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If the differences are significant and migration and non-random mating can be discounted anxiety night sweats discount serpina 60 caps on-line, then there is evidence that directional selection is occurring in the population anxiety chest pain order serpina 60caps with visa. Selective breeding over many centuries has produced many different breeds anxiety symptoms vs heart attack buy serpina 60 caps otc, such as b, the Guernsey. Desired features include docility (making the animal easier to control), fast growth rates and high milk yields. Individuals showing one or more of these desired features to a larger degree than other individuals are chosen for breeding. Over many generations, alleles conferring the desired characteristics increase in frequency, while those conferring characteristics not desired by the breeder decrease in frequency. A bull cannot be assessed for milk production since this a sex-limited trait (note that this is not the same as sex-linked). It is important to realise that selective breeders have to consider the whole genotype of an organism, not just the genes affecting the desired trait, such as increased milk yield. Suppose that the chosen parents come from the same environment and are from varieties that have already undergone some artificial selection. It is likely that such parents share a large number of alleles of background genes, so the offspring will be adapted for the same environment. But suppose instead that one of the chosen parents comes from a different part of the world. It may show the trait being selected for, but it may not be welladapted to its environment. Black Sea Caspian Sea Assyria Mediterranean Sea Mesopotamia Phoenicia Euphrates Tigris Lower Egypt Persian Gulf Red Sea Upper Egypt Nile Figure 17. Crop improvement the same problem is seen when a cross is made between a cultivated plant and a related wild species. Although most species will not breed with a different species, some can be interbred to give fertile offspring. Such species are often those that do not normally come into contact with one another, because they live in different habitats or areas. The wild parent will have alleles that are not wanted and which have probably been selected out of the cultivated parent. It was not until the 20th century that we really understood how we can affect the characteristics of crop plants by artificial selection and selective breeding. But, although these early farmers knew nothing of genes and inheritance, they did realise that characteristics were passed on from parents to offspring. The farmers picked out the best plants that grew in one year, allowing them to breed and produce the grain for the next year. Over thousands of years, this has brought about great changes in the cultivated varieties of crop plants, compared with their wild ancestors. Today, selective breeding continues to be the main method by which new varieties of crop plants are produced. In some cases, however, gene technology is being used to alter or add genes into a species in order to change its characteristics. Much of it is grown to produce grains rich in gluten, which makes them good for making bread flour. For making other food products such as pastry, varieties that contain less gluten are best. Chapter 17: Selection and evolution Breeding for resistance to various fungal diseases, such as head blight, caused by Fusarium, is important, because of the loss of yield resulting from such infections. Successful introduction of an allele giving resistance takes many generations, especially when it comes from a wheat grown in a different part of the world. Its aim is to support the development of new varieties by screening seed collections for plants with traits such as disease resistance, or climate resilience (Figure 17. Any plant with a suitable trait is grown in large numbers and passed to the commercial breeders. This makes them easier to harvest and means they have higher yields (because they put more energy into making seeds rather than growing tall) (Figure 17.
Ron and colleagues (1998a) reported on mortality to anxietyzone symptoms poll discount 60 caps serpina with visa the end of 1990 in the Cooperative Thyrotoxicosis Therapy Follow-up Study venom separation anxiety serpina 60caps with mastercard. The mean length of follow-up was 21 years anxiety yahoo purchase serpina 60 caps without a prescription, and 51% of the subjects had died during the study period. A nonsignificant increase in mortality from thyroid cancer was seen with increasing 131I administered activity-when deaths occurring in the first 5 years after treatment were excluded, there was no evidence of a relationship with total activity; it is therefore likely that the underlying thyroid disease played a role in the observed cancer increase. Cancer incidence was also studied in 4557 patients who received 131I therapy for hyperthyroidism in Sweden between 1950 and 1975 at Radiumhemmet, Sweden (Holm 1984). The risk of leukemia mortality in this cohort was studied further by Weiss and colleagues (1995), using a casesubcohort approach. A Swedish cohort of 20,024 patients who received X-ray therapy between 1950 and 1964 for painful benign conditions of the locomotor system (including arthrosis and spondylosis) was followed for cancer incidence and mortality until the end of 1988 (Damber and others 1995). Average conversion factors between surface dose and mean absorbed dose in the red bone marrow were estimated by treatment site (for six sites), based on the treatment records of random samples of 30 subjects drawn from the cohort (Damber and others 1995). The conversion factors were applied to the entire cohort and used for stratification of subjects in different levels of exposure. Thyroid Diseases Iodine-131 is currently the treatment of choice for hyperthyroidism, largely because no serious side effects are known. Several studies of patients treated with 131I for hyperthyroidism have been carried out in the United States, Sweden, and the United Kingdom. The occurrence of leukemia and of thyroid neoplasms (both benign and malignant) was studied among 36,050 patients treated for hyperthyroidism between 1946 and 1968 and included in the Cooperative Thyrotoxicosis Therapy Follow-up Study (Saenger and others 1968; Dobyns and others 1974). Approximately 20,000 subjects had been treated Copyright National Academy of Sciences. Cancer diagnoses in these patients were identified from the Swedish Cancer Registry for 1958 to 1976. There was no increased risk of cancer as a whole or of leukemia in this population. The risk of cancer was studied in 10,552 patients (including the 4557 in the previous study) treated for hyperthyroidism with 131I in seven hospitals in Sweden between 1950 and 1975 (Holm and others 1991). The mean follow-up time of subjects who survived more than a year after treatment was 15 years, with a maximum of 28 years. Significant increases were seen for cancers of the lung and kidney and, among 10-year survivors, for cancers of the stomach, kidney, and brain. A population-based study of cancer incidence in a cohort of 7417 patients treated with 131I in the West Midlands region of the United Kingdom between 1950 and 1991 was carried out (Franklyn and others 1999). The subjects were followed up for cancer incidence and mortality from 1971 to 1991. Studies of patients treated for ankylosing spondylitis, benign breast disease, benign gynecological disease, and peptic ulcer have provided valuable information for the quantification of radiation risk estimates for cancers of the lung, breast, and stomach and for leukemia. These estimates are reviewed in detail, and compared with risk estimates derived from other medical exposure studies, in section "Evaluation of Risk for Specific Cancer Sites. Radiotherapy for Benign Disease Among Children Tinea Capitis Between 1948 and 1960 nearly 20,000 children, primarily immigrants to Israel or children of immigrants from North Africa and the Middle East, were treated with radiation for tinea capitis (ringworm of the scalp) in Israel (Ron and others 1988b). This treatment modality was used in other countries as well, and a study also was carried out in New York (Shore and others 1984). In Israel, mortality in a cohort of 10,834 irradiated children, 10,834 matched comparison subjects, and 5392 sibling controls was studied by Ron and colleagues (1989). Crude dose estimates were derived from treatment information (dosage, area), age of the child, and the use of filtration. Radiotherapy in childhood was associated with an increased risk of mortality from tumors of the head and neck (particularly brain and thyroid tumors) and leukemia. The dose reconstruction method used was improved compared to the above paper, relying heavily on dosimetric studies and measurements in a simulated phantom model of a 6-year-old child. Doses used in the treatment of benign conditions were generally not as high as those used to treat malignant disease, so that cell-killing effects do not predominate, survival after treat- Copyright National Academy of Sciences. Delivered doses ranged from 3 to 6 Gy depending on the portion of the scalp, with lower doses to the skin of the face and neck (0. In the irradiated group, 41 subjects had a diagnosis of basal carcinoma of the scalp or face, compared to 3 in the control group. The minimum latent period was long (about 20 years); skin cancers were more pronounced on the face, where the potential for exposure to ultraviolet is higher, and were restricted to Caucasians although one-quarter of the study population was African American.
Homeostasis in plants It is as important for plants to anxiety symptoms 6 year old cheapest generic serpina uk maintain a constant internal environment as it is for animals anxiety 9 to 5 best buy for serpina. For example anxiety buy 60caps serpina, mesophyll cells in leaves require a constant supply of carbon dioxide if they are to make best use of light energy for photosynthesis. We have seen how low concentrations of carbon dioxide limit the rate of photosynthesis (page 292). Strictly speaking, a stoma is the hole between the guard cells, but the term is usually used to refer to the two guard cells and the hole between them. Stomata may look very simple, but guard cells are highly specialised cells that respond to a wide range of environmental stimuli and thus control the internal atmosphere of the leaf. This glucose biosensor is used to check the glucose concentration in a sample of blood. Even when kept in constant light or constant dark, these rhythms persist (Figure 14. Opening during the day maintains the inward diff usion of carbon dioxide and the outward diff usion of oxygen. The closure of stomata at night when photosynthesis cannot occur reduces rates of transpiration and conserves water. They open in response to: increasing light intensity low carbon dioxide concentrations in the air spaces within the leaf. When stomata are open, leaves gain carbon dioxide for photosynthesis, but tend to lose much water in transpiration. This rhythm persisted even when the plants were kept in constant light b; and in long periods of constant dark c. Cambridge International A Level Biology Stomata close in response to: darkness high carbon dioxide concentrations in the air spaces in the leaf low humidity high temperature water stress, when the supply of water from the roots is limited and/or there are high rates of transpiration. The disadvantage of closing is that during daylight, the supply of carbon dioxide decreases so the rate of photosynthesis decreases. The advantage is that water is retained inside the leaf which is important in times of water stress. Guard cells open when they gain water to become turgid and close when they lose water and become flaccid. A decrease in water potential is needed before water can enter the cells by osmosis. This is brought about by the activities of transporter proteins in their cell surface membranes. The decrease in the hydrogen ion concentration inside the cells causes channel proteins in the cell surface membrane to open so that potassium ions, K+, move into the cell. They do this because the removal of hydrogen ions has left the inside of the cell negatively charged compared with the outside, and as potassium ions have a positive charge, they are drawn down an electrical gradient towards the negatively charged region. The extra potassium ions inside the guard cells lower the solute potential, and therefore the water potential. Now there is a water potential gradient between the outside and the inside of the cell, so water moves in by osmosis through aquaporins in the membrane. The wall adjacent to the pore is very thick, whereas the wall furthest from the pore is thin. Bundles of cellulose microfibrils are arranged as hoops around the cells so that, as the cell becomes turgid, these hoops ensure that the cell mostly increases in length and not diameter. Since the ends of the two guard cells are joined and the thin outer walls bend more readily than the thick inner walls, the guard cells become curved. Guard cells do not have plasmodesmata, so all exchanges of water and ions must occur across the cell surface membranes through the pump and channel proteins. Chapter 14: Homeostasis Stomata close when the hydrogen ion pump proteins stop and potassium ions leave the guard cells and enter neighbouring cells.
Risk assessment An extremely important part of planning any experiment is to anxiety low blood pressure generic serpina 60caps with visa think about the potential hazards involved anxiety symptoms in adults buy cheap serpina 60caps. In biology experiments anxiety symptoms full list generic serpina 60 caps on-line, there often are not any significant risks, and if that is the case then you should say so. Do, though, always mention risk, even if it is just to say that you do not think there is any. If you do identify any significant risks, then you should explain how you would minimise them. This is hot enough to burn the skin, so you would need to take precautions when handling the apparatus in a water bath at that temperature. You should lift the apparatus in and out using tongs, or use heatproof and waterproof gloves. These are the results, recorded to the nearest gram and arranged in order of increasing mass. You may also want to describe how you would use the data to plot a graph, explaining what you would put on each axis and the type of graph you would draw. Using the data to reach a conclusion You may be asked how you would use your collected results to reach a conclusion. Usually, the conclusion will be whether or not the results support your hypothesis. Here, the masses of the lemons were recorded to the nearest whole number, so we can record the mean either to the nearest whole number, which is 96, or to one more decimal place, which is 95. To find the median and mode, you need to plot your results as a frequency histogram (Figure P2. Cambridge International A Level Biology 5 modal class median class Normal distribution 4 Number of lemons 3 Many sets of data produce a symmetrical pattern when they are plotted as a frequency diagram. The interquartile range is therefore the range of mass shown by the remaining 20 fruits, which is 84 g to 105 g. Imagine that you have collected another set of fruits from a different tree, and want to compare the two sets. By concentrating on the middle 50% of the range, you eliminate the fruits with extreme masses at either end of the range. Comparing the interquartile ranges of both sets rather than comparing the complete ranges may give you a better idea of how similar or different the sets are. Chapter P2: Planning, analysis and evaluation Standard deviation A useful statistic to know about data that have an approximately normal distribution is how far they spread out on either side of the mean value. The larger the standard deviation, the wider the variation from the mean (Figure P2. The best way is to set your data out in a table, and work through it step by step. A student measured the length of 21 petals from flowers of a population of a species of plant growing in woodland. Chapter P2: Planning, analysis and evaluation Length of petal / mm the 21 petals measured were just a sample of all the thousands of petals on the plants in the wood and in the garden. We cannot be certain without actually doing this, but there is a calculation that we can do to give us a good idea of how close our mean value is to the true mean value for all of the petals in the wood. Once you have worked out the standard deviation, s, then the standard error is very easy to calculate. The standard error tells us how certain we can be that our mean value is the true mean for the population that we have sampled.