Sickle Cell Anemia and Selection

The video tutorial discusses various patterns of natural selection, including directional, stabilizing, and disruptive selection. It explains how disruptive selection favors two distinct phenotypes in heterogeneous environments, using grass exposed to heavy metal as an example. The concept of balancing selection is introduced, highlighting the heterozygote advantage in sickle cell anemia and its relation to malaria. Negative frequency dependent selection is also covered, illustrating how rare traits can confer advantages that diminish as they become more common.

What is directional selection?

• Favoring an intermediate phenotype

• Favoring an extreme phenotype

• Favoring two different phenotypes

• Maintaining genetic diversity

In what type of environment does disruptive selection typically occur?

• Extreme environment

• Stable environment

• Heterogeneous environment

• Uniform environment

What is the main characteristic of balancing selection?

• It reduces genetic diversity

• It eliminates negative alleles

• It maintains genetic diversity

• It favors extreme phenotypes

How does the heterozygote advantage affect sickle cell anemia allele frequency?

• It has no effect

• It decreases the frequency

• It eliminates the allele

• It maintains a higher frequency

What is the relationship between sickle cell anemia and malaria?

• Sickle cell anemia increases susceptibility to malaria

• Sickle cell anemia provides no advantage against malaria

• Heterozygotes have an advantage against malaria

• Malaria eradicates sickle cell anemia

What happens to the sickle cell allele frequency if malaria is eradicated?

• It becomes more common

• It decreases

• It remains the same

• It increases

What is negative frequency-dependent selection?

• A rare trait has higher fitness only when it is rare

• A rare trait has higher fitness only when it is common

• A common trait has higher fitness only when it is common

• A common trait has higher fitness only when it is rare

In negative frequency-dependent selection, what happens when a rare trait becomes common?

• Its fitness decreases

• Its fitness increases

• Its fitness remains the same

• It becomes extinct

How does negative frequency-dependent selection maintain a trait's rarity?

• By eliminating the trait

• By increasing its fitness when rare

• By decreasing its fitness when rare

• By increasing its fitness when common

What is an example of negative frequency-dependent selection?

• Directional selection

• Heterozygote advantage

• Stabilizing selection

• Predator-prey interactions