USABO - USA Biology Olympiad Evolution and Phylogenetics Questions and Answers

Question 1

A population of 1000 diploid individuals is in Hardy-Weinberg equilibrium.
The population has two alleles, A and a, for a particular gene.
If the frequency of the homozygous recessive genotype (aa) is 0.09, what is the expected number of heterozygous (Aa) individuals in this population?

Accepted Answer

420

Answer

90

Answer

300

Answer

490

Question 2

In a phylogenetic tree, a group of organisms that includes the most recent common ancestor and all of its descendants is referred to as:

Accepted Answer

Monophyletic

Answer

Paraphyletic

Answer

Polyphyletic

Answer

Analogous

Question 3

The evolution of wings in birds and insects is a classic example of convergent evolution. These structures, which serve the same function but have different underlying anatomy and evolutionary origins, are best described as:

Accepted Answer

Analogous structures

Answer

Homologous structures

Answer

Vestigial structures

Answer

Exaptations

Question 4

Which of the following scenarios best illustrates sympatric speciation?

Accepted Answer

The emergence of a new polyploid plant species within the geographic range of its parent species, which can no longer interbreed with the parent population.

Answer

A population of squirrels is separated by the formation of a large canyon, leading to the evolution of two distinct species.

Answer

Two populations of fish in different lakes diverge over time due to unique environmental pressures in each lake.

Answer

A small group of birds colonizes a remote island and, over generations, evolves into a new species distinct from the mainland population.

Question 5

A population of finches on an island primarily eats small, soft seeds. A prolonged drought eliminates the plants that produce these seeds, leaving only plants that produce large, hard-shelled seeds. Over many generations, the average beak depth in the finch population increases. This is an example of:

Accepted Answer

Directional selection

Answer

Stabilizing selection

Answer

Disruptive selection

Answer

Genetic drift

Question 6

The molecular clock hypothesis is a technique used to estimate the divergence time between two lineages. What is the fundamental assumption underlying this hypothesis?

Accepted Answer

The rate of neutral mutations is relatively constant over time among different lineages.

Answer

All mutations are beneficial and become fixed in the population.

Answer

The rate of morphological change is constant over time.

Answer

Fossil evidence is always available to calibrate every node on a phylogenetic tree.

A population of 1000 diploid individuals is in Hardy-Weinberg equilibrium.The population has two alleles, A and a, for a particular gene.If the frequency of the homozygous recessive genotype (aa) is 0.09, what is the expected number of heterozygous (Aa) individuals in this population?

A population of 1000 diploid individuals is in Hardy-Weinberg equilibrium.
The population has two alleles, A and a, for a particular gene.
If the frequency of the homozygous recessive genotype (aa) is 0.09, what is the expected number of heterozygous (Aa) individuals in this population?