GRE Subject Test: Biology : Understanding Phylogenetics
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Example Questions
Example Question #1031 : Biology
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?
Populations A and C often fight over territory
Populations B and C eat different things
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 B are both blue
Populations A and B share similar mtDNA sequences, but differ in their nDNA sequences
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 : Speciation
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?
Genes under directional selection
Genes from the nuclear DNA
Genes that are not under selection
Genes from the mitochondrial DNA
Genes under sexual selection
Genes that are not under selection
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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