MCAT Biology : Speciation and Phylogenetics

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Speciation And Phylogenetics

A scientist studies three populations of frog (populations A, B, and C) that live in the same rainforest. He notices some interesting similarities between the three groups. What would be the best evidence that A and B have a more recent common ancestor than A and C or B and C?

Possible Answers:

Populations A and B are not native to the rainforest, but came from two different areas that were very similar to the rainforest

Populations A and B share similar mtDNA sequences, but differ in their nDNA sequences

Populations A and C often fight over territory

Populations A and B are both blue

Populations B and C eat different things

Correct answer:

Populations A and B share similar mtDNA sequences, but differ in their nDNA sequences

Explanation:

Mitochondrial DNA (mtDNA) is only inherited directly from a mother to her offspring and can be used to directly track lineage of a population or species. Nuclear DNA (nDNA) is inherited from both the father and mother of the offspring; it can be used to track lineage as well, but mtDNA similarity is enough to conclude a close relationship between the two populations described in the question.

Color, diet, and location are all distinguishing features of the populations and help characterize their niche in the ecosystem. Diet and location (territory) are not heritable traits, and do not signify ancestry. Color is genetic, but could result from convergent or divergent evolution. mtDNA similarity is the strongest available evidence for a close ancestral link between populations A and B.

Example Question #1033 : Biology

A certain class of protein is found to exist in several different species. The amino acid sequence of this protein is compared between a large number of species. The greatest number of amino acid differences will be found between species of different __________.

Possible Answers:

genera

phyla

families

orders

Correct answer:

phyla

Explanation:

The higher the taxonomic group, the less similar the members are. This is true for appearance, behavior, and genetics. The order of taxonomic groupings, from most general to most specific is: kingdom, phylum, class, order, family, genus, species.

Of the given answers, phyla are the highest taxonomic rank. Species of different phyla would show the greatest genetic difference. In contrast, genera are the lowest taxonomic rank of the given answers; species of the same genus would show the least genetic difference.

Example Question #2 : Speciation And Phylogenetics

Which of the following is not necessary for designation as a chordate?

I.  A notochord

II.  Vertebrae

III.  A post-anal tail

IV.  Gill arches 

V.  A dorsal, tubular nervous system

Possible Answers:

V

I

IV

III

II

Correct answer:

II

Explanation:

Chordates must have, at some point in their embryogenesis, all features except vertebrae. Although the vast majority of chordates are vertebrates, Amphioxus has only a notochord. This primitive organism never develops vertebrae. Man has gill arches, and remnants of these are seen in certain congenital malformations. The notochordal remnants can give rise to the tumor known as a chordoma. The brain has ventricles (it is tubular) and it is certainly dorsal. Finally, human tail persists in about one per million live births.  

Example Question #3 : Speciation And Phylogenetics

Which of the following statements about chordates is true?

Possible Answers:

Their anus forms from the blastopore

All chordates are vertebrates

They are protostomes

They lack a coelom 

Correct answer:

Their anus forms from the blastopore

Explanation:

The phylum chordata has a few key characteristics. They are deuterostomes, meaning that the anus arises from the blastopore. They have a coelom that arises from the mesoderm during development, and at some point they have a tail, pharyngeal slits, and a notochord.

Vertebrata is a subphylum of chordata, so not all chordates are vertebrates (though all vertebrates are chordates).

Example Question #1 : Understanding Types Of Animals

Which of the following is false of the phylum chordata?

Possible Answers:

They have a coelom

They have a notochord at some point in their development

They have bilateral symmetry

They are protostomes

Correct answer:

They are protostomes

Explanation:

All chordates are deuterostomes, not protostomes. During early development, the formation of the blastopore leads to the growth of the digestive tract. In protostomes, the blastopore develops into the mouth, while in deuterostomes it becomes the anus.

All chordates have a notochord during development, which eventually gives rise to the nervous system. Chordates also have a coelom, or fluid filled cavity, somewhere within the body and they all exhibit bilateral symmetry.

Example Question #4 : Speciation And Phylogenetics

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. 

A white-feathered flamingo mates with a pink-feathered flamingo, and produces a pink-feathered flamingo offspring. Two students debate as to whether or not this offspring is the same species as its parents, since its feather color differs from that of one of its parents. Which of the following examples best represents the evolutionary definition of a species?

Possible Answers:

One animal mates with another animal and produces viable offspring that are capable of reproducing successfully.

One animal lives in a closed environment with 250 to 500 other animals that look similar to one another and  support each others' basic needs (food, shelter, protection). 

One animal mates with another animal and produces viable offspring that are not capable of reproducing successfully.

One animal lives in a closed environment with greater than 500 other animals that look similar to one another and support each others' basic needs (food, shelter, protection).

Correct answer:

One animal mates with another animal and produces viable offspring that are capable of reproducing successfully.

Explanation:

The only absolutely correct answer is the one that states that an animal can successfully mate with another animal and produce viable offspring that are capable of successfully reproducing. The key to defining a species is that the offspring are both viable and fertile. The correct answer encompasses both of those tenets.

"One animal mates with another animal and produces viable offspring that are not capable of reproducing successfully." This choice is incorrect because it states that the offspring are not fertile.

"One animal lives in a closed environment with 250 to 500 other animals that look similar to one another and support each others' basic needs (food, shelter, protection)." This example may describe a species, but there is not enough information to definitively conclude that. It does not explicitly state that the animals successfully mate with one another, or that their offspring (if they do mate with each other) are fertile. 

"One animal lives in a closed environment with greater than 500 other animals that look similar to one another and support each others' basic needs (food, shelter, protection)." This example may describe a species, but there is not enough information to definitively conclude that. It does not explicitly state that the animals successfully mate with one another, or that their offspring (if they do mate with each other) are fertile.

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