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African Mystery !! by Suresh Nadarajan, Senthil Kumar and Benard Drogba looked at his younger brother with sadness. Drogba’s three year old brother Mugabe, was admitted at the village hospital in Angola, Africa. Mugabe was a cheerful toddler and was always playing with stones and pebbles while his father and mother were working in the tapioca plantation. Three days ago, Mugabe fell sick and had fever. Initially, his mother Jane was not worried as many children got sick in the village with fever. However, last night she was talking to her neighbour. “Where is your son, Mugabe?” quizzed her neighbour. “He has been sick the past few days. Fever.” replied Jane. “My cousins’ daughter was also suffering from fever and she was vomiting. She is now in hospital and is very critically ill. The doctor is trying to save her.” her neighbour mentioned with pity and concern. Late in the night, his fever got worse and his started vomiting. In the past few weeks, there was a malaria outbreak in the village. Many people especially the young and old have died. The village authorities were very busy spraying insecticides on the walls of the homes. Drogba however was a sickly child and often stayed at home. Drogba was weak and pale all the time. He was always short of breath whenever he goes out to play for a few minutes. He will often faint outside and his parents did not allow him to play outside. His mother used to say, “Drogba, you were perfectly fine when you were a baby. However, as you grew older you started to cry in pain at night. You were often short of breath and pale. You are a special gift to us, Drogba !” . Drogba was diagnosed to be a carrier of the sickle cell disease. Fig. 1 Malaria cases per 100,000 Fig.2 Malaria deaths per 100,000 Fig. 3 Malarial deaths per 100 000 Fig. 4 Prevalence of HbS allele frequency Fig. 5 Global Malaria Endemicity Resources http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3060623/pdf/ncomms1104.pdf pHET: natural selection http://sasi.group.shef.ac.uk/worldmapper/display.php?selected=230 http://sasi.group.shef.ac.uk/worldmapper/display.php?selected=229 GapMinder: malaria deaths per 100,000 Activities: Where is malaria distributed in the world? Why Mugabe in hospital while Drogba is perfectly fine? Products: Lab report, presentation, poster in small group settings Rubric: http://sciencecasenet.org/wp-content/uploads/2013/03/JC-10-RubricCollaboration-2.doc H2 Syllabus alignment Genetic Basis for Variation (a) Explain the terms, locus, allele, dominant, recessive, codominant, homozygous, heterozygous, phenotype and genotype. (b) Explain how genotype is linked to phenotype and how genes are inherited from one generation to the next via the germ cells or gametes. (c) Explain, with examples, how the environment may affect the phenotype Diversity and Evolution (e) Explain why variation is important in selection. (f) Explain, with examples, how environmental factors act as forces of natural selection. 21st Century Competencies Global Awareness Critical and Inventive Thinking Information and Communication Skills Teacher’s Note : Heterozygote advantage: Malaria-rich areas Places with a high incidence of malaria e.g. West Africa also have high frequency of the HbS allele. Heterozygote individuals (HbAHbS) are at selective advantage in areas where malaria is common. They are less susceptible to malaria than individuals who lack the HbS allele This is because the parasite spends part of its life cycle in the red blood cell. So the parasite is less able to survive in red blood cells with haemoglobin S Yet heterozygotes are phenotypically similar to individuals homozygous for the normal allele. They exhibit the sickle cell trait Their red blood cells sickle only when oxygen concentration in the blood is low. Such a condition is known as heterozygote advantage. The heterozygote is fitter than either of the two homozygotes. It is because of heterozygote advantage that both alleles (HbS and HBA) persist in populations today.