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Broad-scale recombination patterns underlying proper disjunction in humans.

ABSTRACT: Although recombination is essential to the successful completion of human meiosis, it remains unclear how tightly the process is regulated and over what scale. To assess the nature and stringency of constraints on human recombination, we examined crossover patterns in transmissions to viable, non-trisomic offspring, using dense genotyping data collected in a large set of pedigrees. Our analysis supports a requirement for one chiasma per chromosome rather than per arm to ensure proper disjunction, with additional chiasmata occurring in proportion to physical length. The requirement is not absolute, however, as chromosome 21 seems to be frequently transmitted properly in the absence of a chiasma in females, a finding that raises the possibility of a back-up mechanism aiding in its correct segregation. We also found a set of double crossovers in surprisingly close proximity, as expected from a second pathway that is not subject to crossover interference. These findings point to multiple mechanisms that shape the distribution of crossovers, influencing proper disjunction in humans.

SUBMITTER: Fledel-Alon A

PROVIDER: S-EPMC2734982 | biostudies-literature | 2009 Sep

REPOSITORIES: biostudies-literature

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Broad-scale recombination patterns underlying proper disjunction in humans.

Fledel-Alon Adi A Wilson Daniel J DJ Broman Karl K Wen Xiaoquan X Ober Carole C Coop Graham G Przeworski Molly M

PLoS genetics 20090918 9

Although recombination is essential to the successful completion of human meiosis, it remains unclear how tightly the process is regulated and over what scale. To assess the nature and stringency of constraints on human recombination, we examined crossover patterns in transmissions to viable, non-trisomic offspring, using dense genotyping data collected in a large set of pedigrees. Our analysis supports a requirement for one chiasma per chromosome rather than per arm to ensure proper disjunction ...[more]

PMID: 19763175

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Project description:BackgroundThere have been numerous studies on dinosaur biogeographic distribution patterns. However, these distribution data have not yet been applied to ecological questions. Ecological studies of dinosaurs have tended to focus on reconstructing individual taxa, usually through comparisons to modern analogs. Fewer studies have sought to determine if the ecological structure of fossil assemblages is preserved and, if so, how dinosaur communities varied. Climate is a major component driving differences between communities. If the ecological structure of a fossil locality is preserved, we expect that dinosaur assemblages from similar environments will share a similar ecological structure.Methodology/principal findingsThis study applies Ecological Structure Analysis (ESA) to a dataset of 100+ dinosaur taxa arranged into twelve composite fossil assemblages from around the world. Each assemblage was assigned a climate zone (biome) based on its location. Dinosaur taxa were placed into ecomorphological categories. The proportion of each category creates an ecological profile for the assemblage, which were compared using cluster and principal components analyses. Assemblages grouped according to biome, with most coming from arid or semi-arid/seasonal climates. Differences between assemblages are tied to the proportion of large high-browsing vs. small ground-foraging herbivores, which separates arid from semi-arid and moister environments, respectively. However, the effects of historical, taphonomic, and other environmental factors are still evident.Conclusions/significanceThis study is the first to show that the general ecological structure of Late Jurassic dinosaur assemblages is preserved at large scales and can be assessed quantitatively. Despite a broad similarity of climatic conditions, a degree of ecological variation is observed between assemblages, from arid to moist. Taxonomic differences between Asia and the other regions demonstrate at least one case of ecosystem convergence. The proportion of different ecomorphs, which reflects the prevailing climatic and environmental conditions present during fossil deposition, may therefore be used to differentiate Late Jurassic dinosaur fossil assemblages. This method is broadly applicable to different taxa and times, allowing one to address questions of evolutionary, biogeographic, and climatic importance.

Project description:UnlabelledRecombination plays a critical role in virus evolution. It helps avoid genetic decline and creates novel phenotypes. This promotes survival, and genome sequencing suggests that recombination has facilitated the evolution of human pathogens, including orthopoxviruses such as variola virus. Recombination can also be used to map genes, but although recombinant poxviruses are easily produced in culture, classical attempts to map the vaccinia virus (VACV) genome this way met with little success. We have sequenced recombinants formed when VACV strains TianTan and Dryvax are crossed under different conditions. These were a single round of growth in coinfected cells, five rounds of sequential passage, or recombinants obtained using leporipoxvirus-mediated DNA reactivation. Our studies showed that recombinants contain a patchwork of DNA, with the number of exchanges increasing with passage. Further passage also selected for TianTan DNA and correlated with increased plaque size. The recombinants produced through a single round of coinfection contain a disproportionate number of short conversion tracks (<1 kbp) and exhibited 1 exchange per 12 kbp, close to the ∼1 per 8 kbp in the literature. One by-product of this study was that rare mutations were also detected; VACV replication produces ∼1×10(-8) mutation per nucleotide copied per cycle of replication and ∼1 large (21 kbp) deletion per 70 rounds of passage. Viruses produced using DNA reactivation appeared no different from recombinants produced using ordinary methods. An attractive feature of this approach is that when it is combined with selection for a particular phenotype, it provides a way of mapping and dissecting more complex virus traits.ImportanceWhen two closely related viruses coinfect the same cell, they can swap genetic information through a process called recombination. Recombination produces new viruses bearing different combinations of genes, and it plays an important role in virus evolution. Poxviruses are a family of viruses that includes variola (or smallpox) virus, and although poxviruses are known to recombine, no one has previously mapped the patterns of DNAs exchanged between viruses. We coinfected cells with two different vaccinia poxviruses, isolated the progeny, and sequenced them. We show that poxvirus recombination is a very accurate process that assembles viruses containing DNA copied from both parents. In a single round of infection, DNA is swapped back and forth ∼18 times per genome to make recombinant viruses that are a mosaic of the two parental DNAs. This mixes many different genes in complex combinations and illustrates how recombination can produce viruses with greatly altered disease potential.

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Broad-scale recombination patterns underlying proper disjunction in humans.

Publications

Broad-scale recombination patterns underlying proper disjunction in humans.

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