Marisa DiBartolomeo
Bio 180 – sec. 05
September 11, 2013
Ch.8 Into The Jungle: “Sickle-Cell Safari”

Chapter Questions 1) How did Tony Allison’s early life experiences in Kenya prepare him to make the discovery of the sickle cell-malaria link? * As a young child, Tony Allison was interested in science. On school holiday’s Tony would take trips with a family friend to observe African birds and when he became a teenager, he had the opportunity to study artifacts of “Elmenteitan” culture. Unfortunately, when he was about ten years old, Tony Allison contracted malaria. While studying at Oxford University, Allison connected malaria with the location in which he contracted it. Through his knowledge of how malaria is contracted and the location of which he caught the disease, Allison was able to create a prediction about the location in which malaria is mostly contracted. Having the location and studying the blood of the people who lived in certain areas, he realized that people who have sickled blood cells are more likely to contract the disease. Also, Tony pieced together that there was a possibility that the HbS allele, in heterozygotes for sickle cell anemia, aided in some degree of resistance to malaria. Without his early life experience of being diagnosed with malaria and without his background knowledge of Africa, Tony Allison may have had a more difficult time trying to discover the connection between sickle cells and malaria.

2) What makes the sickle-cell mutation a balanced polymorphism? * The sickle cell mutation is an example of balanced polymorphism because the AS heterozygotes have an advantage over either SS homozygote. Allison discovered that 26% more of heterozygote children than homozygote children reached adulthood, but only about 1/3 of the homozygotes were able to reach adulthood. Carroll describes this selective advantage as “the largest selective advantages ever measured for any trait in any species. (160)”

3) Why was the demonstration of human resistance to malaria important to evolutionary biology? * The demonstration of human resistance to malaria is important to evolutionary biology because the degree of resistance is measurable and important in early life. Allison’s discovery is unique because it is an example of a mutation that may be beneficial instead of the stereotypical view that all mutations are harmful. Although the HbS mutation is typically harmful, certain cases, such as this sickle cell-malaria link, prove that the HbS mutation may be helpful.