Describe how transgenic plants can be cloned

Surface of explants of transgenic plants are sterilized using dilute sodium hypochlorite and are aseptically transferred to culture vessels containing nutrients and plant growth regulators.
Cytokinin is added to nutrient agar to stimulate the cells of explant to divide by mitosis forming a callus and these cells are induced to proliferate into particular tissues by varying the combination of the various plant growth regulators.
The number of calli increased by subculturing and the cells of the callus are induced by auxin and giberellin to differentiate into particular tissues.
When these tissues developed into a plantlet and become suffieciently large, it is transferred from a laboratory to the soil and grown into a whole plant.

What is Huntington's Disease?
Huntington's disease (HD) results from genetically programmed degeneration of brain cells, called neurons, in certain areas of the brain. This degeneration causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance. HD is a familial disease, passed from parent to child through a mutation in the normal gene. Each child of an HD parent has a 50-50 chance of inheriting the HD gene. If a child does not inherit the HD gene, he or she will not develop the disease and cannot pass it to subsequent generations. A person who inherits the HD gene will sooner or later develop the disease. Whether one child inherits the gene has no bearing on whether others will or will not inherit the gene. Some early symptoms of HD are mood swings, depression, irritability or trouble driving, learning new things, remembering a fact, or making a decision. As the disease progresses, concentration on intellectual tasks becomes increasingly difficult and the patient may have difficulty feeding himself or herself and swallowing. The rate of disease progression and the age of onset vary from person to person. A genetic test, coupled with a complete medical history and neurological and laboratory tests, helps physicians diagnose HD. Presymptomic testing is available for individuals who are at risk for carrying the HD gene. In 1 to 3 percent of individuals with HD, no family history of HD can be found.

Is there any treatment?

Physicians prescribe a number of medications to help control emotional and movement problems associated with HD. Most drugs used to treat the symptoms of HD have side effects such as fatigue, restlessness, or hyperexcitability. It is extremely important for people with HD to maintain physical fitness as much as possible, as individuals who exercise and keep active tend to do better than those who do not.

What is the prognosis?

At this time, there is no way to stop or reverse the course of HD. Now that the HD gene has been located, investigators are continuing to study the HD gene with an eye toward understanding how it cause disease in the human body.

What research is being done?

Scientific investigations using electronic and other technologies enable scientists to see what the defective gene does to various structures in the brain and how it affects the body's chemistry and metabolism. Laboratory animals are being bred in the hope of duplicating the clinical features of HD so that researchers can learn more about the symptoms and progression of HD. Investigators are implanting fetal tissue in rodents and nonhuman primates with the hope of understanding, restoring, or replacing functions typically lost by neuronal degeneration in individuals with HD. Related areas of investigation include excitotoxicity (overstimulation of cells by natural chemicals found in the brain), defective energy metabolism (a defect in the mitochondria), oxidative stress (normal metabolic activity in the brain that produces toxic compounds called free radicals), tropic factors (natural chemical substances found in the human body that may protect against cell death).


Dominant autosomal allele
42-100 repeats of CAG
Chance of passing on the allele is 50%. 1 in 2 children would suffer from HD if 1 parent with heterozygous dominant gene is affected

Discuss the view that fiscal policy is the best method to promote economic growth in Singapore

Fiscal Policy

Fiscal policy is 1 of the 2 instruments of macroeconomic policy. It comprises public spending and taxation(including tax breaks to the private sector). The goal of fiscal policy is to influence the level of demand in the economy, with the twin goals of getting unemployment as low as possible without triggering excess inflation

Fiscal policy in Singapore is directed primarily at promoting long-term economic growth, rather than cyclical adjustment or distributing income. To meet its objective, the Singapore Government is guided by the following principles in its conduct of fiscal policy in Singapore:

i. the private sector is the engine of growth, and the government's role is to provide a stable and conducive environment for the private sector to thrive;

ii. tax and expenditure policies should be justified on microeconomic grounds and focus on supply-side issues, i.e. incentives for saving, investment and enterprise;

iii. the counter-cyclical role of fiscal policy is limited, due to high import leakages.

The success of Singapore's fiscal policy over the years lies in the government's prudent expenditure patterns and conducive taxation policies that have complemented monetary policy in promoting sustained and non-inflationary economic growth.

The main focus of the Government's expenditure is on the delivery of essential public goods and services to Singaporeans. The government spends to assure the nation of a secure future. Therefore, key areas of expenditure are on education, public housing, health care and national security. The Government is also committed to building and maintaining world-class economic infrastructure and services. This is evidenced by the fact that development expenditure accounted for around one-third of government expenditure on average over the last three decades.

Singapore's tax policies, although providing the main source of funding for the government, seek to enhance its economic competitiveness and attract foreign investments to Singapore.

This combination of fair tax policies and prudent expenditure programmes, augmented by high economic growth has enabled Singapore to enjoy consistent budget surpluses over the years. Such a prudent fiscal policy has also contributed to Singapore's high savings rate and allows it to achieve one of the highest investment rates in the world without having to incur foreign debt. High domestic savings have, in turn, contributed to Singapore's high level of foreign reserves, which has served to boost investor confidence and provided a buffer against adverse economic shocks.

With this ethos of fiscal rectitude, which extends throughout the public sector, the MAS has been able to focus on its primary goal of ensuring price stability and preserving confidence in the domestic currency through the appropriate management of the S$ exchange rate, without needing to balance this against the requirements of deficit financing.

The key objective of Singapore's monetary policy is to maintain price stability for sustained economic growth. Since 1981, monetary policy in Singapore has been centred on the exchange rate. This reflects the fact that in the small and open Singapore economy where imports and exports amount to more than twice GDP, the exchange rate is the most effective tool in controlling inflation.

The MAS manages the Singapore dollar (S$) exchange rate against a trade-weighted basket of currencies of Singapore's major trading partners and competitors. The composition of this basket is reviewed and revised periodically to take into account changes in Singapore's trade patterns. This trade-weighted exchange rate is maintained broadly within an undisclosed target band, and is allowed to appreciate or depreciate depending on factors such as the level of world inflation and domestic price pressures. MAS may also intervene in the foreign exchange market to prevent excessive fluctuations in the S$ exchange rate.

Monetary policy is reviewed on a semi-annual basis to ensure that it is consistent with economic fundamentals and market conditions, thereby ensuring low inflation for sustained economic growth over the medium term. The MAS publishes a semi-annual Monetary Policy Statement (MPS) in April and October which explains its assessment of Singapore's economic and inflationary conditions and outlook, and sets out its monetary policy stance for the following six months. Singapore's exchange rate-based monetary policy system and its experience since its adoption are reviewed in MAS' monograph on Singapore's Exchange Rate Policy .

In the context of Singapore's open capital account, the choice of the exchange rate as the focus of monetary policy would necessarily imply that domestic interest rates and money supply are endogenous. As such, MAS' money market operations are conducted mainly to ensure that sufficient liquidity is present in the banking system to meet banks' demand for reserve and settlement balances. The key aspects of MAS' monetary policy operations, viz. foreign exchange and money market operations, and the various factors and considerations underlying them, are discussed in MAS' monograph on Monetary Policy Operations in Singapore .

Stem Cells

Describe and explain the unique features of Stem Cells
[6 marks]

Stem Cells are unspecialized as there is an absence of tissue-specific structures that allow it to perform specialized functions.

Stem cells are capable of continually renewing and dividing through cell division for long periods, stem cells are able to proliferate and replicate many times unlike normal cells.

Stem cells are capable of differentiating into specialized cell types under appropriate conditions.

Stem cells undergo differentiation when triggered by intracellular and extracellular signals. The intracellular signals are controlled by the cell's genes which are interspersed along long strands of DNA, which carries coded instructions for all the structures and functions of a cell.

The extracellular signals are chemicals secreted by other cells, physical contact with neighbouring cell and certain molecules and compunds surrounding a cell in an organism.

From the National Institute of Health:

What are stem cells and why are they important?

Stem cells have two important characteristics that distinguish them from other types of cells. First, they are unspecialized cells that renew themselves for long periods through cell division. The second is that under certain physiologic or experimental conditions, they can be induced to become cells with special functions such as the beating cells of the heart muscle or the insulin-producing cells of the pancreas.

Scientists primarily work with two kinds of stem cells from animals and humans: embryonic stem cells and adult stem cells, which have different functions and characteristics that will be explained in this document. Scientists discovered ways to obtain or derive stem cells from early mouse embryos more than 20 years ago. Many years of detailed study of the biology of mouse stem cells led to the discovery, in 1998, of how to isolate stem cells from human embryos and grow the cells in the laboratory. These are called human embryonic stem cells. The embryos used in these studies were created for infertility purposes through in vitro fertilization procedures and when they were no longer needed for that purpose, they were donated for research with the informed consent of the donor.

Stem cells are important for living organisms for many reasons. In the 3- to 5-day-old embryo, called a blastocyst, stem cells in developing tissues give rise to the multiple specialized cell types that make up the heart, lung, skin, and other tissues. In some adult tissues, such as bone marrow, muscle, and brain, discrete populations of adult stem cells generate replacements for cells that are lost through normal wear and tear, injury, or disease.

It has been hypothesized by scientists that stem cells may, at some point in the future, become the basis for treating diseases such as Parkinson's disease, diabetes, and heart disease.

Scientists want to study stem cells in the laboratory so they can learn about their essential properties and what makes them different from specialized cell types. As scientists learn more about stem cells, it may become possible to use the cells not just in cell-based therapies, but also for screening new drugs and toxins and understanding birth defects. However, as mentioned above, human embryonic stem cells have only been studied since 1998. Therefore, in order to develop such treatments scientists are intensively studying the fundamental properties of stem cells, which include:

1. determining precisely how stem cells remain unspecialized and self renewing for many years; and
2. identifying the signals that cause stem cells to become specialized cells.

II. What are the unique properties of all stem cells?

Stem cells differ from other kinds of cells in the body. All stem cells—regardless of their source—have three general properties: they are capable of dividing and renewing themselves for long periods; they are unspecialized; and they can give rise to specialized cell types.

Scientists are trying to understand two fundamental properties of stem cells that relate to their long-term self-renewal:

1. why can embryonic stem cells proliferate for a year or more in the laboratory without differentiating, but most adult stem cells cannot; and
2. what are the factors in living organisms that normally regulate stem cell proliferation and self-renewal?

Discovering the answers to these questions may make it possible to understand how cell proliferation is regulated during normal embryonic development or during the abnormal cell division that leads to cancer. Importantly, such information would enable scientists to grow embryonic and adult stem cells more efficiently in the laboratory.

Stem cells are unspecialized. One of the fundamental properties of a stem cell is that it does not have any tissue-specific structures that allow it to perform specialized functions. However, unspecialized stem cells can give rise to specialized cells, including heart muscle cells, blood cells, or nerve cells.

Stem cells are capable of dividing and renewing themselves for long periods. stem cells may replicate many times by proliferation. A starting population of stem cells that proliferates for many months in the laboratory can yield millions of cells. If the resulting cells continue to be unspecialized, like the parent stem cells, the cells are said to be capable of long-term self-renewal.

The specific factors and conditions that allow stem cells to remain unspecialized are of great interest to scientists. It has taken scientists many years of trial and error to learn to grow stem cells in the laboratory without them spontaneously differentiating into specific cell types. For example, it took 20 years to learn how to grow human embryonic stem cells in the laboratory following the development of conditions for growing mouse stem cells. Therefore, an important area of research is understanding the signals in a mature organism that cause a stem cell population to proliferate and remain unspecialized until the cells are needed for repair of a specific tissue. Such information is critical for scientists to be able to grow large numbers of unspecialized stem cells in the laboratory for further experimentation.

Stem cells can give rise to specialized cellsby differentiation. Scientists are just beginning to understand the signals inside and outside cells that trigger stem cell differentiation. The internal signals are controlled by a cell's genes, which are interspersed across long strands of DNA, and carry coded instructions for all the structures and functions of a cell. The external signals for cell differentiation include chemicals secreted by other cells, physical contact with neighboring cells, and certain molecules in the microenvironment.

Therefore, many questions about stem cell differentiation remain. For example, are the internal and external signals for cell differentiation similar for all kinds of stem cells? Can specific sets of signals be identified that promote differentiation into specific cell types? Addressing these questions is critical because the answers may lead scientists to find new ways of controlling stem cell differentiation in the laboratory, thereby growing cells or tissues that can be used for specific purposes including cell-based therapies.

Adult stem cells typically generate the cell types of the tissue in which they reside. A blood-forming adult stem cell in the bone marrow, for example, normally gives rise to the many types of blood cells such as red blood cells, white blood cells and platelets. Until recently, it had been thought that a blood-forming cell in the bone marrow—which is called a hematopoietic stem cell—could not give rise to the cells of a very different tissue, such as nerve cells in the brain. However, a number of experiments over the last several years have raised the possibility that stem cells from one tissue may be able to give rise to cell types of a completely different tissue, a phenomenon known as plasticity. Examples of such plasticity include blood cells becoming neurons, liver cells that can be made to produce insulin, and hematopoietic stem cells that can develop into heart muscle. Therefore, exploring the possibility of using adult stem cells for cell-based therapies has become a very active area of investigation by researchers.