Name ______________________________ Class ___________________ Date __________________
Section 3: Molecular Clocks
Study Guide B
KEY CONCEPT
Molecular clocks provide clues to evolutionary history.
VOCABULARY
molecular clock
mitochondrial DNA
ribosomal RNA
MAIN IDEA: Molecular clocks use mutations to estimate evolutionary time.
1. What are molecular clocks?
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2. Explain how species become more and more different at the molecular level,
after they have diverged from a common ancestor.
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3. Using Figure 3.1 as a reference, draw your own set of DNA sequences that
illustrate molecular evolution.
4. How can scientists estimate mutation rates for use in developing a molecular
clock?
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© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
1
The Tree of Life
Section 3: Molecular Clocks
Name ______________________________ Class ___________________ Date __________________
Study Guide B continued
MAIN IDEA: Mitochondrial DNA and ribosomal RNA provide two types of
molecular clocks.
5. Depending on how closely related species are, scientists must choose a
molecule with an appropriate _____________ rate to use as a molecular clock.
6. In the table below, take notes about two commonly used molecular clocks.
Molecular Clock
Description of
Molecule
Why It’s Unique
How It’s Useful as
a Molecular Clock
mtDNA
tRNA
Vocabulary Check
molecular clock
mitochondrial DNA
ribosomal RNA
_______________ 7. Useful for studying closely related species
_______________ 8. Model that uses mutation rates to measure evolutionary time
_______________ 9. Useful for studying species in different kingdoms or phyla
© Houghton Mifflin Harcourt Publishing Company
Holt McDougal Biology
Study Guide B
2
The Tree of Life
Section 3: Molecular Clocks