Correct option is D
Frequency-dependent selection refers to a situation where the fitness of a genotype depends on how common or rare it is within the population. Typically, negative frequency-dependent selection maintains genetic polymorphisms by favoring rare genotypes. However, if frequency-dependent selection favors the common morph (positive frequency-dependent selection), it can reduce polymorphism by causing the more common morph to be more successful and dominate the population. Therefore, positive frequency-dependent selection can not maintain genetic polymorphisms.
Information Booster:
- Polymorphism Maintenance: Natural selection can maintain genetic polymorphisms in a population through various mechanisms that preserve genetic diversity.
- Environmental Heterogeneity: If the direction of selective forces is different in different environments, it can help maintain polymorphisms, as different traits will be favored in different environments.
- Heterozygote Advantage: When heterozygotes have superior fitness compared to homozygotes (e.g., in the case of sickle cell anemia and malaria resistance), this can maintain both alleles in the population.
- Selective Gradients: Gradients of selective forces favoring different morphs can also help maintain polymorphisms by favoring different traits in different environmental conditions.
- Negative Frequency-Dependent Selection: In contrast to positive frequency-dependent selection, negative frequency-dependent selection helps maintain polymorphisms by favoring rarer traits.
Additional Information:
Option (a) - When the direction of selective forces is different in different environments: This contributes to polymorphism maintenance because different traits will be advantageous in different environments, promoting genetic diversity.
Option (b) - When heterozygotes have superior fitness over homozygotes: This is a well-known mechanism that maintains polymorphisms, such as the case with sickle cell anemia, where heterozygotes have a fitness advantage over homozygotes.
Option (c) - When gradients of selective forces favor different morphs: This can maintain polymorphisms because different morphs (traits) may be favored depending on environmental gradients, such as altitude, habitat, or diet.
