MCAT Biology : Types of Evolution and Speciation

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Types Of Evolution And Speciation

Seven thousand years ago, a species of oryx indigenous to the Arabian Peninsula was separated when an earthquake caused an insurmountable barrier to form between different geological segments of the population. A recent population genetics study showed that the two populations were no longer able to successfully interbreed.

Careful testing of these two species found that a physiological change in one species was responsible for the mating incompatibility between the two populations. Which of the following answer choices best describes the nature of this mating incompatibility?

Possible Answers:

Mechanical difference

Temporal difference

Inherent difference

Genetic difference

Correct answer:

Mechanical difference

Explanation:

A physiological condition making two speciated animals unable to mate is a mechanical difference.

Example Question #2 : Types Of Evolution And Speciation

A population of saltwater fish has doubled in body length and decreased in body width over the past decade. This has been attributed to overfishing using nets with large holes. This type of selection is most accurately __________.

Possible Answers:

disruptional selection

phenotypical selection

stabilizing selection

unnatural selection

directional selection

Correct answer:

directional selection

Explanation:

Directional selection is when a population undergoes a change biased in a certain direction away from the original average of the population. Since the fish are getting bigger in once sense and smaller in another, this is directional selection.

Example Question #3 : Types Of Evolution And Speciation

Seven thousand years ago, a species of oryx indigenous to the Arabian Peninsula was separated when an earthquake caused an insurmountable barrier to form between different geological segments of the population. A recent population genetics study showed that the two populations were no longer able to successfully interbreed.

What type of speciation event does this information indicate? 

Possible Answers:

None of these

Peripatric speciation

Allopatric speciation

Artificial speciation 

Parapatric speciation 

Correct answer:

Allopatric speciation

Explanation:

Allopatric speciation occurs when a physical barrier, or in some cases emigration of subpopulations of a species, prevents interspecies mingling that eventually leads to the inability to interbreed. Sympatric speciation describes a process by which new species form while in the same geographic location. Parapatric and peripatric speciation are subcategories of sympatric speciation.

Example Question #4 : Types Of Evolution And Speciation

Passage:

A population of 1200 flamingos exists on an island in the tropics. The flamingos had previously been studied for many years due to their fascinating foraging habits. Many flamingos within this population hunt their prey out in the open, without any attempts to disguise themselves, which some feel predisposes them to being seen by their prey and evaded, or even attacked, sooner than flamingos who more stealthily hunt their prey. Still, so many of these flamingos continue to live viably and reproduce highly successfully, so it has puzzled scientists for years that this is an "evolutionarily successful" strategy. Of the 1200 flamingos initially present, 800 had pink feathers and 400 had white feathers. A tragic hurricane then struck the island, killing all but 10 of the flamingos. 8 of these 10 had white feathers. Years later, scientists again studied the flamings on the island and found a population of 600 flamingos. Of the 600 flamingos, 560 had white feathers and 40 had pink feathers. 

Which of the following evolutionary principles best describes the situation present in the passage above?

Possible Answers:

Selective Mating

Genetic Drift

Bottlenecking

Genetic Engineering

Spontaneous Mutation

Correct answer:

Bottlenecking

Explanation:

The situation described is a classic example of the evolutionary principle of "bottlenecking," making this the best answer choice. Bottlenecking describes the phenomenon in which the genetic diversity of a population changes suddenly, often due to a natural disaster, which then results in future generations appearing more genetically and phenotypically similar to one another than in the pre-disaster generations. In this instance, pink flmaginos were initially more common than white flamingos, but both were fairly prevalent. They then encounter a hurricane that kills all but a few flamingos, which were almost entirely white-feathered, which led to all ensuing generations being predominantly white-feathered. 

This does not represent "selective mating," "spontaneous mutation," or "genetic engineering," as white-feathered flamingos became most prevalent due to a natural disaster, not white flamingos selectively seeking to mate with other white flamingos, not due to a single mutation, and not due to scientists artificially manipulating the genes within the flamingos. 

This does not represent "genetic drift," because the changes in phentype prevalence were not due to random chance fluctuations, they were due to an explainable event, a natural disaster that resulted in an initially low number of white flamingos remaining and becoming most predominant.

 

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