Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
    
Click to return to the Evolution Home Page
darwin change extinction survival sex humans religion
Online Course for Teachers: Teaching Evolution

About this Course 

SESSION 3

SESSION 3: What Is the Evidence for Evolution?

Elaborate Part B: Molecular Clocks

Molecular biologists are able to determine and compare the DNA base sequences and the amino acid sequences of the same proteins from different animals. The less closely related species are, the more differences there are in their DNA base or amino acid sequences, because there is more time for mutations to accumulate. Conversely, the more closely related species are, the fewer differences there are.

Read these documents: "Relationships of Living Species: Calibrating Molecular Clocks" (pdf) and "Molecular Clocks: Proteins That Evolve at Different Rates" (pdf).

Summarize the answers to these questions:

• 

What are molecular clocks, and how do they help determine relationships between species?

• 

How do the rates of mutation vary for different proteins?

• 

How reliable are molecular clocks?

 



 

Next: Evaluate Part A: All in the Family

 
Videos Web Activities Site Guide About the Project FAQ Glossary Site Map Feedback Help Shop