Question at position 2 Below are two figures: a dated phylogeny of primates (top) a graph showing the relationship between the number of base pair substitutions (differences) in the cytochrome c gene between two taxa since the time they shared a common ancestor (bottom). Given this information, what is the most likely number* of base pair substitutions between the Aye-aye and Indri? *answers represent a range of base pair substitutions 45-5025-3075-8035-4058-63Clear my selection单项选择题
A
45-50
B
25-30
C
75-80
D
35-40
E
58-63

Question

Question at position 2 Below are two figures: a dated phylogeny of primates (top) a graph showing the relationship between the number of base pair substitutions (differences) in the cytochrome c gene between two taxa since the time they shared a common ancestor (bottom). Given this information, what is the most likely number* of base pair substitutions between the Aye-aye and Indri? *answers represent a range of base pair substitutions 45-5025-3075-8035-4058-63Clear my selection单项选择题

A

45-50

B

25-30

C

75-80

D

35-40

E

58-63

BlackTom AI · Accepted Answer

To tackle this question, I’ll walk through each answer option by linking the two figures: the dated primate phylogeny and the molecular clock of cytochrome c. The key idea is that the molecular clock shows substitutions accumulating roughly linearly with time since the last common ancestor, so you match the approximate time since divergence to the corresponding number of substitutions.

Option 45-50: This range suggests a modest number of substitutions. Looking at the molecular clock panel, the line is approximately linear with time, and around the mid-point of the x-axis (roughly 60 million years since the last common ancestor), the corresponding y-value is near 60 substitutions. A value of 45-50 would place the divergence earlier than 60 Myr, which contradicts the depicted proportionality. Therefore this range underestimates substitutions for the Aye-aye and Indri pair.

Option 25-30: This is even lower, implying a very early divergence. The graph’s slope indicates substantially more substitutions by the time you reach 60 Myr, so 25-30 would be inconsistent with the shown rate and would imply an unrealistically slow clock relative to the time scale presented. This option is likely incorrect.

Option 75-80: This range would correspond to a later divergence than 60 Myr, or to a faster rate than depicted. Since the molecular clock line appears to pass through approximately 60 substitutions at around 60 Myr, 75-80 substitutions would place the split well after 60 Myr or require a steeper-than-illustrated slope. Thus this overestimates substitutions for the Aye-aye and Indri pair given the shown data.

Option 35-40: Similar to 45-50, this range underestimates the number of substitutions for the given time point. At roughly 60 Myr, the line on the clock is closer to 60 substitutions, so 35-40 does not align with the graph’s trend.

Option 58-63: This narrow range sits closest to the point where the line on the molecular clock intersects near 60 substitutions at about 60 Myr. It aligns with the linear relationship shown: time since last common ancestor roughly corresponds to an equal magnitude of substitutions. This option best matches the depicted data.

In summary, each of the first four ranges underestimates or overestimates substitutions when tied to the illustrated time scale, while 58-63 best reflects the proportional rise of substitutions with time on the molecular clock plot for the Aye-aye and Indri lineages.

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