Question

Name the phenomenon being described in each of these (hypothetical) examples, and describe how it is likely to affect allele frequencies in succeeding generations.

a. A beetle species is introduced to an island cov- ered with dark basaltic rock. On this dark back- ground, dark beetles, TT or Tt, are much more resistant to predation than are light-colored bee- tles, tt. The dark beetles have a large selective advantage. Both alleles are relatively common in the group of beetles released on the new island.
b. Another beetle population, this time consisting of mostly light beetles and just a few dark beetles, is introduced onto a different island with a mixed substrate of light sand, vegetation, and black ba- salt. On this island, dark beetles have only a small selective advantage.
c. A coral-reef fish has two genetically determined types of male. One kind of male is much small- er than the other, and sneaks into larger males' nests to fertilize their females' eggs. When small males are rare, they have a selective advantage over large males. However, if there are too many small males, large males switch to a more aggres- sive strategy of nest defense, and small males lose their advantage.
d. In a tropical plant, CC and Cc plants have red flowers and cc plants have yellow flowers. How- ever, Cc plants have defective flower develop- ment and produce very few flowers.
e. In a species of bird, individuals with genotype MM are susceptible to avian malaria, Mm birds are resistant to avian malaria, and mm birds are resistant to avian malaria, but the mm birds are also vulnerable to avian pox.

Answer 1

The phenomenon being described in these examples is natural selection and sexual selection. These phenomena can affect allele frequencies in succeeding generations by favoring individuals with certain alleles or genotypes.

Step-by-step explanation:

The phenomenon being described in example a is natural selection. The introduction of dark beetles to an island covered with dark basaltic rock gives them a selective advantage over the light-colored beetles. As a result, the frequency of the dark alleles (TT or Tt) will likely increase in succeeding generations.

Example b also describes natural selection. In this case, the dark beetles have a small selective advantage due to the mixed substrate of light sand, vegetation, and black basalt on the island. The frequency of the dark alleles may increase over time.

Example c involves sexual selection. When small males are rare, they have a selective advantage over large males. However, if there are too many small males, large males switch to a more aggressive strategy of nest defense, and the small males lose their advantage. This phenomenon can affect allele frequencies by altering the reproductive success of males with different genotypes.

Example d is an example of incomplete dominance. The CC and Cc plants have red flowers, while the cc plants have yellow flowers. However, the Cc plants have defective flower development and produce very few flowers. This defect can affect allele frequencies by reducing the reproductive success of individuals with the Cc genotype.

Example e involves multiple allelic interactions. The MM birds are susceptible to avian malaria, Mm birds are resistant to avian malaria, and mm birds are resistant to avian malaria but vulnerable to avian pox. This phenotypic variation can affect allele frequencies depending on the selective pressure of the diseases and the relative fitness of the different genotypes.