Molecular Evidence
What two types of molecules can scientists compare to determine evolutionary relationships?
DNA and proteins/amino-acid sequences.
What does a node, or branch point, represent on a cladogram?
A common ancestor.
A phylogenetic tree represents a hypothesis about what?
Evolutionary relationships/history among organisms.
What do we call preserved remains or evidence of organisms from the past?
Fossils
What term means the formation of a new species?
Speciation
Two organisms have very similar amino-acid sequences for the same protein. What does this suggest?
They likely share a relatively recent common ancestor.
┌── A
──────●───┤
└── B
Question: What can you conclude about Species A and B?
They share a common ancestor.
Question: TRUE or FALSE:
Two organisms that are physically next to each other on a phylogenetic tree are always the most closely related.
FALSE
What type of fossil contains characteristics that help scientists understand evolutionary changes between ancestral and descendant groups?
Transitional Fossil
Similarities in the embryonic development of different species provide what type of evidence?
Developmental evidence/homology
Question: Which species is MOST closely related to the Mystery species?
Species A
┌── A
┌────┤
│ └── B
───────────────┤
└──────── C
Which species is MOST closely related to Species A?
Species B
Why: A and B share the most recent common ancestor.
┌── Lion
┌────┤
│ └── Tiger
┌────┤
│ └────── House Cat
───────────────┤
└─────────── Wolf
Is the lion more closely related to the tiger or the house cat?
Tiger
Scientists discover many transitional fossils in successive rock layers.
Question: What pattern of evolutionary change does this evidence support?
Gradualism
A dolphin embryo temporarily begins developing hind limbs, but they disappear before birth.
Question: What does this BEST suggest about dolphin ancestry?
Dolphins descended from ancestors that possessed hind limbs.
Question: Rank B, C, and D from most closely related to least closely related to Species A.
Answer: B → C → D
Why: Fewer amino-acid differences indicate greater molecular similarity.
┌── A
┌────┤
│ └── B
┌────┤
│ └────── C
───────────────┤
└─────────── D
Which species is least closely related to Species A?
Species D
┌── A
┌────┤
│ └── B
┌────┤
│ └────── C
───────────────┤
└─────────── D
Explain WHY Species A is more closely related to B than C.
A and B share a more recent common ancestor than A and C.
Scientists discover a 150-million-year-old fossil plant. Its physical characteristics are extremely similar to members of the same lineage living today.
Question: What evolutionary pattern does this evidence BEST demonstrate?
Stasis
A fossil lineage shows:
small change → small change → small change → small change → small change
over millions of years.
Question: Which model BEST describes this pattern?
Gradualism
Question: Which organism most likely shares the most recent common ancestor with Species X, and what evidence supports your answer?
Species B, because it has the greatest protein similarity (96%) to Species X.
Fish Frog Lizard Cat
│ │ │ │
─┴───────────┴─────────────┴───────────┴──
↑ ↑ ↑ ↑
Backbone 4 limbs Amniotic egg Hair
Which organisms possess the derived characteristic four limbs, and how can you tell?
Frog, lizard, and cat. They branch after the four-limbs characteristic appears.
┌── Species A
┌────┤
│ └── Species B
┌────┤
│ └────── Species C
┌────┤
│ └─────────── Species D
──────────┤
└──────────────── Species E
Question: Which two species share the least recent common ancestor?
A. Species A and Species B
B. Species A and Species C
C. Species B and Species D
D. Species A and Species E
D. Species A and Species E
Explanation: To find the least closely related pair, trace the branches backward. A and E do not share a common ancestor until the oldest/deepest node shown on the tree.
A new group appears relatively suddenly in the fossil record with few transitional fossils immediately preceding it.
Question: What is this pattern called?
Abrupt appearance
Two environments are compared:
Environment A: Remains relatively stable for millions of years.
Environment B: Experiences a rapid, large-scale environmental disturbance.
Question: Which environment would be MORE likely to be associated with a period of relatively rapid evolutionary change?
Environment B