The Message Essay Example For Students

The Message Essay Bomb! Your computer has just been shut down! Damn it, this always happens! Said hendrick. Hendrick!! Come here! Said his mother. Mom whenever I check my mail the computer shuts off. Said Hendrick. Well honey, there is nothing I can do. After dinner hendrick went back up to his room. He glanced at the computer and saw that a screen name named jason252, had said hi to him. Hendrick replied back, who is this? The man had said that he lives right near hendrick. Hendrick was not very smart so he told the man to meet him at publix. So hendrick said to his mother, mom I need to buy some food at publix can you drop me off? Sure, said his mother. We will write a custom essay on The Message specifically for you for only $16.38 $13.9/page Order now Hendrick went into publix and remembered that he told the man that he would meet him at the candy section. So hendrick went there and waited for the man to come. After a while the man had walked up to hendrick and said, are you hendrick? Hendrick replied, yes I am hendrick. All of a sudden the man grabbed hendrick and brought him to his car and left. After an hour Hendricks mother came to publix and couldnt find hendrick anywhere. She was so worried, that she called the cops. Some people in publix saw the man take hendrick. The people told the police the description of the car. The police went to search for hendrick. The next day hendrick was on the news. Hendrick was at the mans house and saw his face. He screamed out, mommy!!!! The man slapped hendrick and cursed him out. At 12:00 that night the police found hendrick and his mom was so happy that the police found him. When hendrick got back home he ran to his room and threw his computer to the ground. It broke and he smiled. His mother came in and kissed him. She said, aol is very dangerous and I never want you talking to people you dont know. Hendrick replied, mom, I am very sorry and this will never happen again.

Background information on how the development LASIK The WritePass Journal

Background information on how the development LASIK Introduction Background information on how the development LASIK IntroductionBackground information on how the development LASIKThe way the LASIK has affected peoples’ lives;ConclusionRelated Introduction Over the thousands last years, human has experienced many ways to redress their sight. One of the most significant inventions was an eyeglass which is discovered in 1268 by Roger Bacon. This invention has developed through creation contact lenses (Teagle Optometry, 2007). However, the majority of humans who wear glasses or contact lenses are bothering from it. Therefore, Jose Barraquer discovered LASIK in 1950, which is considered one of the recent technologies in vision correction. LASIK is a Latin word that indicates to create  a thin layer  of the cornea  (black  eye)  and then  using the laser  vision correction (LASIK Portal, 2010). Background information on how the development LASIK Lasik is one of the most important types of eye surgery in advance medical that intended for improving in particular Myopia, Hyperopia and Astigmatism. It was invention by Jose Barraquer at the first time, where he effectuated the first operation     to reduce the  thin  flaps  in the cornea  to change its shape by keratomileusis. By 1981, the Alaximr Laser was been founded which worked on ultraviolet radiation, and it was used at the first time by Rangaswamy Srinivasan to decrease tissue in specific way   through extract layers of thin films without any effects thermal in surrounding area. As a result, he could use this kind of Laser without any side effect compared to different type of Laser which worked in the field of visible radiation. After a number of experiments, the Lasik technique has been improved in 1990 by Ioannis Pallikaris and Lucio Buratto to become more accuracy than keratomileusis. All of these results led Stephen Brint and Stephen Slade to performed s urgery operation in the United States for the first time (Ezine Articles, 2011). With the development of technology, Lasik has become more fast than before and it has been improved to be better (Wikipedia, 2011). The way the LASIK has affected peoples’ lives; . The majority of humans bother from wearing spectacles or contact lenses therefore they want to eliminate them by Lasik. Lasik has many positive effects on humans including that Lasik has ability to accurately correct most layers of Myopia, Hyperopia and Astigmatism. Moreover, its surgery occupies five to ten minutes with painless or very little pain. It is one of the easiest operations because it is operated by computer and does not require any stitches after it.  Ã‚   One of the most important factors of Lasik that most patients are not longer needed corrective glasses. Conclusion

4 questions to ask when negotiating a job offer

4 questions to ask when negotiating a job offer You have a job offer- awesome! Your work is done, right? After all, you’ve made it through the resume pile/interview/second interview gauntlet and emerged as the winner. Not so fast, champ†¦you still have some work to do. The job offer is just the start of the next phase: negotiating. This is your chance to get as much compensation as you can as you prepare to start this new phase of your career. Let’s review the most important questions to ask as you start to negotiate salary and/or benefits with your new employer.1. How are employees reviewed, and how is this tied to salary increases?This question lets you know what you can expect down the line and what you should negotiate up front. If the salary seems low up front and the company is unlikely to budge very much during this first phase, you can start making your plan- and your case- for an increase later on. If raises at this company are tied to good performance reviews, you can go in to the job on day one with t he goal of achieving an â€Å"excellent† (or whatever the metric is), and can talk with your manager to set specific goals so you’ll be in good shape when it comes time to talk about a pay bump.2. Besides the base pay, are any benefits negotiable?This gives you a sense of the playing field. If you can’t negotiate time off, insurance coverage, or other benefits, there’s no point in spending your time and energy on those points. It also lets you push a bit on the salary, if nothing else is up for discussion. Knowing what’s flexible and what’s not will help you target your negotiation.3. What is the fiscal year for this company?This question is a good one to ask because it’ll tell you when your next window for negotiation or a raise will be. If you’re starting at the beginning of a year and the company’s fiscal year starts in January, then you’ll have a straightforward year before an increase. But if you’re st arting in January and their fiscal year ends after the first quarter (April), you’ll be waiting significantly longer than a year for a potential salary increase. That gives you a bit of leverage to say, â€Å"Since it will be more than a year until I’m eligible for a salary review, I’m hoping we can start with a slightly higher initial salary.†4. Can you send me employee benefit costs?The company should be able to send you a one-pager or a packet outlining the basic benefits offered by the company (insurance, vacation time, etc.) and any related employee contributions/costs. Benefits aren’t usually highly negotiable, but you can use this cost information as part of your proposed salary.As you get started with the job offer negotiation process, the most important part is having as much information as possible at your disposal. That way, you can make realistic requests and have a good idea of how far you can push with your negotiation- or when you sh ould retreat and live to negotiate another day.

Staff Training Strategy Essay Example | Topics and Well Written Essays - 500 words

Staff Training Strategy - Essay Example The essay "Staff Training Strategy" talks about the problems of making the employees work as a team by analyzing the strategy of pairing young people with old employees in order to make sure that they learn from each other as Generation Gap plays an important role in determining the relationship of the teams. Gen Yers are found to be attention seeking and more technology-oriented people, whereas older people tend to be technology avert who try to do things manually. A disagreement was caused by an older employee’s reluctance to use the new payroll system. However, in the end, the dispute was resolved, but what we can learn from the situation is that by pairing up older and young people, there are chances of disputes which are more dangerous than the one which occurred over the new technology. Hence, the company should look into its policy of pairing the different employees. The strategy that the company can use to solve this problem is by conducting personality interview. They can assess the personality types and preferences of its different employees and then can make teams of people who seem similarly, All though there will still be some disputes and disagreements, they would not be as grave as the one in the case. The company can also take an initiative of the teaching of teaching new technology to the older staff. This would bridge the gap between the older and younger population in the organization. By becoming more technology aware, the older people in the organization would also be more productive.

The analysis of teaching service Essay Example | Topics and Well Written Essays - 1750 words

The analysis of teaching service - Essay Example but it actually begins with requirement gathering, analysis, design, coding, testing and acceptance (basically what we have also in Agile methodology as well today). I was more involved in requirement gathering and later on testing part of the process. Therefore I can say I was also involved with such project. Before I use one of the projects as an example and describe about the Work System that was used and the elements of it, I wanted to share some of experiences I’ve had with Systems Analysis and Design. First of all I should I figured out that no matter how much a system is a large or small, the theory will always work if we pay attention to them. The standards would work if you know yours system at first and also if you know what the theory is talking about; although all of these need experience as well. Having said that I believe Systems Analysis and Design is one of the most important aspects of any development project. The better the analysis the easier the development and market new products as well as identify and enter new markets with existing and new products. There are a number of considerations I have related to system analysis and design. From an overarching perspective I recognize that the systems process occurs in nearly all environments. In this way I recognize that even psychology and family relationships have been considered in terms of systems elements. Bronfenbrenner (1979, p. 34) established Ecological Systems theory as a pervading mode of examining human relationships in the home and work environment. In these regards I recognize that not only the structure of work environments, but also the individuals interacting within these environments fall within the domain of systems elements. Another major recognition I have had related to system analysis and design is the relation of systematic inputs and their workplace functionality. Indeed, Alter (2006, p. 1) indicated that one of the primary challenges of system analysis and design i s ineffective design of inputs within the system. Dick & Carey (2009) indicated that the single most important factor of whether a systematic training input will be incorporated into the workplace environment is the context of that workplace. Many times in my past experience I have received training in an element that was later not directly relevant or supported in the workplace environment. Upon entering the workplace environment this systematic component was then disregarded because of ineffective structures. Ultimately, then I recognize that one of the most essential elements of systems and systematic design is ensuring that each of the components operate together in a functional and mechanistic way. Part III. For a nonprofit project I was involved in our specific work system was a high school teacher working in public education. Customers While there are not customers in the traditional sense, there are similar components. In this way there are students achieving and receiving t he learning. There are parents interested in their children’s education. There are administrators and state education board members interested in ensuring the education provided reflects well on their professional competency. Finally, there are business organizations concerned with ensuring that there is an educated workforce to choose from. Products and Services The products and service are course specific. In terms of a mathematics classroom it is important that students learn algebraic functions, geometry, and potentially calculus. Additionally, they gain critical thinking and problem solving abilities. In this way the products and services are the education that is provided for the students. This

Heart Condition Case Study

Heart Condition Case Study Samantha O’Shea Course: Healthcare Support Module: Human Growth and Development Introduction I got permission from Ned to do my assignment on him. Some of his information has been changed for confidentiality reasons. Ned is sixty and the oldest of nine children. Ned has heart condition which is hereditary in his family. His mother had an enlarged heart which the never knew till after she died. Both his father and younger sister also have a heart condition. His father died from the heart condition over twenty years ago. She died at the age of forty two years of age, five years after giving birth to Ned’s younger sister. She also had eight of her children at home which included a set of twins. Ned had a heart attack about ten years ago while he was in. He found it hard to breath and pains in his chest but didn’t realise he was taking the heart attack. When he was brought to the hospital there was test done and the discovered that he had suffered a heart attack. Ned had a second one year’s later. Before Ned had the heart attack he an unhealthy diet and a heavy smoker. He worked full time in a hotel but now is only working part time. Ned enjoys working as he gets to meet other people and it keeps him busy. A heart attack is when arteries become blocked or damaged. Plaque builds up in the arteries causing a blood clot. The muscles become damaged or die which cause the heart attack. Symptoms are: Chest pain which is most common. Shortness of breath Upper body pain i.e. jaw, back and arms Weakness Tiredness To diagnose a heart attack is getting an Electrocardiogram (ECG). Can be done in a hospital or you’re local GPs. (Irish Heart Foundation 2015) Physical, Intellectual, Emotional and Social (P.I.E.S) of development during late adulthood Late adulthood is from the age of sixty-five plus. Their development is completed. Physical People in this age group will be going through different physical development caused by aging, their walking be getting slower. In some cases people will get lose some of their fine motor skills such as writing or open a door. Also some people’s ears grow. By 65 a lot of people will have grey hair, wrinkles, their muscles weakening and skin will losing or not as flexible. Also their bones will get weaker. According to Erikson’s, he believes that people in the 65+ age have more health problems when they get older. Examples off health problems such as diabetes, refluxes, heart condition dementia and motor neuron (MN). Intellectual A lot of people will be fully developed. In some cases some people will lose their memory from dementia or their thinking will start to slow down. Some people won’t be quick enough to remember stuff e.g. birthdays. People won’t be quick enough to solve problems. According to Cliff Notes older people will learn work or information a bit slower than other people or even to remember any work. Their memory won’t be as good as a younger person. But believe that they can still learn as much as a younger person. (Cliff Notes 2014) Emotional Some people could be upset because they are losing people around them such as friends and family. They could be upset because they have to retire. They could be used to working and they don’t want to be sitting around doing nothing which could cause a person to become depressed or lonely. Some people could be emotional because of an illness they have or they could be dying According to Kubler – Ross a person has to go through the different stages of dying. There are five different stages which are Denial, Anger Bargaining, Depression and Acceptance. A person will go through a lot of different emotions from an illness or dying and will go through Kubler – Ross theory. (Cliff Notes 2014) Social A lot of people at this age will have a lot of people around them such as family and friends. If they are retire the can spend a lot more time with people by doing activities or even some lunch. Another side of retiring people will become anti social because the fell that they have know one around them, which can cause people to become depressed. According to Erikson’s Integrity VS Despair 65 + a lot of older people recall on their past. They look back at their pride and their dignity. Erikson believes that people in this age category accept death. He then believes that elderly people start isolating themselves from peer groups. They start looking back at their achievements, mistakes and/or missed opportunities. He often believes that people at this age will start isolating themselves from others. Physical, Intellectual, Emotional and Social (P.I.E.S) of development of individual as well as your own personal prejudices, fears and anxieties Ned’s Physical, Intellectual, Emotional and Social (P.I.E.S) didn’t change much throughout his late adulthood from the heart attack Physical Before Ned had his heart attack he lived an unhealthy lifestyle which included unsociable working hours and he was a heavy smoker. He only works part time now. After having the heart attack he became more tired and he wouldn’t be able to do much work. Ned does certain jobs and he can become weak or breathless. Intellectual Ned has his full senses in his age. He has great memory and is able to solve problems. Ned is able to interact with other people. Ned’s intellectual development didn’t change. Emotional Ned is nervous because he is retiring in a few years. He is used to working because he is working since he was fourteen or fifteen so he has been working for over fifty years. After Ned having the heart attack he was upset because he was going through a difficult time but now he is fine. Social Ned has a good social life. He sees his family regularly and also his friends. He enjoys going to occasions such as weddings to have a good time. Also he enjoys going to his sibling’s house for dinner and a chat. He also has a good relationship with some of his work mates They all started in one of the factories in town and then got the job in the hotel. My own personal prejudice, fears and anxieties on Ned’s Hearth Condition. I am worried that Ned will take another heart attack that would affect his development. It could affect him physically by getting weaker and he mightn’t be able to return to work. Intellectual it could affect him by him losing his memory which wouldn’t be good for Ned. Emotionally and socially it could affect him by being depressed by not able to work if he has another heart attack. Ned could become anti sociable and depressed. Variations/Factors affecting the individual at this stage of life Ned at this stage is still working part time and is enjoying it as is working since he was young. Ned’s health doesn’t affect him that much, unless he is doing something that is making his heart over work such as lifting something to heavy or rushing. It could make him tired or breathless. If Ned does something to put straining on his heart it could affect him by having another heart attack. A way he could manage it is by not lifting anything to heavy or eating unhealthy food which will help his heart. He could go for little walks to keep fit. Another thing that could affect Ned is if he over does something like too much exercise, pushing something he can’t. Ned would be putting too much strain on his heart which could leave him breathless, tired or even in hospital. Ned could do some light exercise. When Ned hits retirement his routine will be out because he won’t be working. Ned won’t be able to interact with as many people because he won’t be working and also he is a single man. He won’t have anyone to talk to. Another way is that Ned stops or cuts down on smoking as it affects his health. Recommendations to respond confidently to needs of person I would recommend Ned to start getting involved with age action so that he can get involved with other people. He won’t become isolated or non sociable with other people. He can meet up with people for an hour or two a week for a chat and a cup of tea. I also recommend that Ned gets involved with the day care centre the days he isn’t working. He can interact with other people and also get his dinner there for little as five euro. In the day care centre they provide activities. I recommend he joins the Active Retirement Association Tullamore (T.A.R.A). This is on one day a week for people over the age of 55. The get to go on trips over Ireland, have social gatherings, exercise and creative opportunities. Another organisation Ned could join is the Arden View resource centre. It allows the people to meet up and socialise with other people, go on day trips, and get to do activities. Ned could do any of these organisations that won’t be too stressful or to harmful on his heart. Ned will get to interact with other people and become more sociable. He would enjoy the activities and socialising with other people because he likes talking and getting involved. Also these would help Ned to get used to being in organisations because he will be retiring in the next year or two. If he starts now he will get used to being in organisations and where as if he leaves it to the last minute he mightn’t have the confidence to join. Conclusion From doing this assignment I learnt that Ned’s family heart condition is genetic in his family. His family should be getting themselves checked for heart condition because the could be affected. I also learnt more about a heart disease and what it’s physical and mental affects are on someone. I learnt that it could kill of some of your heart and I learnt more on the signs and symptoms such as the upper body pain. Bibliography Book Creative Training Book 2015 Web sites Cliffs Notes (2014) Development in Late Adulthood [online], Available: http://www.cliffsnotes.com/sciences/psychology/psychology/developmental-psychology-age-13-to-65/development-in-late-adulthood [accessed 30th March 2015] Cliffs Notes (2014) Intelligence and Memory age 65 [online], Available: http://www.cliffsnotes.com/sciences/psychology/development-psychology/physical-cognitive-development-65/intelligence-and-memory-age-65 [accessed 30th March 2015] Irish Heart Foundation (2015) Heart Attack [online], Available: https://www.irishheart.ie/iopen24/heart-attack-t-7_19_61.html [accessed 29th March 2015] 1 5M4339Samantha O’Shea

The Nature of Viruses

Viruses are sub-cellular agents of infection that must utilize the cellular machinery of bacteria, plants or animals in order to reproduce. Composed of a single strand of genetic material (DNA or RNA) encased in a protein capsid, a virus is too small to be seen by standard light microscopy; indeed, most are less than one hundredth the size of a bacterium. Specific proteins on the viral capsid attach to receptors on the host cell; this attachment process is essential to viral infectivity and explains why viruses may only infect the cells of certain species or may only infect certain cells or tissues within a given host species. While the infecting virus triggers an immune response in the host, some are capable of suppressing that response by infecting and killing cells that control immunity (e. g. HIV attacks lymphocytes). In addition, while most infected cells are destroyed by viral replication, some viruses enter a latent phase within cells, reactivating in the future to produce chronic or relapsing infections. Many viruses use specific carriers (known as vectors) such as mosquitoes, ticks, bats and rodents that transmit the virus to a susceptible host while others are spread between individuals via blood contact or through respiratory, intestinal or sexual secretions. Of special concern is the fact that mutations within the viral genome may allow viruses to skip from one host (e. g. birds, swine, monkeys) to another (e. g. humans), unleashing pandemics. Many common human infections are produced by viruses; these include the common cold, influenza, mononucleosis, herpes infections (including shingles), viral hepatitis (A, B, C and others), HIV, viral gastroenteritis, conjunctivitis, viral pneumonia, encephalitis, viral meningitis and viral infections of the heart, including pericarditis and myocarditis. While viruses do not respond to antibiotics, specific antiviral agents may control (though not cure) chronic disease (such as HIV, Hepatitis B and Hepatitis C) or may modify the severity of acute infection (as in influenza and herpes infections). However, in most viral infections, treatment is, for now, purely symptomatic and supportive. On the other hand, vaccines are capable of preventing some viral infections (e. g. herpes simplex, measles, mumps, rubella, varicella, Hepatitis B) or reducing the severity of an acute infection (e. g. influenza). Beyond the acute or chronic illness that they produce, some viral infections (such and Hepatitis C and certain strains of herpes simplex) are known to be precursors of malignancy. Finally, many researchers suspect that viruses play a role in the pathogenesis of chronic illnesses such as multiple sclerosis and autoimmune disorders. ttp://naturesblog. blogspot. com/2013/01/the-nature-of-viruses. html The Nature of Viruses Viruses exist in two different states, the extracellular infectious particle or virion and the intracellular state consisting of viral nucleic acid. The capsid may be a polyhedron or a helix, or a combination of both (in some phages). Viruses are infective micro ¬o rganisms that show several differences from typical microbial cells. 1. Size. The size range of viruses is from about 20 to 300 nm. On the whole, viruses are much smaller than bacteria. Most animal viruses and all plant viruses and phages are invisible under the light microscope. 2. Simple structure. Viruses have very simple structures. The simplest viruses are nucleoprotein particles consisting of genetic material (DNA or RNA) surrounded by a protein capsid. In this respect they differ from typical cells which arc made up) of proteins, carbohydrates, lipids and nuc1eicacids. The more complex viruses contain lipids and carbohydrates in addition to proteins and nucleic acids, e. g. the enveloped viruses 3. Absence of cellular structure. Viruses do not have any cytoplasm, and thus cytoplasmic organelles like mitochondria, Golgi complexes, lysosomes, ribosomes, etc. , are absent. They do not have any limiting cell membrane. They utilize the ribosomes of the host cell for protein synthesis during reproduction. 4. No independent metabolism. Viruses cannot multiply outside a living cell. No virus has been cultivated in a cell-free medium. Viruses do not have an independent metabolism. They are metabo ¬lically inactive outside the host cell because they do not posses enzyme systems and protein synthesis machinery. Viral nucleic acid replicates by utilizing the protein synthesis machinery of the host. It codes for the synthesis of a limited number of viral proteins, including the subunits or capsomeres of the capsid, the tail protein and some enzymes concerned Viruses have only one nucleic acid, either DNA or RNA. Typical cells have both DNA and RNA. Genomes of certain with the synthesis or the release of virions. 5. Nucleic acids. RNA viruses can be transcribed into complementary DNA strands in the infected host cells, e. g. Rous Sarcoma Virus (RSV). Such RNA viruses are therefore also called RNA-DNA viruses. 6. Crystallization. Many of the smaller viruses can be crystallized, and thus behave like chemicals. 7. No growth and division. Viruses do not have the power of growth and division. A fully formed virus does not increase in, size by addition of new molecules. The virus itself cannot divide. Only its genetic material (RNA or DNA) is capable of reproduction and that too only in a host cell. It will thus be seen that viruses do not show all the characteris ¬tics of typical living organisms. They, however, possess two funda ¬mental characteristics of living systems. Firstly, they contain nucleic acid as their genetic material. The nucleic acid contains instructions for the structure and function of the virus. Secondly, they can reproduce themselves, even if only by using the host cells synthesis machinery. Viral genomes The nucleic acid comprising the genome may be single-stranded or double-stranded, & in a linear, circular or segmented configuration. Single-stranded virus genomes may be: †¢ positive (+)sense, i. e. of the same polarity (nucleotide sequence) as mRNA †¢ negative (-)sense Ambisense – a mixture of the two. N/B. Virus genomes range in size from approximately 3,200 nucleotides (nt) to approximately 1. 2 million base pairs Unlike the genomes of all cells, which are composed of DNA, virus genomes may contain their genetic information encoded in either DNA or RNA. Since viruses are obligate intracellular parasites only able to replicate inside the appropriate host cells, the genome must contain information encoded in a form which can be recognized & decoded by the particular type of cell parasitized. Thus, the genetic code employed by the virus must match or at least be recognized by the host organism. Similarly, the control signals which direct the expression of virus genes must be appropriate to the host. Many of the DNA viruses of eukaryotes closely resemble their host cells in terms of the biology of their genomes: Some DNA virus genomes are complexed with cellular histones to form a chromatin-like structure inside the virus particle. http://expertscolumn. com/content/nature-viruses http://www. mcb. uct. ac. za/tutorial/virorig. html Viral evolution Viral evolution is a subfield of evolutionary biology and virology that is specifically concerned with the evolution of viruses. Many viruses, in particular RNA viruses, have short generation times and relatively high mutation rates (on the order of one point mutation or more per genome per round of replication for RNA viruses). This elevated mutation rate, when combined with natural selection, allows viruses to quickly adapt to changes in their host environment. Viral evolution is an important aspect of the epidemiology of viral diseases such as influenza (influenza virus), AIDS (HIV), and hepatitis (e. . HCV). It also causes problems in the development of successful vaccines and antiviral drugs, as resistant mutations often appear within weeks or months after the beginning of the treatment. One of the main theoretical models to study viral evolution is the quasispecies model, as the viral quasispecies. | Origins Viruses are ancient. Studies at the molecular level have revealed relationships between viruses infecting organisms from each of the three domains of life, and viral proteins that pre-date the divergence of life and thus the last universal common ancestor. 1] This indicates that viruses emerged early in the evolution of life and existed before modern cells. [2] There are three classical hypotheses on the origins of viruses: Viruses may have once been small cells that parasitised larger cells (the degeneracy hypothesis[3][4] or reduction hypothesis[5]); some viruses may have evolved from bits of DNA or RNA that â€Å"escaped† from the genes of a larger organism (the vagrancy hypothesis[6] or escape hypothesis); or viruses could have evolved from complex molecules of protein and nucleic acid at the same time as cells first appeared on earth (the virus-first hypothesis). 5] None of these hypotheses was fully accepted: the regressive hypothesis did not explain why even the smallest of cellular parasites do not resemble viruses in any way. The escape hypothesis did not explain the complex capsids and other structures on virus particles. The virus-first hypothesis was quickly dismissed because it contravened the definition of viruses, in that they require host cells. [5] Virologists are, however, beginning to reconsider and re-evaluate all three hypotheses. [7][8] http://en. wikipedia. org/wiki/Viral_evolution Evolution Time-line of paleoviruses in the human lineage[9] Viruses do not form fossils in the traditional sense, because they are much smaller than the grains of sedimentary rocks that fossilize plants and animals. However, the genomes of many organism contain endogenous viral elements (EVEs). These DNA sequences are the remnants of ancient virus genes and genomes that ancestrally ‘invaded' the host germline. For example, the genomes of most vertebrate species contain hundreds to thousands of sequences derived from ancient retroviruses. These sequences are a valuable source of retrospective evidence about the evolutionary history of viruses, and have given birth to the science of paleovirology. 9] The evolutionary history of viruses can to some extent be inferred from analysis of contemporary viral genomes. The mutation rates for many viruses have been measured, and application of a molecular clock allows dates of divergence to be inferred. [10] Viruses evolve through changes in their DNA (or RNA), some quite rapidly, and the best adapted mutants quickly outnumber their less fit counterparts. In this sense their evolution is Darwinian, just like that of their host organisms. [11] The way viruses reproduce in their host cells makes them particularly susceptible to the genetic changes that help to drive their evolution. 12] The RNA viruses are especially prone to mutations. [13] In host cells there are mechanisms for correcting mistakes when DNA replicates and these kick in whenever cells divide. [13] These important mechanisms prevent potentially lethal mutations from being passed on to offspring. But these mechanisms do not work for RNA and when an RNA virus replicates in its host cell, changes in their genes are occasionally introduced in error, some of which are lethal. One virus part icle can produce millions of progeny viruses in just one cycle of replication, therefore the production of a few â€Å"dud† viruses is not a problem. Most mutations are â€Å"silent† and do not result in any obvious changes to the progeny viruses, but others confer advantages that increase the fitness of the viruses in the environment. These could be changes to the virus particles that disguise them so they are not identified by the cells of the immune system or changes that make antiviral drugs less effective. Both of these changes occur frequently with HIV. [14] Phylogenetic tree showing the relationships of morbilliviruses of different species[15] Many viruses (for example, influenza A virus) can â€Å"shuffle† their genes with other viruses when two similar strains infect the same cell. This phenomenon is called genetic shift, and is often the cause of new and more virulent strains appearing. Other viruses change more slowly as mutations in their genes gradually accumulate over time, a process known as genetic drift. [16] Through these mechanisms new viruses are constantly emerging and present a continuing challenge to attempts to control the diseases they cause. [17][18] Most species of viruses are now known to have common ancestors, and although the â€Å"virus first† hypothesis has yet to gain full acceptance, there is little doubt that the thousands of species of modern viruses have evolved from less numerous ancient ones. 19] The morbilliviruses, for example, are a group of closely related, but distinct viruses that infect a broad range of animals. The group includes measles virus, which infects humans and primates; canine distemper virus, which infects many animals including dogs, cats, bears, weasels and hyaenas; rinderpest, which infects cattle and buffalo; and other viruses of seals, porpoises and dolphins. 20] Although it not possible to prove which of these rapidly evolving viruses is the earliest, for such a closely related group of viruses to be found in such diverse hosts suggests a possible ancient common ancestor. [21] The Nature of Viruses Viruses are sub-cellular agents of infection that must utilize the cellular machinery of bacteria, plants or animals in order to reproduce. Composed of a single strand of genetic material (DNA or RNA) encased in a protein capsid, a virus is too small to be seen by standard light microscopy; indeed, most are less than one hundredth the size of a bacterium. Specific proteins on the viral capsid attach to receptors on the host cell; this attachment process is essential to viral infectivity and explains why viruses may only infect the cells of certain species or may only infect certain cells or tissues within a given host species. While the infecting virus triggers an immune response in the host, some are capable of suppressing that response by infecting and killing cells that control immunity (e. g. HIV attacks lymphocytes). In addition, while most infected cells are destroyed by viral replication, some viruses enter a latent phase within cells, reactivating in the future to produce chronic or relapsing infections. Many viruses use specific carriers (known as vectors) such as mosquitoes, ticks, bats and rodents that transmit the virus to a susceptible host while others are spread between individuals via blood contact or through respiratory, intestinal or sexual secretions. Of special concern is the fact that mutations within the viral genome may allow viruses to skip from one host (e. g. birds, swine, monkeys) to another (e. g. humans), unleashing pandemics. Many common human infections are produced by viruses; these include the common cold, influenza, mononucleosis, herpes infections (including shingles), viral hepatitis (A, B, C and others), HIV, viral gastroenteritis, conjunctivitis, viral pneumonia, encephalitis, viral meningitis and viral infections of the heart, including pericarditis and myocarditis. While viruses do not respond to antibiotics, specific antiviral agents may control (though not cure) chronic disease (such as HIV, Hepatitis B and Hepatitis C) or may modify the severity of acute infection (as in influenza and herpes infections). However, in most viral infections, treatment is, for now, purely symptomatic and supportive. On the other hand, vaccines are capable of preventing some viral infections (e. g. erpes simplex, measles, mumps, rubella, varicella, Hepatitis B) or reducing the severity of an acute infection (e. g. influenza). Beyond the acute or chronic illness that they produce, some viral infections (such and Hepatitis C and certain strains of herpes simplex) are known to be precursors of malignancy. Finally, many researchers suspect that viruses play a role in the pathogenesis of chronic illnesses such as multiple sclerosis and autoimmune disorders. development of viruses (images)