Name:
A107 Lab 2 – Natural Selection in Humans
As you watched in the video, a mutation in the DNA causes an important change
in the structure of hemoglobin, which then causes red blood cells throughout the
body to collapse into sickle-shapes instead of rounded discs. If enough red blood
cells (RBCs) in the body sickle, this can lead to the life-threatening disease called
sickle-cell anemia.
Sickle cell alleles are co-dominant. This means that the Aa genotyped offspring
have both kinds of hemoglobin: half normal, half mutated. They are called
carriers.
You can watch the video again here (source: HHMI biointeractive):
https://www.youtube.com/watch?v=Zsbhvl2nVNE
1. In the Punnett Square below, both parents are carriers of the sickle cell allele, a.
a) What percentage of their offspring will also be carrier? [5 points]
b) What percentage of their offspring will have normal RBCs? [5 points]
c) What percentage will have entirely mutated hemoglobin, i.e., will have sickle cell anemia?
[5 points]
2. Is malaria a genetically inherited disease? Explain briefly. [10 points]
3. Is sickle cell anemia a genetically inherited disease? Explain briefly. [10 points]
4. What will likely happen to the following persons in an area where malaria is very common, and no
treatments or other anti-malarials exist:
a) A person with the AA genotype? [10 points]
b) A person with the aa genotype? [10 points]
c) A carrier (Aa)? [10 points]
5. Which allele would you expect to increase in frequency (become more common) in East Africa if
the following situations occurred:
a) A cure for sickle cell anemia is discovered [5 points]:
b) A super effective malaria vaccine was widely distributed in the region [5 points]:
c) A massive migration of refugees from Northern Africa moved to East Africa [5 points]:
6. Malaria does not currently exist in Sweden. Imagine that a refugee population from East Africa has
just been invited to settle there permanently, and that the newcomers include some carriers of the
sickle cell allele. Over time you would expect (Circle one) [5 points]:
a) The allele to become less frequent in each generation
b) Aa (heterozygotes) genotypes to have more surviving children than AA and aa
(homozygotes)
c) The sickle cell allele to spread in the Swedish population
d) The death rates from malaria in Sweden to quickly increase
7. Explain in your own words why this is an example of Natural Selection in humans. You must refer to
the following key terms: adaptation, environment, and fitness. If needed, use your notes from class
to refresh your memory. [15 points]