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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
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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:
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Where is malaria distributed in the world?
Why Mugabe in hospital while Drogba is perfectly fine?
Products:
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Lab report, presentation, poster in small group settings
Rubric:
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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
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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.
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Such a condition is known as heterozygote advantage.
 The heterozygote is fitter than either of the two homozygotes.
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It is because of heterozygote advantage that both alleles (HbS and HBA) persist in
populations today.