How Do Scientists Calibrate a Molecular Clock for a Group

question 20

Multiple Choice

How do scientists calibrate a molecular clock for a group of organisms with known nucleotide sequences?

• A)They measure protein differences. Evolutionary rates in proteins are well-known and can be used to check results obtained using nucleotide sequences.
• B)They use radioactive isotopes to measure the age of DNA material directly.
• C)They graph the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record.
• D)They analyze fossilized DNA of known age and compare its nucleotide sequences to modern DNA sequences.

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