SAT Subject Biology Practice Question 167: Answer and Explanation

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Question: 167

17. Scientists constructed a phylogenetic tree of modern lizard genera based on DNA sequences, shown below.

Within this group of lizards, several genera have evolved characteristics similar to those found in snakes. One mutation contributed to a diminished external ear in the genera indicated by an asterisk. What is the most recent point at which this mutation most likely occurred?

A. After Aprasiadiverged from Paradelma
B. After Lialisdiverged from Pletholax
C. When Aprasiaand Pletholaxlast shared a common ancestor
D. When Lialisand Pygopuslast shared a common ancestor
E. After Aprasiadiverged from Ophidiocephalus

Correct Answer: A


The diminished-ear phenotype is present in the genera Aprasia, Ophidiocephalus, and Pletholax. The mutation leading to this phenotype must therefore have occurred before these branches diverged from a common ancestor but after they diverged from other groups.

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