GRE Subject Test: Biology : Understanding Phylogenetics

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding 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 B and C eat different things

Populations A and B are both blue

Populations A and C often fight over territory

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

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

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 #2 : Understanding Phylogenetics

Phylogenetics relates organisms to one another based on genetic distance that increases with evolutionary time. This principle requires the use of what kind of genes in order to give accurate relationships?

Possible Answers:

Genes under sexual selection

Genes from the mitochondrial DNA

Genes that are not under selection

Genes under directional selection

Genes from the nuclear DNA

Correct answer:

Genes that are not under selection

Explanation:

In order to derive an accurate estimate of phylogenetic relationships, scientists need to use neutral DNA markers in their studies. If genes are under any sort of selection, it could completely change the results, because this may not reflect the actual evolutionary past of the organisms. It is also generally important to incorporate both nuclear and mitochondrial DNA, because these types of genes can show different histories (remember, mitochondrial DNA is inherited maternally).

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