4.3 Golden Rice in the public domain In January 2000, the successful experiments were announced in a paper published in the American journal Science. This, in itself, is significant. Generally, work on genetic manipulation would be published in one of a number of more specialist journals. Publication in a journal like Science indicates that this was important work, likely to be of interest to a wider audience. In its ‘Notes for Authors’, the journal states that ‘Priority is given to papers that reveal novel c
A strategy for ridding the world of VAD? In July 2000, Time magazine announced that a potential solution to VAD had been found – ‘Golden Rice’ (Figure 8). This was a variety of rice that had been genetically modified to introduce β-carotene into the endosperm (part of the grain of the rice). The name arises from the fact that the otherwise white grains of rice are given a golden colour by the presence of carotenoid compounds. The announcement came at the height of the global controversy over genetically modified
2.2 Using A. tumefaciens to genetically modify plant cells Genetic engineers have capitalised on the fact that part of the DNA from the Ti plasmid of A. tumefaciens is integrated into the plant genome during the infection process. Ti plasmids can be isolated and a foreign gene spliced in at an appropriate point, making it possible to transfer the novel gene into the plant. Preamble Your answers to Activity 1 will have revealed that the initial development of commercial GM crops has focused on the introduction of two traits: herbicide tolerance and insect resistance. However, many other traits have been introduced into crops that have yet to be grown commercially on any scale. These traits include characteristics such as resistance to viral, bacterial and fungal infections, stress tolerance (for example to high levels of salt in the soil), changes to flower pigmentation, 1 Genetic manipulation of plants and GM crops: an introduction In this unit we will consider the genetic manipulation of plants, and the production of GM crops. A great deal has been written about the science of GM crops and the controversial issues surrounding their introduction around the world. In the study time available, we will focus on a small number of selected issues. In this unit you'll have the opportunity to learn more about the science that has been used to engineer a range of GM crops, and examine both the science and social concerns Learning outcomes By the end of this unit you should be able to: understand more about the science that underlies the development of genetically modified organisms and in particular how gene transfer is brought about; know something of the potential benefits and uncertainties associated with gene transfer and the high levels of technical ingenuity involved; be better able to understand the science that underpins the development of Golden Rice and understand why the u 3 Summary Hydropower was the earliest means of commercial electricity generation, and currently dominates alternative electricity supply. However, its global capacity for large-scale exploitation is less than six times that currently installed. Growth of hydropower is slow and its contribution to global electricity supply is falling. Both are due to economic factors, the slow pace of large-scale project construction, the remoteness of high-potential sites, and increasing resistance to the social 1 Hydropower Hydroelectric energy is ultimately solar energy converted through evaporation of water, movement of air masses and precipitation to gravitational potential energy and then to the kinetic energy of water flowing down a slope. That energy was harnessed for centuries through the use of water wheels to drive mills, forges and textile works, before being supplanted by coal-fired steam energy. Electricity generation using water turbines, although first centred on constricted streams, has increasing Learning outcomes By the end of this unit you should be able to: explain the principles that underlie the ability of hydropower to deliver useable energy; outline the technologies that are used to harness hydropower; discuss the positive and negative aspects of hydropower in relation to natural and human aspects of the environment. Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: Figure 3 Courtesy of Biophoto Associates; Figu 5 Summary of unit We have seen in this unit that, despite having a high natural abundance, iron is in very short supply because of the insolubility of its oxides and hydroxides. A result of this is that organisms have developed methods for the uptake, transport and storage of iron. Bacteria, in particular, secrete very powerful iron chelators known as siderophores. Of all the iron–siderophore complexes, the iron(III)–enterobactin complex has the exceptionally high stability constant of 1049 mol< 3.1 How do organisms take up iron? Nearly all organisms are able to take up iron. However, only a handful of organisms have had their iron-uptake chemistry studied. The organism that has received most attention (other than human) is a single-cell, prokaryotic bacterium (found in the human large intestine and elsewhere), called Escherichia coli (abbreviated to E.coli), a high-resolution image of which is shown in Author(s): 2.1 The problems of iron uptake Iron has a high natural abundance. It is the second most abundant metallic element by mass in the Earth's crust (7.1 per cent). What are the main oxidation states of iron? Learning outcomes By the end of this unit you should be able to: describe some of the biochemical methods by which organisms uptake iron; describe some of the biochemical processes by which organisms store and transfer iron; explain why iron is present only in very low concentrations in aqueous solution; use aspects of iron(III) chemistry to explain the role of macrocyclic ligands in iron uptake and transfer. 3.7 Selecting the sex of a child Once a pregnancy has been established, many couples are anxious to know the sex of their unborn baby. The reasons for this are many, ranging from the prosaic (will the baby be able to use its brother's or sister's old clothes) to the deeply religious (as described for Hindus in Section 2). In many communities there is so much social pressure on mothers to produce the ‘right’ sex (usually male) that infanticide of the ‘wrong’ sex is widely practised. Because this is illegal in most soc 3.5 A new life There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’, i.e. when a woman could feel her fetus moving inside her. However, both these opinions suffer from an underlying falsehood: that life ‘begins’ at all. Life is a continuum; gametes are produced by living parents, and fuse to produce new living individuals, but unfused gametes are n 4.6 Hormonal control of egg production As you can see from the preceeding section, hormones play a crucial role in the maturation of the oocyte. Figure 3 showed you how levels of oestogen and progestogen vary throughout the menstrual cycle, and suggested that hormone balance is important for a woman's fertility, but you can now see how subtle the control really is. Cells have to develop sensitivity to hormones at the times when the hormones are likely to be present, otherwise the entire operation will fail. 4.2 The reduction of chromosome number: meiosis If you look at the chromosomes shown in Figure 8 you will see that they have been lined up in pairs. The members of each pair are of similar shape and size, and unlike the members of other pairs. At a molecular level these distinctions are maintained: the order of the bases in the DNA is very similar in both members of a pair, but is quite different from that found in other pairs. By ‘very similar’ we mean that the order of the particular genes on each chromosome of the pair is the same, 4.1 Why are cells different? Now let us go on with our story and assume that we have decided the time is right to have a baby. The primary requirement for conception is that healthy gametes should be produced. We shall therefore look first at how gametes are made, and then examine some of the factors affecting their quality. But we must start with an explanation of what gametes are, and what sets them apart from other kinds of cell. In other words, what makes gametes special? Gametes are the cells that fuse to form a new 3.6 Summary of Section 3 Many people wish to limit the number of their offspring, and so resort to contraceptive measures. Chemical contraceptives interrupt the production of gametes, or prevent implantation. Mechanical or barrier contraceptives prevent egg and sperm from meeting and, in the case of IUDs, prevent implantation. Surgical methods of contraception involve physical alteration of the reproductive tract so as to prevent e
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Activity 1
