de Trichomycterus usando técnicas de citogenética clássica e molecular. Os resultados revelaram um conservado número diploide de 2n = 54 cromossomos em todas as espécies analisadas, embora diferentes marcações na distribuição da heterocromatina constitutiva tenham sido observadas. Além disso, enquanto o DNAr 18S mostrou um padrão de distribuição conservado, os sítios de DNAr 5S mostraram uma localização bastante diversa, considerando as espécies analisadas. Ambos os genes ribossomais foram co-localizados em todas as espécies, exceto em T. iheringi , sugerindo que a co-localização é provavelmente uma condição ancestral em Trichomycterus . Finalmente, três espécies analisadas mostraram cromossomos B heterocromáticos, reforçando uma intensa reoganização genômica ocorrendo em Trichomycterus . Nossos resultados mostraram que variações cromossômicas não estão restritas à diferenças na fórmula cariotípica, como proposto anteriormente, mas também às alterações a níveis de resolução estrutural.

Paternal Transmission of Small Supernumerary Marker Chromosome 15 Identified in Prenatal Diagnosis Due to Advanced Maternal Age.

The detection of supernumerary marker chromosomes (SMCs) in prenatal diagnosis is always a challenge. In this study, we report a paternally inherited case of a small SMC(15) that was identified in prenatal diagnosis due to advanced maternal age. A 39-year-old woman underwent amniocentesis at 16 weeks of gestation. A fetal abnormal karyotype - 47,XX,+mar - with one sSMC was detected in all metaphases. Since this sSMC was critical in the parental decision to continue or interrupt this pregnancy, we proceeded to study the fetus and their parents. Cytogenetic and molecular analyses revealed a fetal karyotype 47,XX,+mar pat.ish idic(15)(ql2)(D15Zl++,SNRPN-), in which the sSMC(15) was a paternally inherited inverted duplicated chromosome and did not contain the critical region of Prader-Willi/Angelman syndromes. Moreover, fetal uniparental disomy was excluded. Based on this information and normal obstetric ultrasounds, the parents decided to proceed with the pregnancy and a phenotypically normal girl was born at 39 weeks of gestation. In conclusion, the clinical effects of sSMCs need to be investigated, especially when sSMCs are encountered at prenatal diagnosis. Here, although the paternal sSMC(15) was not associated with an abnormal phenotype, its characterization allows more accurate genetic counseling for the family progeny.