The parallel evolution in amniotes seen through the eye of functional nodal mutations

Introduction In this article the authors describe an evolutionary convergence in mammals, birds, and reptiles, based on genomic data from NCBI. The evolution of different species and lineages is due to mutations that can appear and accumulate in organisms over time. Those mutations need a high functional potential and have to be conserved in time in order to form new species. The conservation of mutations can occur via selection pressure, mutational compensation, and/or by the separation of members from the same species by geological and environmental events. In this comprehensive study, the authors describe, a genomic landscape of the parallel evolution by analysing functional nodal mutations (fNMs) by using different types of DNA (mitochondrial and nucleic), the thermostability of mtDNA encoding RNA genes, and the structural proximity of proteins, using the available 3D structures from PDB database. Functional nodal mutations (fNMs) can be separated in single nodal (fSNMs), recurrent nodal mutations (fRNMs), occured independently in unrelated lineages and recurrent combinations of nodal mutations (fRCNMs) recurred independently along with other nodal mutations in combinations in more than a single lineage. The recurrent ones can be taken in consideration the most when we are talking about the convergent adaptive responses, that means …

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Evolution of Darwin’s finches and their beaks revealed by genome sequencing

Introduction Darwin’s finches from Galapagos and Cocos Island are classic example of young adaptive radiation, entirely intact because none of the species having become extinct as a result of human activity. They have diversified in beak sizes and shapes, feeding habits and diets in adapting to different food resources. Although traditional taxonomy of Darwin’s is based on morphology and has been largely supported by observations of breeding birds finches, in this paper, authors showed the results of whole-genome re-sequencing of 120 individuals representing all of the Darwin’s finch species inhabiting Galapagos archipelago (Fig. 1a) and two close relatives, trying to analyse patterns of intra-and interspecific genome diversity and phylogenetic relationships among the species. Figure 1a. Sample location of Darwin’s finches Summary and comments of the paper The authors analyzed location and phylogeny of Darwin’s finches and found widespread evidence of interspecific gene flow that may have enhanced evolutionary diversification throughout phylogeny. They also reported discovery of a locus with the major effect on beak shape. They generated 10x sequence coverage per individual bird and using 2×100 base-pair (bp) paired-end reads and found evidence of introgression from three sources: ABBA-BABA tests, discrepancies between phylogenetic trees based on autosomal and sex linked …

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Crossovers are associated with mutation and biased gene conversion at recombination hotspots

Meiosis is an important biological process by which combination of various types of the genes called alleles, are segregated and packed in each germ cell waiting to be transferred and expressed in descendants. This combinations of alleles are products of chromosomal crossovers (COs) during meiotic recombination, which increases the genetic diversity of gametes. Recombination may cause local mutagenic effect at crossover sites with recurrent double strand breaks (DSBs) and thus be the source of sequence variation too. SUMMARY OF THE PAPER By sequencing a large number of single sperm DNA molecules, the authors showed that meiosis is an important source of germline mutations and consequently gene variation. They found more de novo mutations in molecules with COs then in molecules without a recombination event by amplifying single CO products, using allele-specific PCR, at two previously identified recombination hotspots (HSI and HSII) from a pool of sperm. The binding site used by the human recombination machinery contains PRDM9 (PR Domain Containing 9), very polymorphic in humans. In order to investigate why sequence diversity positively correlates with high recombination activity regions, the authors sequenced 5,796 COs in total, including both reciprocal recombination products from 6 Caucasian donors. As a control they screened …

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The genetics of monarch butterfly migration and warning colouration

The monarch butterfly (Danaus plexippus) has a large distribution worldwide. It occurs in North, Central, and South America, Caribbean, and it has recently dispersed to other locations, such as Oceania and Africa. Two traits of this butterfly are incredibly intriguing: their annual migration in North America, and their warning coloration. Among the populations spread out around the globe, only the population of North America has a migrant behavior. Monarchs migrate thousands of kilometers from northern United States and southern Canada to overwinter in Mexico. In Spring, they begin mating and flying back to the North. This long annual migration process happens throughout the life time of more than one generation. Regarding their warning coloration, what is intriguing about it is the occurrence of an intense polymorphism in this trait when compared to other butterflies of the same genus. Monarchs and other Danaus butterflies have by default bright orange wings. This bold coloration warns predators about their toxicity. However, in a monarch population from Hawaii, some butterflies have white instead of orange wings. In this paper, authors investigate, through comparative population genomics, the genetic base for such migration and color polymorphisms of the monarch butterfly. The migration of the monarchs By …

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Comparative analysis of regulatory information and circuits across distant species

Development and homeostasis of all organisms is tightly controlled by transcription regulatory factors that are often highly conserved across deep phylogenies. However, it is unclear to what extend the basic components of these networks (e.g. network motifs and structure, binding frequencies, factor interactions) are preserved in distantly related species. Boyle and colleagues try to shed light on this question in a recent study published by nature in August 2014 (doi:10.1038/nature13668). Paper summary The scientists compare genome-wide binding locations of 165 human, 93 worm and 52 fly transcription regulatory factors in different cellular contexts (developmental stages and tissues) to identify the common properties of their underlying networks (data overview shown in Figure 1, taken from original publication). As already described in smaller-scale studies, they see that DNA binding motifs of orthologous regulatory factors remain similar in distantly related species. Furthermore, these orthologous factors are expressed in similar contexts. However, expression of the orthologous targets is only weakly correlated suggesting an extensive re-wiring of regulatory networks across human, worm and fly. Reconstructions of regulatory networks point to a higher number of master-regulators and upward-flowing edges in human when compared to worm and fly. In all three species, the most abundant network motif …

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The evolutionary history of polar bears

The study of the Ursus lineage, including brown bear (Ursus arctos), black bear (Ursus americanus) and polar bear (Ursus maritimus), provides the ability of addressing the subject of adaptation to extreme (salty and glacial) environments in mammals. Moreover, in last few decades, polar bears won public and media attention, being one of the most charismatic species endangered by global warming and Arctic ice melting. To trace history of innovations and determine response to environmental changes in populations of polar bears, two articles published in Science and Proceedings of the National Academy of Sciences in April and June 2012 provide new data and insights to resolve this question. The absence of fossil of polar bears dating before the late Pleistocene (circa 126 000 years ago) and mitochondrial data, suggesting that polar bear were very closely related to a group of brown bear living in Admiralty, Baranof and Chichagof (ABC) islands in Alaska, previously led to believe that polar bears recently emerged from brown bears. The consequences of this hypotheses would be : Polar bear underwent a very rapid and recent (less than 200 ky ago) adaptation to extreme environment (previously not seen in mammals) Brown bear is a paraphyletic taxon, as …

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