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It is important to understand these mechanisms because the clinical presentation and features will depend on their underlying mechanism provera 2.5 mg overnight delivery menopause 34. For reentry to occur buy provera master card menstruation in africa, two distinct conducting pathways must be linked around an area of nonconducting tissue provera 2.5 mg with amex menstruation tent. One limb of the circuit must display slow conduction while the other limb has a long refractory period (Fig. This type of arrhythmia can be terminated if one or both limbs of the tachycardia are disrupted. They usually have a rapid onset and offset (usually in a single beat) and may present with rates above 300 bpm. With abnormal automaticity, there is either abnormally fast activation of cells that exhibit automatic function or the development of spontaneous depolarization in cells that typically do not possess automaticity. Abnormal automaticity often has a metabolic cause (electrolyte disturbances, thyrotoxicosis, hypoxia, ischemia, etc. It can occur in normal children but is frequently seen in acutely ill children and often exacerbated by intravenous sympathomimetics. The arrhythmias caused by abnormal automaticity show behavior similar to sinus rhythm in that they speed up and slow down according to metabolic and sympathetic changes and are generally refractory to direct current cardioversion. The third, and most rare mechanism of tachyarrhythmia is triggered activity, which has features of both automaticity and reentry. This is the result of an after-depolarization, which is an abrupt change in the membrane potential during the action potential (early after-depolarization) or following full repolarization (delayed after- depolarization). This rapid change in the action potential may serve as a stimulus for a subsequent action potential which can ultimately produce or induce a sustained arrhythmia. A: Reentry involves two interconnected limbs of tissue that conduct electrical impulses with an area between the two with no electrical conduction. B: If a premature impulse occurs, it may block in the rapidly conducting limb and conduct down the slow limb only. C: When the impulse reaches the connection between the two limbs, the faster conducting limb is no longer refractory and able to conduct a retrograde impulse. D: This retrograde impulse then activates the slowly conducting tissue setting up the reentrant circuit. One must realize that these are normal resting heart rates and it is frequently challenging in pediatrics to actually obtaining an accurate resting heart rate. Although heart rates above 220 bpm rarely can be sinus in origin, heart rates in this range should warrant evaluation for an abnormal mechanism of tachycardia. Initiation and termination of tachycardia with a single beat also should raise suspicion for an abnormal mechanism of tachycardia. Syncope is a relatively uncommon presentation of tachycardia in the absence of other symptoms suggesting an arrhythmia or underlying channelopathy, although syncope that occurs while actively exercising may be due to an arrhythmic mechanism. Documentation of the electrocardiographic rhythm during times of symptoms or tachycardia is the cornerstone for differentiation between “normal” sinus tachycardia and abnormal mechanisms of tachycardia. In these cases, it may be necessary to use other diagnostic tools to assist with characterization of the tachycardia. Utilizing vagal maneuvers such as the Valsalva or the dive reflex may alter the tachycardia or often times terminate it. Although this is a strong vagal stimulus, it may be alarming to both patient and parent, and care should be taken in small patients to avoid superficial damage to the skin from the ice. Other Vagal maneuvers such as ocular stimulation, carotid massage, gagging, and rectal stimulation are best avoided in the pediatric setting. Other methods can also be used to help determine the etiology of tachycardia in cases where the mechanism is not clear. The two atrial pacing wires are connected to the white (right arm) and black (left arm) leads. Performing a thorough history is also very important in making a diagnosis of a tachyarrhythmia as palpitations are a common complaint in children and teenagers. Differentiation between tachyarrhythmias and sinus tachycardia due to other causes can be challenging. The onset of tachycardia frequently is described as sudden in both sinus tachycardia as well as tachyarrhythmias. However, if palpitations precede the dizziness, this is more consistent with a true tachyarrhythmia. If dizziness is the first symptom, a tachyarrhythmia is unlikely and the cause is usually sinus tachycardia. Quantification of the heart rate also can be challenging to obtain from a history due to the fact P. Asking the child or parent to tap with his or her hand to approximate heart rate is often a beneficial tool to estimate heart rate. In addition, there are computer apps that can be downloaded to help a patient estimate their heart rate at the time of symptoms. Heart rates that are faster than one is able to count should prompt further evaluation for a tachyarrhythmia. In these particular circumstances, performing an exercise treadmill test may be indicated to elicit an abnormal tachycardia. Several different exercise protocols can be used and the appropriate choice depends on the type of exercise that elicits the tachycardia. The typical continuous escalating protocol (Bruce protocol) may be used or modified to replicate the type of activity that triggers the tachyarrhythmia. Some monitors may be worn for 48 hours or even longer, but it is only beneficial if symptoms occur while the monitor is being worn. When a patient feels their particular symptoms, the patient places the device on their chest and activates it, which then creates a recording of the rhythm at that time. A disadvantage to this system is that the patient must have the loop recorder with them and apply it to their chest during an episode of symptoms to record an event. These devices can also be programmed to automatically record the rhythm if the heart rate exceeds or drops below a certain set rate. They can be set up to record events automatically or can be triggered by the patient with an external activation device. The latest generation of loop recorder can then be automatically downloaded with the information sent through the internet without the patient having to actively participate. An implantable loop recorder can be useful in pediatric patients for determining the presence or absence of an arrhythmia during symptoms of syncope, near syncope, and palpitations when conventional diagnostic testing is inconclusive (7). The drawback is the necessity for a minor surgery to implant the device with the need to remove the monitor when it is no longer needed or when the battery life ends (typically around 3 years after implantation). However, newer implantable monitors can be “injected” subcutaneously through an incision around 5 mm wide.

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The ence of a prominent coarctation shelf should stimulate the decision to open the atrial septum should not be based on echocardiographer to return for a repeat study within a day or a Doppler gradient across the atrial septum purchase provera in india pregnancy test eva. In addition buy provera 10mg with mastercard menopause memory loss, careful measure- opening of the septum can result in excessive pulmonary ments must be taken of the proximal aortic arch order provera amex womens health queensland, distal aortic blood fow and metabolic acidosis. When the z It is generally not advisable to consider balloon dilation value is smaller than −2 the arch segment should be consid- of an obstructive pulmonary valve when there is a single ered hypoplastic and particularly careful study of the internal ventricle with obstruction to pulmonary outfow. As result in excessive pulmonary blood fow which can be just discussed in the anatomy section above, obstruction to sys- as problematic as inadequate pulmonary blood fow. Many patients achieved surprisingly good pal- A basic premise of the management of a single ventricle liation with both the classic Glenn shunt as well as the bidi- today is that the natural history of an untreated single ven- rectional Glenn shunt during the 1950s and 1960s. Although a small subset of During the 1960s homografts were introduced by Ross patients with single-ventricle physiology can have a balance and Barratt-Boyes both as valves and as valved conduits (see of systemic and pulmonary blood fow over the long term, Chapter 14, Choosing the Right Biomaterial). He and his cardiologist Choussat enu- needs to be paid very early in infancy or ideally in the neona- merated a list of 10 conditions which were felt to be impor- tal period to preventing excessive volume or pressure loading tant for patients undergoing the Fontan procedure. Following description of the to protect the pulmonary vascular bed as well as to prevent Ross procedure, that is use of the pulmonary valve as an distortion of the central pulmonary arteries. Surgical proce- autograft,28 Kreutzer in Argentina29 applied the concept of dures must also preserve sinus node function. Although it is possible to defer the subsequent Fontan the need for a nongrowing homograft conduit. In addition, procedure for many years this is not always possible (see the posteriorly placed anastomosis was less prone to sternal below). Kreutzer also found that it was not necessary to a fenestrated Fontan procedure within 1–2 years of a bidirec- place a valve at the atriocaval junction. The Fontan Kreutzer tional Glenn shunt so long as the child is making satisfactory procedure was not widely applied during the 1970s. It is critically important that the patient be moni- patients with tricuspid atresia had suffered the consequences tored very closely during this time to ensure that the bidirec- of poor palliation, for example excessive pulmonary blood tional Glenn circulation is functioning adequately and that fow from a Waterston shunt with concomitant distortion of the child is not developing an excessive degree of cyanosis. Patients who had excessive pulmo- nary blood fow were at risk of having developed pulmonary vascular disease. Laboratory studies by William Glenn at Yale led to the was it suffcient to close the atrial septum as had been the development of the classic Glenn shunt in 1958. Patients with hypo- Glenn shunt involves division of the right pulmonary artery plastic left heart syndrome required baffing of the pulmo- with end-to-side anastomosis of the distal divided right pul- nary venous return to the tricuspid valve. The atriocaval junc- to be particularly troublesome and was frequently a site of tion is subsequently ligated and the proximal divided right obstruction. A variation of the classic right atrial pressure compressed the pulmonary venous baffe Glenn shunt was the bidirectional Glenn shunt. This concept appeared to extracardiac conduit and does not involve division of the be supported by the Kawashima procedure33 in which it was crista terminalis with subsequent risk of sinus node dysfunc- found that a virtual Fontan-type procedure could be achieved tion or atrial conduction delay. The lateral tunnel concept was most simply constructed in conjunction The ultimate goal of the sequence of surgical procedures that with a double cavopulmonary anastomosis. Interestingly, de are undertaken for the patient with the single ventricle is to Leval and colleagues34 independently developed the concept achieve optimal systemic oxygen delivery for as low a sys- of a lateral tunnel Fontan by studying the hydrodynamics of temic venous pressure as possible. This goal is thought to be an atriopulmonary connection versus a lateral tunnel-type best achieved by optimizing compliance of the single ven- connection. Thus growth In the mid-1980s, Hopkins35 suggested that the bidirec- of the branch pulmonary arteries must be optimized and tional Glenn was a useful adjunct for palliating the patient they must be kept free of distortion and scarring. Ideally, the procedures should minimize the probability of In 1989, we reported the bidirectional Glenn as an interim late tachyarrhythmias and late bradyarrythmias, should opti- step for patients with hypoplastic left heart syndrome. Staging of the Fontan for patients with hypo- Optimizing Ventricular Compliance plastic left heart syndrome was associated with a remarkable One of the most serious impediments to maintaining opti- reduction in mortality. Therefore, the treatment strategy must not only to the practice of leaving the patent foramen ovale open in carefully exclude the presence of outfow obstruction but also patients following repair of tetralogy of Fallot as empha- anticipate its potential development. The premise that has evolved in cedure it was found that patients had a very much smoother managing patients with a single ventricle is that any volume and more rapid postoperative course. A relatively mild loading of the ventricle should be minimized as early in degree of cyanosis was well tolerated by these patients who life as possible in order to maintain long-term compliance. On the other However, this premise has never been tested by clinical tri- hand, elevated right atrial pressure was poorly tolerated by als. It is interesting to conjecture whether a similar premise young patients and frequently led to a syndrome of worsen- applies for patients with biventricular circulation. Surely ing fuid retention associated with deteriorating myocardial regular exercise and frequent episodes of ventricular volume function. It was load as is the case for the single ventricle, can in a relatively hoped that this would reduce the problem of late arrhythmias short time result in a dilated poorly contractile ventricle that which were being seen with increasing frequency in patients has effectively gone over the top of the Starling curve. Surgical procedures on the pulmonary arteries should Pulmonary Arterial Shunt (Video 25. If the child return with obstruction this must be repaired as early in life is duct dependent, prostaglandin E1 should be continued and as possible. If there is restriction at the level of the atrial sep- the distal anastomosis of the shunt should be placed on the tum in the setting of obligatory left to right fow at the atrial branch pulmonary artery contralateral to the site of ductal septal level then the atrial septum must be surgically excised insertion (Fig. Balloon atrial septostomy is not nosed, for example an arterial oxygen saturation of less than adequate in this setting. It is important that the approach is through a Surgery for Inadequate Pulmonary Blood Flow median sternotomy and not through the more traditional tho- Caused by Pulmonary Outfow Obstruction 48 racotomy approach though there is a greater risk of exces- By far the commonest cause of inadequate pulmonary blood sive pulmonary blood fow when using this approach. The fow in the neonate or young infant with single-ventricle most important advantage of the sternotomy approach for the physiology is obstruction to pulmonary outfow. If the ductus patient with a single ventricle is that dissection of the pul- has closed and if the arterial oxygen saturation is consistently monary arteries occurs very centrally so that distortion of less than 70–75%, then the neonate should undergo place- the lobar branches is highly unlikely to result from the sur- ment of a systemic to pulmonary arterial shunt. The sternotomy approach has the cosmetic advantage of a single incision for all three stages of surgical palliation. Potential Disadvantages of a Systemic There may be a lower risk of thoracotomy-induced scoliosis. Pulmonary Arterial Shunt In our experience, the incidence of Horner’s syndrome is also The most important risk of a systemic to pulmonary arte- decreased with the sternotomy approach. The growth potential, such as the classic Blalock shunt, Waterston mechanism is most likely a positive feedback loop in which shunt, or Potts shunt. All of these shunts can result in a pro- the low diastolic pressure resulting from pulmonary blood gressive increase in pulmonary blood fow over time. They fow throughout the cardiac cycle results in a fall in cardiac also have a higher risk of distortion of the pulmonary arteries output which further reduces diastolic pressure and coronary relative to the modifed Blalock shunt which uses a Gore-Tex perfusion. Typically, The shunt should be anastomosed to a central pulmonary artery where it is anticipated that the subsequent Fontan the child will have an oxygen saturation of greater than 83 anastomosis will take place. It can be very diffcult to resuscitate a neonate in this pulmonary artery which results from the shunt can be incor- setting with cardiopulmonary resuscitation alone. Excessive shunt size can also result over time in an the site selected for the proximal anastomosis are critically increase in pulmonary vascular resistance.

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Furthermore cheap 10 mg provera visa women's health clinic london ontario king street, if an administrator assumes additional roles and responsibilities buy generic provera 10 mg on-line breast cancer 00 blogspot, he or she will be in danger of being assigned those roles and responsibilities permanently without the beneft of more resources provera 2.5mg mastercard women's health clinic jeddah. Public administrators should be generally aware of the capabilities of their organization’s personnel and the resources avail- able to them. Political Disposition Public agencies have to contend with political pressures, both internal and external, particularly from other public organizations, the public, and elected ofcials. Tese entities hold public administrators accountable for their actions and decision- making processes. When decisions are being formulated, public administrators should always keep in mind that there can potentially be negative consequences to risky or incomplete decision-making processes that can signifcantly impact Guidelines and General Information ◾ 17 their organization. At times a public administrator may make a decision based on the political boundaries from elected ofcials or the public. While the decision may not be the most efective or the preferred action by the administrator, it may be the best decision that can be made under the political realities faced by his or her organization. Administrators at the local, state, or federal level should be careful to avoid entanglement with other levels of administrators, which can potentially lead to disaster. The roles of federal, state, and local administrators should be clearly defned by an emergency plan of action, which should allow for cooperation and resources to be utilized efectively. Time During a disaster or emergency, a public administrator should keep the variable of time in mind when considering a plan of action or response. Does the response or plan that the administrator has formulated have time to work within a given set of parameters? If a terrorist destroys a public building and produces a great deal of rubble, does the public administrator have enough time to mobilize digging equipment or heavy lifting equipment to assist frst responders? If time is a signif- cant factor (as it almost always is in any emergency situation), how does the public administrator get resources to the frst responders more quickly to save survivors? In some situations, however, it may be more prudent to allow for more time than usual. An example of this would be a hostage situation in which the situation is contained but law enforcement needs as much time as possible to apprehend the aggressors peacefully and free the hostages safely. Threat Level/Threat Assessment A public organization should take an inventory of what threats could be posed to its community to prepare efective emergency response plans. Tese threats may include such situations as a nearby nuclear plant accidentally releasing radioactive material, like with Tree Mile Island, or a chemical plant nearby that releases toxic chemicals into the environment, which happened in Bhopal, India (Perrow, 1999). Other organizations will have to plan for recurring natural disasters, such as win- ter storms, earthquakes, foods, hurricanes, tornadoes, fres, and tsunamis. Some public organizations will have to assess threats diferently since their mission is to respond to disasters across a wide geographical area, such as the U. On December 20 you learn that a beneft performance is to be held on December 26 at the old theater hall (Richmond Ten and Now, 2007). The hall is very rickety and you believe that only small audiences, if any, should be allowed inside the building to watch a perfor- mance (Watson, 1812). As the city fre marshal it would be important to frst determine if the theater should even be allowed to operate for public events due to the condition of the structure. If the structure is safe for public events to be held in the auditorium, then a strict room capacity limit should be posted for the auditorium and an evacuation plan should be formulated for fre and medical services should an incident occur. The city fre marshal should communicate these concerns to all of the department heads in the municipality. Should an emergency occur, it will be necessary to utilize an array of city services to ensure the well-being of the patrons and citizens that are attending the performance. How will you enforce the rules and regulations your department has formulated for the theater to operate? If the theater owners do not comply with the regula- tions that have been set forth, it is the responsibility of the city fre marshal to shut down the performance hall for noncompliance of municipal guidelines. Stage 2 of the Disaster On December 23, you received word that a very well-known actor will be per- forming at the beneft performance. The theater has already sold 300 tickets and the building will need to be heated adequately since the weather is extremely cold outside (Watson, 1812). At this point the city fre marshal should remind the theater operators of the maximum occupancy level for the performance hall. If there is additional demand beyond the safe capacity, the theater could then consider running multiple performances. Since heating will be used in a wooden structure, suitable frefghting apparatus should be on hand to con- tend with a potential fre. Additionally, escape routes should be well marked and free of clutter in the aisles and hallways. The city manager should be made aware of any concerns as well as the police chief and the director of planning and zoning. In addition, it would probably be a good idea to discuss the issue with the local medical community in case an incident did occur. How will you enforce the rules and regulations your department has formulated for the theater to operate? At any point, city ofcials have the authority and responsibility to close the theater for noncompliance of the rules. Failure to close the theater without the proper safety guidelines will cause the munici- pality and its administration to be liable for any incident that occurs. Tis can result in criminal prosecution or civil lawsuits, to not only the theater operators but also the municipality’s administrators. Stage 3 of the Disaster On the day of the scheduled performance, December 26, you learn that 600 people have bought tickets to the beneft performance and will be attending (Richmond Ten and Now, 2007). The city fre marshal should at this point coor- dinate with other city ofcials and ensure that no more than 300 people are allowed to enter the performance hall. If the theater owners are so inclined, they can have a second showing the next evening. You need to calmly communicate your concerns to the patrons that are attempting to gain entrance to the theater as the surplus attendees are prevented from entering the performance hall when the safe occupancy level has been reached. You should tell the patrons who were not allowed entrance that they can contact the theater owners in regard to either gaining entrance to a second showing or receiving refunds for their tickets. Additionally, you should provide written notice to the the- ater owners that they are in violation of safety codes and that fnes could be levied against them if they do not comply with safety guidelines that were previously set forth. If, despite your concerns, other city ofcials allow 600 people into the performance hall (which is actually what happened in this case study), then you will need to have sufcient frefghting equipment on hand, medical and frefghting personnel to attend to any emergency, and a contingent of police ofcers for crowd control. In addition, there should be cooperative agreements in place with other municipalities for medical assistance and frefghting resources if needed. Stage 4 of the Disaster Two ceiling lamps ficker and then sparks fall onto the wooden stage area (Richmond Ten and Now, 2007). Considering the age of the performance hall and the condi- tion of the overall building, this should be a major cause for concern. You should evacuate the theater immediately and try to get as many people out of the building as safely as possible. The sec- ond action item that should be undertaken is to get frefghters into position quickly to extinguish the fre as soon as possible.

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When expressed in cells on their own proven 2.5mg provera women's health clinic jber, neither is able to activate gene expression purchase provera american express womens health vidalia georgia. That is buy cheap provera 10 mg online women's health clinic tampa fl, only if the two hybrid proteins are able to interact with each other will gene expression occur. One of the advantages of performing interaction screening in yeast is that a large number of reporters are available for use in yeast – these include those shown in Table 6. As originally described, the two-hybrid system was used to detect specific interactions between two known proteins, sometimes called the bait and prey, in yeast (Fields and Song, 1989). Interacting partners can be isolated from the library as those that activate the expression of the reporter gene (Figure 6. This gives an unacceptably high background level of false positives in the screen – that is, many yeast colonies will be able to activate the reporter gene even though they do not contain proteins that interact with each other. If the prey fusion is able to bind fortuitously to the promoter of the reporter gene, then it will promote transcription of the reporter even though it does not interact with the bait. This problem can be overcome by screening for the expression of two, or more, different reporter genes. This approach is essential if screening libraries for interacting partners, and two ways in which this can be achieved are shown in Figure 6. Yeast strains harbouring multiple reporter genes, which are different except for the Gal4p binding sites, have been constructed (James, Halladay and Craig, 1996). Colonies are only analysed further if all, and not just a sub-set, of the reporters are activated. An alternative approach is to perform the screen in a yeast strain expressing two different baits and a single prey (Xu, Mendelsohn and Brent, 1997). In this case, activation of only one reporter should occur, and a false positive would be assigned if both reporters become activated (Serebriiskii, Khazak and Golemis, 1999). Some protein–protein interactions, although physio- logically relevant, are very weak. Weak protein–protein interactions may not be sufficiently strong to recruit the transcriptional machinery to the promoter, and consequently the reporter gene will not be activated. It has been estimated that if the binding affinity between the bait and the prey is weaker than about 10–50 µM, then a transcriptional response will not be elicited (Brent and Finley, 1997). Using multiple reporters in the same cell to reduce the number of false positives in a two-hybrid screen. Interactions between the bait and prey should activate all of the reporters and not a sub-set of them. A specific interaction between one of the bait proteins and the prey will result in the activation of only one of the reporter genes. This type of screening is particularly useful if the two bait proteins are closely related to each other to identify a prey that interacts specifically with only one bait (Serebriiskii, Khazak and Golemis, 1999) • Bait protein cannot itself be a transcriptional activator. If the bait is itself an activator then it cannot be used to find interacting partners using the screens described above. The traditional two-hybrid system relies on both the bait and prey proteins entering the eukaryotic nucleus and being able to interact there. For example, a membrane associated protein will be tethered to the membrane and con- sequently unable to enter the nucleus. Some proteins are able to interact within a two- hybrid system even though the interaction is not physiologically relevant. For example, proteins that are normally located in different cellular com- partments or at different developmental stages may be capable of interaction with each other when expressed in the same cell, but they would never nor- mally be expressed together in their natural state. It is also possible that the bait and prey do not directly interact with each other, but that their apparent association is mediated by another cellular protein. Interaction mating is now widely used to screen large numbers of bait proteins (Finley and Brent, 1994). A panel of different baits are constructed and transformed into haploid yeast of one of the two mating types (a or α). A prey library is transformed into a yeast strain of the opposite mating type and the different strains are mated. This method allows for rapid screening of multiple baits in a single experiment (Colas and Brent, 1998). The two-hybrid system offers excellent opportunities to identify proteins that interact with each other. The caveats described above mean that the technique will not work for every protein but, as we will see in Chapter 10, genome-wide protein interaction maps have been constructed using data collected from two- hybrid screens (Uetz et al. The principles described above for the Gal4p based systems hold true for each of these modified versions. This approach is useful in the identification of proteins that regulate the promoters of known genes (Wang and Reed, 1993). In a similar vein, Licitra and Liu developed a system to detect small-molecule–protein interactions (Licitra and Liu, 1996). This is useful to screen for drugs that disrupt the interaction between the proteins and thereby allow the cells to survive through the non-expression of the reporter (Huang and Schreiber, 1997). The analysis of mutations is especially useful in the elucidation of protein function. Mutations that either reduce the activity of the protein, or allow the protein to behave in an abnormal way, can be used to ascribe particular functions to individual portions of proteins. Naturally occurring mutations have, however, been used to isolate genes and describe specific functions for their encoded proteins. Prior to the explosion in molecular biology techniques in the 1970s and 1980s, increased mutation rates were usually obtained by treating whole cells with either a physical or a chemical mutagen. For example, the treatment of micro-organisms or Analysis of Genes and Genomes Richard J. Once produced, these changes will be passed from generation to generation as the cells divide. For example, the mutations produced are random – they can occur anywhere within a genome and are not restricted to individual genes or parts of genes. Additionally, highly developed and specialized screening procedures are required to identify mutations that have occurred within individual genes. This is relatively straightforward for mutations occurring in genes that encode, for example, one of the enzymes of a metabolic pathway. Mutations that destroy the activity of one member of the pathway are likely to lead to the formation of an organism that is unable to metabolize a particular nutrient. Traditional forms of mutagenesis also suffer, since the observed phenotypic change in a screen may not be a result of a mutation within a single gene. Additionally, multiple mutations may be required (perhaps when multiple redundant genes occur within the same cell) before a phenotypic change can be observed. Single base changes may result in various alterations to the amino acid sequence of the protein encoded by the gene at the regions of the changed bases.