Question

1 multiple choice 16.6 points
dok 3: how does a sudden, severe environmental change, such as a volcanic eruption, most directly affect the evolutionary trajectory of a small, isolated population of organisms?
by eliminating all competition, allowing every individual to survive and reproduce and pass on their genes.
by immediately increasing the populations overall fitness level, drastically increasing the survival rate.
by introducing new, beneficial alleles through increased gene flow in the populations, due to the fact that new organisms will move into the area.
by accelerating natural selection and potentially causing a rapid bottleneck effect, severely limiting genetic variation.
2 multiple choice 16.6 points
dok 1: natural selection acts directly on which of the following?
allele frequencies.
mutations.
genotypes (allele combinations).
phenotypes (physical traits).

Explanation:

1. A volcanic eruption is a severe environmental change. In a small, isolated population, it can lead to a bottleneck effect (a sharp reduction in population size). This accelerates natural selection as only those individuals that can survive the harsh conditions (like the aftermath of a volcanic eruption) will pass on their genes. The first option is wrong because a volcanic eruption would not eliminate all competition and allow every individual to survive (the harsh conditions would kill many). The second option is incorrect as a volcanic eruption would likely decrease fitness (due to destruction of habitat, etc.). The third option is wrong because in an isolated population, there is no gene flow (new organisms moving in) as it is isolated.
2. Natural selection acts on phenotypes. Phenotypes are the physical expressions of genes (like the color of a flower, the height of an animal). Natural selection “sees” how well an organism’s phenotype helps it survive and reproduce in its environment. Allele frequencies are affected by natural selection (as certain alleles that code for favorable phenotypes become more common), but natural selection acts directly on phenotypes. Mutations are random changes in DNA and natural selection acts on the phenotype that may result from a mutation. Genotypes (allele combinations) determine phenotypes, but again, natural selection acts on the observable phenotype.

Answer:

1. By accelerating natural selection and potentially causing a rapid bottleneck effect, severely limiting genetic variation.
2. Phenotypes (physical traits).