Which character is shared by the largest number of taxa shown?

Answer: Jaws The character "jaws" is placed at the most basal node after lamprey, so it is shared by sharks, salmon, lizards, and hawks (4 taxa) - more than any other derived character on the tree.

Which pair of taxa shares the most recent common ancestor in this tree?

Answer: A and B A and B share a node deeper in the tree than the node connecting (A,B) with C. So A and B are sister taxa with the most recent common ancestor.

Among the listed taxa, "presence of skull" (marked at the deepest node) is best classified as

Answer: A symplesiomorphy (shared ancestral character) for these taxa A trait inherited from an ancestor and shared across all included taxa is a symplesiomorphy - useful as evidence of common ancestry but not for resolving relationships within the group.

AP Biology · Topic 7.9

Phylogeny Practice

Part of Natural Selection.(EVO-1.I)

Practice questions

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Sample questions

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Sample 1difficulty 1/5
$A cladogram of vertebrate taxa marks the appearance of derived characters at internal nodes.$
$Which character is shared by the largest number of taxa shown?$
- A
  $Bony skeleton$
- B
  $Jaws$
  check_circle
- C
  $Tetrapod limbs$
- D
  $Amniotic egg$
Why
$The character "jaws" is placed at the most basal node after lamprey, so it is shared by sharks, salmon, lizards, and hawks (4 taxa) - more than any other derived character on the tree.$
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Sample 2difficulty 2/5
$Which pair of taxa shares the most recent common ancestor in this tree?$
- A
  $A and B$
  check_circle
- B
  $B and C$
- C
  $All three are equidistant$
- D
  $A and C$
Why
$A and B share a node deeper in the tree than the node connecting (A,B) with C. So A and B are sister taxa with the most recent common ancestor.$
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Sample 3difficulty 2/5
$Among the listed taxa, "presence of skull" (marked at the deepest node) is best classified as$
- A
  $A synapomorphy of birds and lizards only$
- B
  $A symplesiomorphy (shared ancestral character) for these taxa$
  check_circle
- C
  $An autapomorphy of lampreys$
- D
  $A homoplasy$
Why
$A trait inherited from an ancestor and shared across all included taxa is a symplesiomorphy - useful as evidence of common ancestry but not for resolving relationships within the group.$
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Sample 4difficulty 2/5
$A student BLASTs a human cytochrome c protein against five other species. The table shows percent identity of each match.$
$Which inference is best supported?$
- A
  $Humans share a more recent common ancestor with chimpanzees than with yeast.$
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- B
  $Yeast and humans evolved cytochrome c independently.$
- C
  $Tuna are more closely related to chickens than to mice.$
- D
  $Mouse cytochrome c is functionally identical to human cytochrome c.$
Why
$Greater sequence similarity correlates with more recent common ancestry. Chimpanzee at 100 percent indicates the closest relationship; yeast at 63 percent is the most distant.$
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Sample 5difficulty 2/5
$What does the linear relationship between sequence differences and divergence time across taxa support?$
- A
  $Horizontal gene transfer being widespread$
- B
  $A roughly constant molecular clock for the gene$
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- C
  $Selection acting strongly on the gene$
- D
  $Drastic acceleration of mutations in older lineages$
Why
$The molecular clock hypothesis posits that neutral substitutions accumulate at an approximately constant rate over time. A linear plot of differences vs. divergence time supports this clock-like behavior.$
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