page 2 page 3 Teacher's Notes Mechanisms of Evolution Grades: 11-12 Duration: 28 mins Summary of Program Evolution is the gradual change that can be seen in a population s genetic composition, from one generation to the next. The three main mechanisms of evolution include: 1. Genetic Drift 2. Mutation, and 3. Natural Selection The first part will concentrate on Genetic Drift with the use of a model to demonstrate its effect on small and large populations. An example will also be used to explain how Genetic Drift can lead to the formation of new biological species over a long period of time. Then models of Mutation and Natural Selection will be demonstrated and the results carefully tabulated and analyzed. Examples of particular populations, which have likely evolved through each mechanism, will also be highlighted. 1. Genetic Drift A population is a group of interbreeding organisms of the same species. There is great variation within any population due to each type of gene being present in different forms and frequencies. The collection of all the different types of genes in a population is known as a gene pool. From generation to generation, changes in the gene pool will occur due to chance leading to the disappearance of particular forms of a gene. This phenomenon is called Genetic Drift and it occurs more quickly when the population is small. Since this process is due to chance, the loss of a particular gene from a population s gene pool is completely random. This means that two different populations of a certain species living in close proximity yet isolated from each other (e.g.. geographical barrier) may produce different results. The long-term outcome of Genetic Drift occurring in these two populations can be the formation of a new biological species. This is known as speciation. 2. Mutation Mutations are changes that can occur in individuals DNA. They may result from a deletion, transposition or duplication of a part of the DNA, or a substitution of one or more nucleotides in the molecule. Most mutations occur randomly and spontaneously, and generally have no effect on the organism s survival. However, other types of mutations include those that are: a) deleterious, which have a varying, negative effect on an organism s survival b) lethal, where organism s do not live long enough to reproduce, and c) advantageous, which increases the organism s chances of survival. Mutations are generally regarded as the main driving force for evolutionary change. 3. Natural Selection In any organism a particular gene will occur in pairs (one from each parent) called alleles. Alleles may confer favourable characteristics to the organism making it more likely to survive and reproduce in a particular environment. This means that these alleles are more likely to be present in greater numbers in the next generation. In contrast, an organism that has inherited less favourable alleles for a particular environment will be less likely to survive and reproduce. These alleles
page 4 page 5 page 6 will eventually diminish from the population with time. This interaction between an organism and its environment results in changes in the population s gene pool from generation to generation, leading to evolution. This process was introduced by Charles Darwin in 1838 and is known as Natural Selection. Humans have been manipulating the process of selecting favourable characteristics for the purpose of breeding crops and animals. For example, traits for sweetness in fruit and size in animals are often specifically selected and carefully bred into succeeding generations. This is called artificial selection. The smaller the population size, the quicker the desired outcome is reached. Pre-Video Work 1. Students can write their own definition for what they understand evolution to mean. Collect a variety of responses from the students and use them to formulate a formal definition for the class to incorporate into their work. 2. Visit the library with your class and instruct students to research two contributors to the theory of evolution and briefly describe their ideas (e.g.. Charles Darwin, Jean Baptiste Lamarck, Georges Cuvier, Louis Agassiz, Alfred Russel Wallace). 3. Have a Pop Quiz with the class or simply discuss the meaning of the following terms, population, genes, gene pool, and species. 4. Read the questions on the student work sheet with the class to familiarize them with the work to be completed. It is advised that students carefully view the video first to give it their full attention and then attempt the questions during a second viewing. 5. Revise work on mutations by discussing the following terms, chromosome, gene, allele, DNA, nucleotide, base pair, amino acid, mutation, DNA replication, and protein synthesis (transcription and translation). Alternatively, students could be asked to write a paragraph about mutations using the above terms. 6. Visit the library to research diseases/disorders caused by different types of mutations. Students could either a) be given the name of a particular condition to work on and be asked to determine the category of mutation that it belongs to along with its effects on the individual and possible treatment, or else, b) choose their own disorder to research from a pre-determined category. This will eliminate students all researching the same disease. A brief presentation could then be given to the class. Conditions could include sickle cell anaemia, phenylketonuria, Down s Syndrome, haemophilia, Tay-Sachs disease, Huntington s disease, colour-blindness, Duchenne muscular dystrophy, Aniridia tumour, Wilms tumour, dwarfism, albinism. 7. Ask students to write a paragraph about the main idea behind Natural Selection. Students are encouraged to discuss their understanding of Natural Selection with the class.
CREDITS Writer/Producer Arthur Tanaka On-line Editor Dominique Fusy Photography Peter Beeh Graphics/Editor Rowena Crowe Sound Phillip Mcguire Dominique Fusy Consultant/Teachers Notes Vanesssa Hutchinson Executive Producers John Davis Corinna Klupiec Thanks to Mark Tanaka University of NSW Copyright CLASSROOM VIDEO (2004) and Orders: Classroom Video 107 1500 Hartley Avenue Coquitlam, BC V3K 7A1 Ph: (604) 523 6677 Fax: (604) 523 6688 email: sales@classroomvideo.com Australia: Phone: (02) 9913 8700 Fax: (02) 9913 8077 UK: Phone: (01454) 324222 Fax: (01454)325222 USA: Phone: 800 665 4121 Fax: 800 665 2909 New Zealand Phone/Fax: (09) 478 4540
Student Worksheet: Part 1 - Genetic Drift 1. What is heredity? 2. Who described how heredity works? 3. What word did he use for the term gene? 4. How do bacteria and eukaryotes differ? 5. What is an allele? 6. How did the two students in the demonstration ensure random mating would occur between the organisms they were studying? 7. What assumptions are made in this demonstration? 8. Describe the results obtained from this demonstration? 9. Describe a population bottleneck. 10. Where can population bottlenecks occur in nature? 11. What happened when the demonstration was repeated with a larger population? 12. How is Genetic Drift used a genetic tool? 13. Define speciation and how it can occur. 14. Why does Madagascar have so many different varieties of Lemurs? 15. Genetic Drift occurs in small populations and in larger populations. 16. Genetic Drift occurs in isolated populations and in non-isolated populations. 17. Populations living close to each other, but isolated from each other may drift into becoming species over a very long time, through Genetic Drift. Activities following the video 1. Students can repeat the experiments for themselves. Half the class can examine the effect of Genetic Drift on large populations and the other half, small populations. Between each group comparisons can be made about which genes have gone extinct. This can highlight the random nature of Genetic Drift. 2. Have students discuss in terms of Genetic Drift how it could be possible in nature for two different populations of the same species living close by to diverge into two different species over time. Discussion can be guided towards the effects of different types of isolation (eg. reproductive isolation, geographical isolation, genetic isolation). Research Task 1. In this video, two members of the Prosimian group of Primates, the Lemur s of Madagascar and the Lorises of India, were used as an example of populations that have experienced Genetic Drift. Use secondary sources to research another species that has undergone this process.
Student Worksheet: Part 2 - Mutation and Natural Selection 1. Define mutation. 2. Give an example of the effect of mutation. 3. Name 4 types of mutations. 4. A mutation has no effect on the survival of the organism. 5. The number of mutations far outweigh the, or mutations in any single organism. 6. Mutation is the ultimate source of genetic. 7. Evolution needs. 8. Mutation acts in opposition to by increasing variation. 9. Name the organism that Darwin studied on the Galapagos Islands. 10. It is through Natural Selection that changes occur in a population. 11. Selection occurs when one is favoured over another by the environment. 12. Define adaptation. 13. How was Natural Selection modelled in the demonstration. 14. In a population, the effect of Natural Selection may take a long time to manifest. 15. In a small population what force can overpower the effect of Natural Selection? 16. What effect has Natural Selection had on fish and the fishing industry? 17. What effect has Natural Selection had on bacteria? 18. How have humans used Natural Selection to their advantage? Give examples of its use. Activities following the video 1. Students can design and conduct their own demonstration to model Natural Selection. It may involve using counters of varying colours of which one may be better able to camouflage into a particular surface (eg. the grass, earth or if you wish to remain in the classroom a coloured mat could be used). 2. Discuss the effects that Genetic Drift, Mutation and Natural Selection have on genetic variation. Students can also discuss the benefits of variation within a population. Research Task 1. In this video, the decrease in the size of fish caught by the fishing industry and the increased resistance of bacteria to antibiotics, were discussed as examples of Natural Selection. Students are to use secondary sources to research their own example of the effect of Natural Selection upon a population. Students may work in pairs to collect and present their information to the class.