Feather color in parakeets is produced by the blending of pigments produced from
ID: 24769 • Letter: F
Question
Feather color in parakeets is produced by the blending of pigments produced from two biosynthetic pathways shown below. Four independently assorting genes (A, B, C, and D) produce enzymes that catalyze separate steps of the pathways. For the questions below, use an uppercase letter to indicate a dominant allele producing full enzymatic activity and a lowercase letter to indicate a recessive allele producing no functional enzyme. Feather colors produced by mixing pigments are green (yellow +blue) and purple (red +blue). Red, yellow, and blue feathers result from production of one colored pigment, and white results from absence of pigment production.Use an underscore _ for alleles that can be either dominant or recessive in the format A_B_C_D_. If the genotype does not matter at a locus use two underscores __.
A: What is the genotype of a pure-breeding purple parakeet strain?
B: What is the genotype of a pure-breeding yellow strain of parakeet?
Explanation / Answer
In both animals and humans brucellosis may occur in an acute, subacute or chronic forms. In both cases once acquired chronic brucellosis can continue for a lifetime. B melitensis, B abortus, and B suis become chronic in humans but current opinion suggests that B canis seldom does. Scientific evidence indicates that Brucella is an intracellular parisite. In the course of infection Brucella can enter and overcome the defenses of phagocytes and replicates within them. There is also evidence that Brucella can impair the release of cytokines such as INF-?, Rodriguez-Zapata in 1996 [10] and [11] and TNF-a, Dormand (2002) [12] preventing the action of CD8+. Also it has been shown that Brucella can inpair the function of Natural Killer Cells, Billard (2007) [13] and prevent apoptosis of infected maccrophages, Tolomeo (2003) [14]. These effects favour chronic illness. The infected phagocytes are a recevoir of infection which are protected from the general immune system response and probably inhibit antibiotic effectiveness. Such infected phagocytes can carry the disease to every organ in the body. Once settled within organs Brucella can cause locallised leisons and cysts which may be very small. It is probable that such leisoms can act as a recevoir of infection over long periods abstracted from the influence of the immune system and resistant to antibiotics. In humans B melitensis has the highest prevalence, is the most virulant and is also the most likely to become chronic [15] but milder in B abortus. The onset of brucellosis may be a sudden acute attack or may be slow and insiduous. Acute attacks are usually not difficult to diagnose if the right serology tests are used. At least 2 antibody serology tests are needed measuring both immunoglobulin M (IgM) and immunoglobulins G (IgG). Seroconversion for Ig) usually occurs at about seven days and that for IgG and immunoglobulin A (IgA) slightly later. The antibody response of individual patients may vary considerable with some false negative results. Also the tests can be subject to technical problems giving both false positive and false negative results. The culture test on blood provides a virtulally certain diagnosis but can take up to 6 weeks to complete when a rapid diagnosis is often required. The culture test does not work well for B abortus posibly because with this milder form of the illness patients do not become bacteremic. It can also be used to differentiate between B melitensis, B abortus, and B suis. The culture test can also be used to measure tissue and aspirate samples from infected organs. Acute attacks of brucellosis usually starts with an influenza like illness with fever, sweating, myalgis, headaches and possibly a high temerature. Brucellosis was once called "undulant fever" because of a perceived fluctuating temperature profile but this does not occur in all cases. Without treatment brucellosis can become established amd become chronic in at least 30% to 50% of cases, Hughs (1897) [16] and Spink [17]. Before antibiotics were introduced the only treatment that worked was repeated injections of vaccine although the usefulness of this treatment has been disputed. Antiboitics were gradually introduced from about 1950 onwards. A range of antibodies that work against gram positive bacteria can be used but doxycyclin, streptomicin, rifampicin, ciprofloxicin and TMP-SMZ have proved the most useful. Combinations of 2 or 3 antibiotics work better than single antibiotics. The most widely used treatments are combinations of doxycyclin plus riframpicin or doxycline plus streptomicin with a duration of at least 8 weeks. For best results treatment should be started as soon as possible after the initial infection. If treatment is delayed and Brucella becomes established with locallised leisons and complications treatment becomes less succesful. At least 10% of patients who are treated with antibiotics relapse within 2 years from the start of the infection. Complications can be severe and affect any organ of the body. The most problematical complications relate to the skeleton, liver, spleen, urinogenital tract, panceas, heart, lungs, and nervous system including the brain. Death can occur in up to 2% of cases and this is usually related to complications affecting the heart and the nervous system. Symptoms of illness vary widely depending on the mode of infection. Chronic brucellosis is usually defined as illness which continues beyond 12 months. The most likely caused of illness becoming chronic are: severe illness with complications, lack of treatment, delayed treatment, and inadequate treatment, Landau (1999) [18]. Patients are ofter described as cured after antbiotic treatment but the extent to which patients make a completely recover is unknown particularlt considering the problems of diagnosing chronic brucellosis as discussed below). Recent research indicates that 70% of patients retain Brucella DNA in their sytems for more than 2 years after treatment despite apparent cure, Pappas (2008) [19]. In up to 50% of cases the onset of brucellosis can be insiduous [20]. This makes diagnosis very difficult and may increase the likelihood of chronic illness. Chronic brucellosis can be very difficult to diagnose. Problems relate to vague generalised symptoms with nothing specific to brucellosis and false negative serology test results. The symptoms are similar to acute brucellosis but less severe. The main ones are weakness, fatigue, headaches, backache, fever usually without obvious temperature rise and general aches and pains, dispepsia, and depression. Patients often appear to be superficially well with no unusual blood test results. The culture test hardly ever works in chronic brucellosis. Antibody serology tests for IgG and IgA work better than tests for IgM. All tests fail in a significant proportion of cases including imdirect enzyme linked immunosorbent assay (iELISA). There is a widespread opinion that iELISA can diagnose chronic brucellosis better than other tests. This is incorrect. In practice in most cases the results of antibody serology tests in chronic brucellosis are arbitory. The currently established taxonomy of the Brucella genera based on both biotyping and genotyping is: Phylum - Proteobacteria. Class - Alphaproteobacteria. Order- Rhizobiales. Family - Brucellaceae. In North American, European countries and other developed countries B abortus infection in cattle had been eliminated or reduced to very low level. This has taken about 70 years and in most countries and became effective in about the 1980s. Some countries still have sporadic outbreaks and there are localised risk in the USA and Canada due to contact between cattle and infected wild bison or elk. Cattle can also become infected with B melitensis and B suis by contact with wild animals. Efforts to eradicate ‘’B abortus’’ from cattle has been a slow, difficult and tortuous task. Four methods of eradication have been used: Testing animals and removing reactors. Testing and completely culling infected herds. Vaccination. A combination of both vaccination and test/slaughter or culling. An effective control of B abortus infection in cattle requires the following elements: Surveillance to identify infected cattle herds. Prevention of the transmission to non-infected cattle herds. Eradication of infected reservoirs to eliminate the sources of infection and protect clean herds being re-contaminated by the reintroduction of the disease. In the early part of the twentieth century the main problem was considered to be the economic losses caused to farmers by B abortus infection in cattle and not human health. Attempts were made by individual farmers to eradicate it from their herds by eliminating infected animals. In practice this was very difficult and most attempts failed because the disease was insufficiently understood. A major problem was the necessity of introducing new and potentially infected animals into a cleaned closed herd since the disease could spread rapidly back through the whole herd. In these early days there was also a lack of local and central government support which was later found to be essential. Slowly government measures were introduced to help farmers. The aim of such measures was to find all infected herds, to restrict existing infection to known reservoirs and to eradicate brucellosis from such reservoirs. In the USA laws were gradually introduced to ban the sale of infected cattle except for slaughter and by 1934 a number of US States had set up voluntary control and certification programmes to test blood from cattle using government laboratories. It is important to note that measures to eradicate ‘’B abortus’’ in wealthy countries may not work in poorer ones. Problems in general relate to cost. These include lack of finance for veterinarian services, the financial losses to farmers related to the slaughtering of cattle and problems in segregating infected animals. The procedures which have been found necessary to effect eradication are as follows: Segregation. An important part of the control of brucellosis depends on segregation and slaughter of infected animals. In order for this to work it was essential to provide adequate compensation for slaughtered cattle to farmers. The greatest risk of spreading the disease is at parturition because the aborted calves, placenta and vaginal secretions can be very heavily infected. Therefore all pregnant cattle should be separated at this time because even apparently healthy cows can be a high risk. *Tagging. Infected cattle going through markets can be a serious problem in causing the spread of brucellosis. There was a need to test and identify such animals. There was also a need to trace infected cattle found at slaughter or in markets back to the infected herds from which they came. A comprehensive system of tagging of cattle has been found to be essential. Serology Test. Serology and milk tests have played a vital role in eradication of brucellosis but it should be said that no test has been developed which works in all cases. In the early days the Wright's agglutination test (SAT) was the only test available
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.