How do scientists calibrate a molecular clock for a group of organisms with known nucleotide sequences?
A) They use radioactive isotopes to measure the age of DNA material directly.
B) They graph the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record.
C) They analyze fossilized DNA of known age and compare its nucleotide sequences to modern DNA sequences.

Question

Quizplus · Accepted Answer

Scientists use the method of graphing the number of nucleotide differences against known evolutionary branch points from the fossil record to calibrate a molecular clock. By comparing the nucleotide sequences of different organisms, they can estimate how long ago those organisms diverged from a common ancestor. This calibration method assumes a constant rate of DNA mutation over time.

How Do Scientists Calibrate a Molecular Clock for a Group