The continued occurrence of sickle-cell disease with malaria...

The continued occurrence of sickle-cell disease with malaria in
parts of Africa is due to
a. continual mutation.
b. gene flow between populations.
c. relative fitness of the heterozygote
d. disruptive selection.
e. protozoan resistance to DDT.

Key Concepts

Balancing Selection

Balancing selection is a form of natural selection that preserves multiple alleles in a population. It can arise through mechanisms such as heterozygote advantage, where the presence of diverse alleles has a beneficial effect on survival and reproduction, preventing any single allele from becoming fixed.

Natural Selection

Natural selection is the process by which traits that improve survival and reproduction become more common in a population over successive generations. It serves as the driving force behind evolution by favoring individuals whose genetic traits allow them to cope better with environmental challenges.

Heterozygote Advantage

Heterozygote advantage, also known as overdominance, occurs when individuals carrying two different alleles for a specific gene have a higher fitness compared to those with two copies of the same allele. This advantage can maintain both alleles in the population, contributing to the persistence of genetic diversity.

Transcript

00:01 Action asks why there is a continued occurrence of the sickle cell disease with malaria in parts of africa.

00:09 So basically, if we see a map of africa right here, these areas, which are very prevalent with malaria, have a higher frequency of the sickle cell allele.

00:22 So the sickle cell allele is what causes a deformation in blood cells and can cause anemia.

00:30 But the seemingly detrimental allele is present in much higher frequencies in areas with greater exposure to malaria.

00:41 So if we think about why this is a case, i will show you here the sickle cell allele is characterized by the recessive small a.

00:54 So if we see here, this is just a normal human being with normal blood cells, no different deformed red blood cells.

01:04 So they are actually more susceptible to malaria than those who are either heterozygous or homozygous recessive.

01:13 And that is because when these red blood cells are deformed, it is harder for the parasite that causes malaria to infect.

01:24 The red blood cells because they are deformed.

01:27 So the reason for the continued persistence of small a, so the sickle cell allele in african populations that are greatly exposed to malaria, is that it provides a certain form of defense against this parasite.

01:50 So while it's not good to be actually homozygous recessive, because then you have fatal sickle cell disease, it is beneficial to actually be heterozygous.

01:59 So you are resistant to malaria because you have enough of these deformed red blood cells to provide immunity against malaria, but also then you only have mild sickle cell disease.

02:13 So if we go down the options that basically with some of the reasons, a says continual mutation...

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