Final answer:
The accurate statement is that the net fitness effect of an allele experiencing antagonistic pleiotropy may depend on the environment. Selection of alleles depends on specific environmental conditions, which can change the fitness associated with those alleles, influencing their frequency within the population.
Step-by-step explanation:
Antagonistic pleiotropy occurs when one gene influences multiple traits in a way that is beneficial in some aspects but detrimental in others. The accurate statement about antagonistic pleiotropy is that the net fitness effect of an allele experiencing antagonistic pleiotropy may depend on the environment. This is observable in cases like the sickle-cell trait (S allele), which provides a protective effect against malaria but causes sickle-cell disease in homozygous conditions. When environmental factors change, such as the elimination of malaria, the fitness benefits of having the S allele would likely decrease, consequently affecting its frequency in the population. This scenario demonstrates that alleles experiencing antagonistic pleiotropy are not always strongly selected against; instead, their selection depends on specific environmental contexts.
For example, an allele might confer a survival advantage under one set of conditions, like resistance to malaria, but might be disadvantageous under different conditions if the disease were not present. In the absence of malaria, individuals with the S allele might be less fit due to the risk of developing sickle-cell anemia, impacting the allele's frequency over time through natural selection. Similarly, Moree's experiments with Drosophila melanogaster showed that environmental factors like population density could alter the relative fitness of an allele causing black eye color in flies.
Furthermore, traits influenced by pleiotropy illustrate why some deleterious mutations are maintained in the population. Alleles that might seem disadvantageous in one context can persist because of their advantages in another, as with the multiple effects of a single gene.