High School

A person flies from one continent to another. Unknowingly, he boards the plane with a few seeds attached to the laces of his hiking boots. As he is hiking at his destination, these seeds drop off and become planted. The seeds grow and interbreed with a closely-related native species also found at that location. After a few generations, the population where the seeds dropped has flowers with different shapes compared to the surrounding populations in the forest.

This is an example of

A. gene flow
B. genetic drift
C. selection
D. disruptive selection

Which of the following mechanisms will MOST consistently result in populations that adapt to a changing environment?

A. gene flow
B. genetic drift
C. selection
D. natural selection

Which of the following could result in allopatric speciation?

A. Two populations of a species are separated by a river that they are unable to cross.
B. Two populations of a species are separated by a field that is too dry during the summertime.
C. One group within a population mates during the evenings and another during the mornings.
D. One group within a population develops a new mating ritual that is not recognized by the other.

Which process in a hybrid zone increases the likelihood of speciation?

A. stability – when a hybrid zone remains the same
B. reinforcement – when a hybrid zone widens and fewer hybrids are formed
C. convergence – when a hybrid zone narrows and more hybrids are formed
D. fusion – when a hybrid zone disappears and separate species fuse into one

Based on current knowledge, which cellular trait is MOST likely the oldest?

A. photosynthesis
B. multicellularity
C. presence of a nucleus
D. presence of chloroplasts

Adaptive radiation is when

A. a species develops a new trait.
B. several species move to a new location.
C. the number of species in an area rapidly increases in number.
D. the number of species in an area rapidly decreases in number.

Hox genes regulate the development of

A. the body plan of an embryo.
B. gametes.
C. the respiratory system only.
D. the circulatory system only.

Evolution results in an increase of organisms that are

A. larger.
B. more complex.
C. better suited to the current environment.
D. better able to adapt to changing environments.

Where on a phylogeny are ancestral organisms for two groups found?

A. at the end of the rightmost branch
B. at the end of the leftmost branch
C. on the nodes between the two groups
D. as a perpendicular line crossing a branch

Answer :

The person unknowingly carrying seeds is an example of gene flow (option A). The most consistent mechanism for adaptation to a changing environment is selection (option D), specifically natural selection. Allopatric speciation often occurs due to geographic barriers, and reinforcement (option B) in hybrid zones increases the likelihood of speciation. The presence of a nucleus (option C) is likely the oldest cellular trait, while Hox genes regulate embryonic body plans (option A).

  • The situation described where a person unintentionally transferred seeds from one continent to another that eventually interbred with a native species is an example of gene flow (option A). After a few generations, the resulting population has flowers with different shapes, reflecting the exchange of genetic material between populations.
  • The mechanism that most consistently results in populations adapting to a changing environment is selection (option D), especially natural selection. This process consistently favors individuals that are better suited for their environment, leading to an increase in the frequency of advantageous traits over time.
  • Allopatric speciation could result when two populations of a species are separated by a river that they cannot cross (option A). The geographic separation prevents gene flow between the populations, allowing them to evolve independently.
  • In a hybrid zone, the process that increases the likelihood of speciation is reinforcement (option B). This occurs when hybrids are less fit than the parent species, leading to a reduction in hybrid formation and strengthening the distinction between species.
  • The cellular trait that is most likely the oldest is the presence of a nucleus (option C), a key feature of eukaryotic cells.
  • Adaptive radiation refers to a scenario where the number of species in an area rapidly increases in number (option C), often following colonization of a new area or an extinction event that opens up new ecological niches.
  • Hox genes regulate the development of the body plan of an embryo (option A), influencing the arrangement and the segmented structure of tissues and organs.
  • Evolution tends to result in an increase of organisms that are better suited to the current environment (option C), as natural selection favors those traits that enhance survival and reproduction under prevailing conditions.
  • On a phylogeny, ancestral organisms for two groups are found at the nodes between the two groups (option C), representing the common ancestor from which the two groups diverged.