Answer:
Selection is a directional process that leads to an increase or a decrease in the frequency of genes or genotypes. Selection is the process that increases the frequencies of plant resistance alleles in natural ecosystems through coevolution, and it is the process that increases the frequencies of virulence alleles in agricultural ecosystems during boom and bust cycles.
Selection occurs in response to a specific environmental factor. It is a central topic of population and evolutionary biology. The consequence of natural selection on the genetic structure and evolution of organisms is complicated. Natural selection can decrease the genetic variation in populations of organisms by selecting for or against a specific gene or gene combination (leading to directional selection). It can increase the genetic variation in populations by selecting for or against several genes or gene combinations (leading to disruptive selection or balancing selection). Natural selection might lead to speciation through the accumulation of adaptive genetic differences among reproductively isolated populations. Selection can also prevent speciation by homogenizing the population genetic structure across all locations.
Selection in plant pathology is mainly considered in the framework of gene-for-gene coevolution. Plant pathologists often think in terms of Van der Plank and his concept of "stabilizing selection" that would operate against pathogen strains with unnecessary virulence. As we will see shortly, Van der Plank used the wrong term, as he was actually referring to directional selection against unneeded virulence alleles.
There are three main regions of the kidney.
<span>1.Renal cortex - It is the outer region of the kidney which contains the renal corpuscles and the renal tubules (without the loop of Henle). It produces the erythropoietin.</span>
<span>2.Renal medulla - It is the innermost part of the kidney which contains the renal pyramids.</span>
<span>3.Renal pelvis - It is the region that collects urine from the nephrons, thus it contains the place where ureter leaves the kidney.</span>
<span>The most serious consequence of acute pancreatitis resulting from biliary obstruction is the development of circulatory shock.</span>
<span>In rare cases, acute pancreatitis can lead to necrosis of pancreas tissues. Pancreatic enzymes may get into the bloodstream and cause inflammation and damage to other organs which then can lead to shock, respiratory failure, kidney failure and other complications. This is a very serious situation which can be fatal.</span>
Radon and Thoron are the most significant sources of radiation exposure to people living in the United States accounting for 37% of total radiation exposure.
These are nuclides that are produced from the radioactive decay of materials especially in consumer products and through natural processes such as the decay of radium.
