Many Plant Species Are Hermaphroditic and Run the Risk of Self-Mating

Multiple Choice

Many plant species are hermaphroditic and run the risk of self-mating. Some species carry self-incompatibility alleles that can prevent this from occurring. If a pollen grain with self-incompatibility allele S₁ lands on a stigma that also carries the S₁ allele, the pollen will not germinate and fertilization does not occur. Thus, this mechanism not only prevents selfing, but also has the unfortunate effect of preventing mating with any other plant that carries the same allele. However, if the pollen lands on a stigma of a plant with a different allele, fertilization occurs. Imagine a population of plants in which the allele frequency of S₁ = 0.9 and the allele frequency of S₂ = 0.1. All other things being equal, individuals with the ____ allele will have higher fitness on average. This is an example of ______.

A) S₁; positive selection
B) S₂; positive selection
C) S₁; negative frequency-dependent selection
D) S_2; negative frequency-dependent selection