Key Stage 4 What makes a good model organism? Model Organisms in Research Make a list of qualities that you think might make a good model organism for research. Student worksheet Your task:

Why use Model Organisms? For the research into hardy crops covered in the animation, use the information provided to write a short paragraph evaluating Many important research questions require us to understand their choice of Arabidopsis as a model organism. how organisms function. In the video you have just watched, understanding how a single protein (SP1) functions may allow us to increase our agricultural output significantly and so help 1. For each of the following research scenarios pick the top prevent potential future food security issues. Such 3 best model organisms to use. For each, write a short understanding is difficult to achieve. This is particularly the case paragraph to explain your decision. for complex organisms in which there are many intricate interactions between cells and between biological molecules. a. Scientists assessing the role of a protein in human embryo development. Currently scientists know Such complexities can make it difficult for scientists to reach that this protein is present but do not know its meaningful conclusions when conducting experiments in vivo (as role. it can make it difficult to know exactly which factor is causing an b. Scientists carrying out multigenerational study on observed result). Thus, scientists will often study comparatively the effects of increased UV radiation on the ‘simple’ model organisms. functioning of the nervous system. c. A study into the effect of a new drug thought to A wide range of study organisms are used increase the numbers of phagocytes in the blood. in science and there are a number of Scientists want assess the wider effects of the biological, ethical and logistical concerns drug on the immune system. that scientists must consider before choosing their model organism. You will consider some of these in the coming activity.

www.oxfordsparks.ox.ac.uk/content/hardy-crops-tackle-food-insecurity Arabidopsis thaliana (Mouse-ear cress) humans and nematodes have a very similar structure, both being myelinated and controlled by neurotransmitters. Arabidopsis is a small flowering plant that grows commonly in Europe and North Africa. To many it C. elegans was the very first multicellular organism to have its is considered a weed as it has little or no whole genome published in 1998, and the fate of each of its 959 commercial value. It is, however, closely related to a number of somatic (non-reproductive cells) have been mapped. This means commercial plants including the broccoli and cauliflower, and that each cell division during its embryonic and adult shares the vast majority of its biochemistry with other plants, development is known and so the consequence of any change in including commercially grown crops and trees. development can be noticed. While a much simpler system than human development, many of the chemicals and processes Arabidopsis is easy to grow in the lab and proliferates very involved are the same in both species. In addition, C. elegans is quickly, taking only three months to go from germination to also transparent which makes visualising abnormalities easy. seed production. Each plant will produce many seeds and so it is easy for scientists to grow and maintain large sample sizes. The C. elegans provides a very simple study organism, yet, at a plant also has a comparatively small genome of only 135 million genetic level, humans have many genetic counterparts to the base pairs organised into 5 chromosome pairs (human genome genes found in these nematodes. is 3 billion base pairs and consists of 23 chromosome pairs). Arabidopsis was also the first plant to have its genome Their simplicity makes them very cheap and easy to keep in a sequenced in the year 2000 and many of the functions of its laboratory setting and they proliferate quickly; producing about 25,000 genes have now been characterised. Our knowledge of 1000 eggs a day and living for only a few weeks. its genome, and its relative simplicity make genetic studies Mus musculus (Mouse) comparably easy. Mice are small mammals with a large number

of genetic, physiological, biochemical and Caenorhabditis elegans (Nematode worm) anatomical similarities to humans. C. elegans are found free living in the soil and are While complex organisms, mice are relatively cheap and easy to about 1mm long, transparent and hermaphrodites. look after in a laboratory setting. Mice also breed very quickly While a multicellular animal, it has few of the (about 10 weeks after birth) meaning mutant strains can be complex organs/systems associated with humans developed quickly. and other mammals such as a heart, lungs, circulatory and digestive systems. Despite this, nerves in both www.oxfordsparks.ox.ac.uk/content/hardy-crops-tackle-food-insecurity The complete mouse genome sequence was published in 2002 Drosophila melanogaster (Fruit fly) and it shares many genes with humans. For a complex organism, Drosophila is a small fly only a couple of mm in the mouse genome is relatively easy to manipulate. Thus, many length. It develops very quickly and has a short ‘strains’ of mice have been bred. For example, strains of mice generational time (about 10 days). Females lay about 50 eggs a have been bred that lack a functioning immune system or which day and they are very cheap and easy to care for in large are prone to developing diabetes. numbers. This means that huge numbers of drosophila can be As vertebrates, mice are given a high degree of ethical used in studies to create large sample sizes. protection and researchers must gain stringent ethical Despite vastly different physiologies, Drosophila share permissions before commencing research. significant genetic similarities with humans. Indeed, Drosophila Danio rerio (Zebra fish) and humans are estimated to share 60% of genes, and three quarters of human disease-associated genes have equivalents in The zebra fish is a small fish native to Drosophila. South East Asia. As vertebrates, they have a large degree of genetic similarity to humans (84% of The 139 million base pair genome of Drosophila was fully categorised human disease-causing genes have counterparts in sequenced in 2015. Under lab conditions it is easy to induce zebrafish). The zebrafish genome (1.5 billion base pairs long) mutations in the Drosophila genome and there are a number of was fully sequenced and published in 2013. Zebrafish also share well-known and easily identifiable mutations that make genetic many anatomic/physiological similarities with humans including studies straightforward. The most famous of these are the white muscle, blood, kidneys and eyes. eye and vestigial wing mutations.

Zebrafish are transparent during their early stages of Macaca mulatta (Rhesus macaque) development. This early period of transparency allows scientists The rhesus macaque is a primate native to South to directly observe aspects of their early embryonic and South East Asia. It is described as least development. Zebrafish also mature quickly and produce threatened on the IUCN red list and while relatively offspring rapidly. As small fish, they are cheap to maintain and expensive to keep and maintain compared to other care for in large numbers. study organisms, it is easier than other primates. As a primate the rhesus macaque is very closely related to humans, last sharing a common ancestor only 25 million years ago (a very short time on an evolutionary scale). Its 3 billion base pair www.oxfordsparks.ox.ac.uk/content/hardy-crops-tackle-food-insecurity genome was sequenced in 2007 and analysis indicates that rhesus macaques share 93% of our DNA sequence!

The rhesus macaque also has significant anatomical, developmental and physiological similarities to humans. As well as almost identical organ structure and arrangement, the rhesus macaque carries out many biochemical processes and developmental processes in the same way. Importantly, the rhesus macaque has a well-developed (and highly similar) nervous and immune systems. Such is the similarity to humans, both NASA and the Russian space agencies have used these monkeys in space missions prior to launching human astronauts.

Given their developed nervous systems, the highest levels of ethical consent must be granted before any research can commence. Granting of ethical consent depends on the potential value of the research being undertaken, the nature of the research and the treatment of the study organisms.

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