Question

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 event 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. Individuals with the S1 allele will have higher fitness; disruptive selection
b. Individuals with the S2 allele will have higher fitness; stabilizing selection
c. Individuals with the S1 allele will have higher fitness; directional selection
d. Individuals with the S2 allele will have higher fitness; balancing selection

Answer 1

Individuals with the S2 allele will have higher fitness due to increased opportunities for cross-pollination in a population where S2 is less common; this scenario demonstrates balancing selection.

Step-by-step explanation:

In a population of plants where the allele frequency of S1 is 0.9 and the frequency of S2 is 0.1, individuals with the S2 allele will have higher fitness on average.

This is because plants with the S2 allele are less likely to encounter another S2 plant, and therefore have a higher chance of successful cross-pollination, leading to increased fitness. This situation is an example of balancing selection, where genetic diversity is maintained within a population.