Análisis de Factores Externos que influyen en los Hedge Funds

More than three billion years ago, the earth was completely different from what we know of it today, sole living organisms at that time developed

∗Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Im Neuenheimer feld 364, 69120 Heidelberg, Germany

†Institute of Pharmacy and Biochemistry, Johannes Gutenberg University, Staudinger Weg 5, 55128 Mainz, Germany

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mechanisms that enabled the evolution of all complex life forms on earth.

They may have started with photosynthesis to generate energy and contin-ued with splitting water molecules, releasing oxygen into the atmosphere that may have been the starting point for the complex, multicellular life.¹ Our earth contains, in addition to plants and microorganisms, a large num-ber of complex animal species, which is estimated between 1 million up to 20 million. Such numbers may sound enormous at first glance, but they might represent only a minor fraction (probably less than 1percent) of ani-mals that have ever existed. During the evolution of life, aniani-mals diverged from a common ancestor more than 540 million years ago through mod-ifications of DNA that led to morphological diversity. Yet, they all share common specific gene families that are responsible for major patterns of body composition. Animal diversity increased dramatically in Cambrium (545–490 million years ago) resulting in the development of some of the modern phyla known today such as arthropods or molluscs, and to the appearance of large, complex animals in the Early-Middle Cambrian — a period called the “Cambrian explosion.” So far, 35 animal phyla have been identified that are grouped according to common shared characteristics.² Although those complex life forms seem to be more attractive, the quasi invisible microbes are by far more abundant and diverse than multicellular taxa. They are “the engine of life” as they maintain the essential atmospheric and chemical conditions through the conversion of carbon, nitrogen, oxy-gen and sulfur into forms accessible to other life forms.¹

To capture the origin and evolution of life, it is necessary to study phylo-genetic relationships among individuals. Based on anatomical and embry-ological comparisons many diverse phylogenetic schemes and trees have been suggested and put into question during the last decades. To circum-vent critical and inconsistent morphological comparisons, genetic charac-ters have been used successfully to determine phylogenies of organisms.²

First, there are only few genes and proteins that are responsible and even essential for the regulation of the development of organisms. These regulation factors are termed “genetic toolkit,” and seem to be present in any given animal. This toolkit mainly consists of transcription factors regu-lating the expression of genes involved in signalling pathways, which medi-ate cell-to-cell interactions involved in formation and composition of the body. Toolkit genes are conserved throughout evolution. An example is

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Hox genes, first identified in Drosophila and later also in frogs, mice and humans (vertebrates). The discovery of the same genetic toolkit in totally different and even long-diverged phyla raises many developmental and evo-lutionary questions, but also allows some insights into the mysteries of life.

How do totally different structures that are controlled by the same genetic toolkit develop and how does this finding influence understanding about phylogenetics and evolution.²

Possible answers may be: Genetic differences may arise from distinct gene expression patterns during different developmental phases; expressed gene products may interact with distinct interaction networks dependent on the time of expression. Moreover, genetic differences result from differ-ent coding contdiffer-ents, including the number and biochemical functions of toolkit genes. The most striking events are mutation, duplication and diver-gence based on DNA replication errors or unequal cross-over events during recombination that lead to sequence development and the formation of gene families. Interestingly, the extent of gene duplication was positively correlated with the complexity of the animal phylum.²

However, in evolution, sequence homology was conserved within and among phlya, as identified for toolkit genes and also for “housekeeping”

genes. Therefore, these sequences must have been present in the ancestor of this group. Consequently, initial gene sequence diverged, leading to many distinct phlya and species.²

In summary, changes in developmental gene regulation are dominant mechanisms leading to different morphological evolution. The degree of divergence was shown to be correlated with the relationship of phyla. Thus, evolutionary conserved gene families enable the construction of phyloge-netic trees based on gephyloge-netic characteristics (e.g. the presence or absence of particular genes or the linkage of a group of genes).²Genetic analysis based on small sub-unit rRNA (SSU rRNA) comparisons lead to the construction of the popular tripartite tree of life created by C.R. Woese and co-workers in the late 1970s. According to this phylogenetic tree, life on earth is divided into three kingdoms,³of Archaea, Bacteria and Eukaryota instead of a main division between plants and animals as proposed by Linnaeus at the begin-ning of the twentieth century or the five-kingdom system suggested by R.H. Whittaker in 1969.⁴Since then, microbiology has followed a constant revolution, and the invention of molecular methods such as amplification,

cloning and sequencing of small subunit ribosomal RNA genes from the environment facilitates access to microbial diversity.³

The greatest phylogenetic diversity can be found in the microbial world, which had about three billion years more to evolve and diversify to reach their recent variety. The huge number of microbes play a key role in main-taining atmospheric and chemical conditions necessary for survival of all life forms on earth. Thus, especially bacterial phyla show an explosive radi-ation. Therefore, they represent the maximal diversity on earth, since they are able to occupy every imaginable niche with the exception of a few extreme environments, such as salt crystallizers or hydrothermal vents that are dominated by archaea. Classical DNA reassociation data together with new analytical approaches estimates several million bacterial species solely present in soil.⁵By contrast, archaea split into two (or perhaps three) king-doms with much more restricted diversity and scaled differentiation, mostly living under extreme energy-challenging conditions. Several attempts were made to explain the evolution of eukaryota, the most famous of which was the archaezoa hypothesis. However, most of the deepest nodes of the eukaryotic tree remain a mystery.²It is important to keep in mind that these ratings are based on findings by conventional laboratorial techniques. The real biodiversity may still not be adequately estimated, and new develop-ments may lead to totally different distributions among kingdoms.

In the context of phylogenetics, it is necessary to introduce the term

“biodiversity” that covers many aspects of biological variation. Biodiversity was defined in 1992 by the Convention on Biological Diversity:⁶

“Biological diversity means the variability among living organisms from all sources including, inter alia (i.e. among other things), terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and ecosystems.”

Thus, biodiversity comprises all forms, levels and combinations of nat-ural variation. A common concept puts forward three categories of biodi-versity: ecological diversity that includes the diversity of biomes, bioregions, landscapes, ecosystems, habitats, niches and populations, organismal diver-sity (domains (or kingdoms), phyla, families, genera, species, subspecies, populations and individuals), and genetic diversity that comprises vari-ations in populvari-ations, individuals, chromosomes, genes and nucleotides.

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These groups can be considered separately, but share common elements as well, such as “populations” that appears in all three categories. Therefore, it is difficult to find exact definitions with precise demarcations of all levels of biodiversity and going further into detail is beyond the scope of this overview.⁶

Most genetic studies focus on microorganisms because they show the greatest diversity on earth. Genetic analyses are necessary to study tax-onomy, evolution, physiology and ecology of microbes.⁷One can get an insight into the huge microbial biodiversity, by the in vitro cultivation of microbes. The most challenging problem is that most microorganisms are difficult to capture for cultivation due to specialized growth requirements.

Thus, we are not aware of their existence.^8,9Accordingly, only a minority of microorganisms living in a given habitat are cultivable. For example, only 0.001–0.1 percent of the microorganisms in seawater, 0.25 percent in fresh water, 0.25 percent in sediments and 0.3 percent in soil can be grown in culture. Conversely, 99 percent of the microbial diversity are not accessible to classical cultivation methods.^9,10

The first analysis of uncultured bacteria in the environment focused on the construction of a 5S rRNA cDNA library derived from the symbiotic microbial community within the tubeworm Riftia pachyptila.^11,12 Direct cloning of DNA from an environment was initially suggested by Pace et al.¹³ and first applied by Schmidt and co-workers,¹⁴who constructed a λ phage library from a seawater sample to screen for 16S rRNA genes. Since then, viral communities had been the subject of several metagenomic investiga-tions and were among the earliest to be studied, since they play a key role in microbial evolution and ecology.¹²

The increased interest and activity in metagenomic research during the past decade, accompanied by the rapid progress in technology paved the way for the study of single genes, pathways, organisms and even whole commu-nities of many habitats and improved our knowledge of global diversity.¹²