Importance of sickle cell gene against malaria

Importance of sickle cell gene against malaria
You have been studying genetic transmission and should be aware of law of dominance
in gene expression pattern.
Studies have shown that sometimes being a carrier for a certain disease is
advantageous over being affected or completely healthy for that gene. Sickle-cell
anemia (SCA) is an example of this kind of ‘heterozygote advantage’ in certain
populations.
SCA is a genetic blood disorder when hemoglobin has abnormal sickle shape.
Hemoglobin S (HbS) is a variant form of normal hemoglobin (HbA) gene and is very
common in Africa. Interestingly, heterozygotes for that gene (HbAS) are in positive
selection in those regions compared to homozygotes (HbSS) and are more protected
from malaria morbidity/mortality (see image)

Part I. Fill in the blanks (copy/paste the table in your reply)
Genetic make up of
individual
Characteristic of
individual
Outcome with no
malarial infection
Outcome with
malarial infection
HbAA No sickle cell trait Survives Dies young
HbAS Sickle cell trait Survives Low malaria
morbidity
HbSS Sickle cell trait survives High morbidity

Please describe some ways in which being a SCA carrier can be advantageous and
disadvantageous. What are some reasons why the SCA allele frequency is higher in Africa than
in America?
Advantages of an SCA carrier:
Since the individuals possess one SCA allele and one unaffected allele, they will not
experience certain diseases such as malaria and a greater chance of a surviving outbreak
(Stotesbury et al. 2018).
Disadvantages of an SCA carrier:
One of the major disadvantages of being SCA carrier is that the carriers may typically die
because of genetic disease. Hence, the individual with normal hemoglobin tends to pass their
genes successfully to next-generation compared to individuals with sickle cell anemia (Connes
et al. 2018).
The SCA allele frequency is higher in Africa than in
America:
The incidence of the sickle cell allele is highly prevalent in African populations compared
to African Americans and the American population is because of the fact that this selection and
the genetic mixing between whites and blacks in the United States (Connes et al. 2018).
Consequently, positive selection is highly prevalent in African compared to the American
population.

References:
Connes, P., Renoux, C., Romana, M., Abkarian, M., Joly, P., Martin, C., Hardy-Dessources, M.D.
and Ballas, S.K., 2018. Blood rheological abnormalities in sickle cell anemia. Clinical
hemorheology and microcirculation, 68(2-3), pp.165-172.
Stotesbury, H., Kirkham, F. J., Kölbel, M., Balfour, P., Clayden, J. D., Sahota, S., ... and Inusa, B.
2018. White matter integrity and processing speed in sickle cell anemia. Neurology, 90(23),
e2042-e2050.