domingo, 1 de maio de 2011
ARTIGO RELACIONADO AO PETAR 13
Vale a pena dar uma lida para inspirar a fala sobre evolução nas nossas atividades cavernículas no PETAR. Quem quiser o artigo completo manifeste-se através do mural de comentários desta página, pois o acesso é restrito.
Genetic basis of eye and pigment loss in the cave crustacean, Asellus aquaticus
- aDepartment of Molecular and Cell Biology, Center of Integrative Genomics, and Department of Integrative Biology, University of California, Berkeley, CA 94720-3200; and
- bBiotechnical Faculty, Department of Biology, University of Ljubljana, SI-1000 Ljubljana, Slovenia
- Edited* by Clifford J. Tabin, Harvard Medical School, Boston, MA, and approved February 25, 2011 (received for review September 15, 2010)
Abstract
Understanding the process of evolution is one of the great challenges in biology. Cave animals are one group with immense potential to address the mechanisms of evolutionary change. Amazingly, similar morphological alterations, such as enhancement of sensory systems and the loss of eyes and pigmentation, have evolved multiple times in a diverse assemblage of cave animals. Our goal is to develop an invertebrate model to study cave evolution so that, in combination with a previously established vertebrate cave system, we can address genetic questions concerning evolutionary parallelism and convergence. We chose the isopod crustacean, Asellus aquaticus, and generated a genome-wide linkage map for this species. Our map, composed of 117 markers, of which the majority are associated with genes known to be involved in pigmentation, eye, and appendage development, was used to identify loci of large effect responsible for several pigmentation traits and eye loss. Our study provides support for the prediction that significant morphological change can be mediated through one or a few genes. Surprisingly, we found that within population variability in eye size occurs through multiple mechanisms; eye loss has a different genetic basis than reduced eye size. Similarly, again within a population, the phenotype of albinism can be achieved by two different genetic pathways—either by a recessive genotype at one locus or doubly recessive genotypes at two other loci. Our work shows the potential of Asellus for studying the extremes of parallel and convergent evolution—spanning comparisons within populations to comparisons between vertebrate and arthropod systems.
domingo, 3 de abril de 2011
domingo, 27 de março de 2011
sexta-feira, 18 de março de 2011
FAST FACTS ABOUT RADIATION FROM THE FUKUSHIMA DAIICHI REACTORS
Elevated radiation levels have been detected at and around the stricken nuclear power station in Japan, but the Chernobyl accident remains far more catastrophic
| March 16, 2011 | 11
The Japan Earthquake and TsunamiOn March 11, a powerful, magnitude 9.0 quake hit northeastern Japan, triggering a tsunami with 10-meter-high waves that reached the U.S. west coast. Here's the science behind the disaster »March 11, 2011
Image: WIKIMEDIA COMMONSSince a magnitude 9.0 earthquake rocked Japan and set loose a massive tsunami March 11, the Tokyo Electric Power Co. (TEPCO) has been scrambling to avert a nuclear disaster at its hardest hit plant. The Fukushima Daiichi nuclear power station, home to six nuclear reactors, has witnessedexplosions at three reactors and a fire in a spent-fuel pool at a fourth. At two reactors, unit Nos. 2 and 3, the vessels containing the nuclear material are suspected to be compromised.
A handful of plant workers remain on the site, implementing emergency cooling measures at the stricken, overheating reactors. Radiation levels have fluctuated wildly during the crisis, and the extent to which the workers' health has been endangered may not become apparent for years. But so far, the radiation releases have been limited compared with the 1986 Chernobyl disaster in Ukraine, an explosive event that caused dozens of cases of fatal radiation poisoning among plant workers and that has been implicated in thousands of thyroid cancer diagnoses in the years that followed. (Nuclear fission of uranium fuel produces radioactive iodine, which gathers in the thyroid gland.) As many nuclear experts have noted, the Fukushima reactors are better designed than the failed Chernobyl reactor.
Below are some facts and figures about the radiation hazard posed by the Fukushima breakdown and how it compares with other nuclear accidents in history. Many of the figures are measured in millisieverts, an international unit of radiation dosage. (One sievert is equal to 100 rems, which is a dosage unit of x-ray and gamma-ray radiation exposure; one millisievert is 0.1 rem.)
Radiation dose at the boundary of the Fukushima Daiichi nuclear power station on March 16: 1.9 millisieverts (mSv) per hour
Peak radiation dose measured inside Fukushima Daiichi on March 15:400 mSv per hour
Maximum allowable exposure for U.S. radiation workers: 50 mSv per year
Average exposure of U.S. residents from natural and man-made radiation sources: 6.2 mSv per year
Estimated total exposure at the boundary of the Three Mile Island site in Pennsylvania during the 1979 accident there: one mSv or less
Average total radiation dose to the 114,500 individuals evacuated during the 1986 Chernobyl disaster: 31 mSv
Half-life of iodine 131, a dangerous radioactive isotope released in nuclear accidents: eight days
Half-life of cesium 137, another major radionuclide released in nuclear accidents: 30 years
Decay products of iodine 131 and cesium 137: both emit gamma rays and beta particles (electrons or positrons)
Amount of nuclear fuel in Chernobyl reactor No. 4 that exploded in 1986:190 metric tons
Amount of nuclear fuel and fission by-products released into the atmosphere during Chernobyl disaster: 25 to 57 metric tons
Approximate amount of nuclear fuel in each crippled Fukushima Daiichi reactor: 70 to 100 metric tons
Sources: Japan Atomic Industrial Forum, International Atomic Energy Agency, U.S. Nuclear Regulatory Commission, National Council on Radiation Protection and Measurements, U.S. Environmental Protection Agency, United Nations Scientific Committee on the Effects of Atomic Radiation, National Institute of Standards and Technology, Nuclear Energy Institute
A handful of plant workers remain on the site, implementing emergency cooling measures at the stricken, overheating reactors. Radiation levels have fluctuated wildly during the crisis, and the extent to which the workers' health has been endangered may not become apparent for years. But so far, the radiation releases have been limited compared with the 1986 Chernobyl disaster in Ukraine, an explosive event that caused dozens of cases of fatal radiation poisoning among plant workers and that has been implicated in thousands of thyroid cancer diagnoses in the years that followed. (Nuclear fission of uranium fuel produces radioactive iodine, which gathers in the thyroid gland.) As many nuclear experts have noted, the Fukushima reactors are better designed than the failed Chernobyl reactor.
Below are some facts and figures about the radiation hazard posed by the Fukushima breakdown and how it compares with other nuclear accidents in history. Many of the figures are measured in millisieverts, an international unit of radiation dosage. (One sievert is equal to 100 rems, which is a dosage unit of x-ray and gamma-ray radiation exposure; one millisievert is 0.1 rem.)
Radiation dose at the boundary of the Fukushima Daiichi nuclear power station on March 16: 1.9 millisieverts (mSv) per hour
Peak radiation dose measured inside Fukushima Daiichi on March 15:400 mSv per hour
Maximum allowable exposure for U.S. radiation workers: 50 mSv per year
Average exposure of U.S. residents from natural and man-made radiation sources: 6.2 mSv per year
Estimated total exposure at the boundary of the Three Mile Island site in Pennsylvania during the 1979 accident there: one mSv or less
Average total radiation dose to the 114,500 individuals evacuated during the 1986 Chernobyl disaster: 31 mSv
Half-life of iodine 131, a dangerous radioactive isotope released in nuclear accidents: eight days
Half-life of cesium 137, another major radionuclide released in nuclear accidents: 30 years
Decay products of iodine 131 and cesium 137: both emit gamma rays and beta particles (electrons or positrons)
Amount of nuclear fuel in Chernobyl reactor No. 4 that exploded in 1986:190 metric tons
Amount of nuclear fuel and fission by-products released into the atmosphere during Chernobyl disaster: 25 to 57 metric tons
Approximate amount of nuclear fuel in each crippled Fukushima Daiichi reactor: 70 to 100 metric tons
Sources: Japan Atomic Industrial Forum, International Atomic Energy Agency, U.S. Nuclear Regulatory Commission, National Council on Radiation Protection and Measurements, U.S. Environmental Protection Agency, United Nations Scientific Committee on the Effects of Atomic Radiation, National Institute of Standards and Technology, Nuclear Energy Institute
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