Unit 7 · Topic 7.9 end-of-topic test
Suggested time: about 48 minutes. Answer everything, then press Submit the test to see the feedback and scoring guides.
The cladogram shows four trees. The letter J marks one point of the drawing.
What is the marked point?
The cladogram shows five marsupials. An arrow marks one node.
Of which marsupials is the marked node the most recent common ancestor?
The cladogram shows four reptiles.
Which two are the most closely related?
The cladogram shows seven animals.
How many splits does the cladogram record?
The drawing shows four plants; the counts on its scale are imagined.
Which of the following does this drawing show that a cladogram of the same four plants leaves out?
The table gives four characters of four insects. The lacewing is the outgroup.
Which character is an ancestral character for these four insects?
The table gives four characters of four molluscs. The chiton is the outgroup.
Which of these molluscs descend from the ancestor in which the notch or tube for a breathing siphon appeared?
The cladogram shows four primates.
Which primate is the outgroup?
The cladogram shows four fishes, with three characters marked where each arose. Biologists then find a fossil fish.
Which set of characters would place the fossil as the coelacanth’s closest relative on this cladogram?
The cladogram shows four birds; the dove is the outgroup. The letters J to P mark six of its branches. The table gives four characters of the birds.
On which lettered branch did the short, stout, curved bill arise?
Biologists compare one stretch of DNA in four birds and count the positions at which each pair differs, as the table shows. The counts are imagined.
Which two birds join at the node nearest the tips?
Biologists compare one stretch of DNA in five plants and count the positions at which each pair differs, as the table shows; every pair’s count is written twice, and the counts are imagined.
After joining the two most closely related plants, which plant do they add to the tree next?
Biologists compare one stretch of DNA in two kinds of bustard, a large ground bird, and find 30 differences. No fossil dates the split between the two. The count is imagined.
Which one further piece of information would let them estimate how long ago the two lineages split?
Fossils date the split between two kinds of gopher at 6 million years ago. The same stretch of DNA differs between the two at 39 positions. The count and the date are imagined.
What is the rate at which the differences built up?
Biologists compare one stretch of DNA in three kinds of hyrax, a rabbit-sized African mammal. The rock hyrax and the bush hyrax differ at 8 positions, and fossils date their split at 2 million years ago. The rock hyrax and the tree hyrax differ at 22 positions, and no fossil dates their split. The counts and the date are imagined.
How long ago did the rock hyrax’s lineage and the tree hyrax’s split?
Biologists build two cladograms of the same four birds. Cladogram J is built from bill shape and leg length. Cladogram K is built from nine genes. The honeyeater and the sunbird both have long, curved bills for reaching the nectar in flowers, and the two cladograms place them differently.
Which cladogram should biologists accept?
Biologists draw a working cladogram of four trees, as the upper drawing shows. They then compare one stretch of DNA in the four and count the positions at which each pair differs, as the table shows. The counts are imagined.
Which change to the working cladogram does the DNA evidence support?
The phylogenetic tree shows five cats. Its scale gives the time since each split in millions of years, rounded to the nearest million; different studies give somewhat different dates.
Which two cats could be switched while every relationship the tree shows stays the same?
The cladogram shows five plants. An arrow marks one node.
Which two lineages began at the marked node?
(a) Calculate the rate of percent divergence per million years between the hornbill and the hoopoe. Give your answer to two decimal places; the same value to one decimal place is also accepted. (1 point)
Write down the values in the question:
percent divergence, hornbill–hoopoe = 3.6%
time since the split = 4 million years
Write down the equation:
Substitute the values into the equation:
A full-credit answer: The hornbill and the hoopoe differ at 3.6% of positions, and fossils date their split at 4 million years ago.
3.6 ÷ 4 = 0.90% per million years.
(b) Determine which bird belongs at each of the blank tips J, K, L and M of the template. (1 point)
A full-credit answer: J and K: the hornbill and the hoopoe, in either order. Their divergence, 3.6%, is the smallest in the table, so they join at the node nearest the tips.
L: the roller, at 6.8% and 7.0% from the pair, the next smallest.
M: the trogon, at 10.2% to 10.5% from those three.
Check the box for each point your answer earns
(c) Justify the placement of the turaco as the outgroup. (1 point)
A full-credit answer: The turaco’s divergence from every other bird is the largest in the table: 15.1% to 15.6%.
The bird most different from all the others is the least closely related to them.
So its lineage is the first off the root: the outgroup.
Check the box for each point your answer earns
(d) Identify every bird that descends from the node marked with the arrow. (1 point)
A full-credit answer: The arrowed node is the one where L’s line joins the J–K pair.
Three tips rise from it: J, K and L.
So the hornbill, the hoopoe and the roller descend from it.
Check the box for each point your answer earns
(a) Describe how a scientist would use a comparison of DNA sequences from different plants to suggest the most likely evolutionary relationships among them. (1 point)
A full-credit answer: The scientist compares the same stretch of DNA in each plant and counts the positions at which each pair differs.
Fewer differences mean a more recent common ancestor.
So the pair with the fewest differences is placed as the closest relatives, and the plant most different from all the others as the outgroup.
Check the box for each point your answer earns
(b) Based on Figures A and B, explain why the spurge is likely to be more closely related to the peony than to the aloe. (1 point)
A full-credit answer: In Figure B the spurge’s and the peony’s lines join at a node just below them; the aloe’s line joins the spurge’s only at the root.
Figure B is built from DNA: thousands of independent characters that a shared way of life almost never makes alike.
So the DNA cladogram is the more reliable one, and it places the spurge with the peony.
Check the box for each point your answer earns
(c) Using Figure B, identify the lettered branch or branches on which thick, water-storing leaves or stems arose. (1 point)
A full-credit answer: The aloe and the agave both have the character, so it arose once on the branch below their shared node: L.
The spurge has it, but the peony beside it does not, so it arose again on the spurge’s own branch: M.
So the character arose on branches L and M.
Check the box for each point your answer earns
(d) Based on Figure A, explain why a feature found only in the agave and the peony would more likely have arisen separately in the two lineages (convergent evolution) than have been inherited from one common ancestor. (1 point)
A full-credit answer: On Figure A the only ancestor the agave and the peony share is the root.
The aloe, the spurge and the jasmine descend from the root too, and they lack the feature.
One origin at the root would need three later losses: four events.
Two separate origins are two events, the simpler explanation.
Check the box for each point your answer earns
Accept one of the following: other plants that descend from the same common ancestor (the aloe, the spurge, the jasmine) lack the feature; or two separate origins are fewer events than one origin in the common ancestor followed by losses in the aloe, the spurge and the jasmine.