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.

Question

Quizplus · Accepted Answer

Scientists use the molecular clock method to estimate the time of divergence between two species based on the amount of genetic difference between them. To calibrate the molecular clock, scientists plot the number of nucleotide differences against the dates of evolutionary branch points that are known from the fossil record. This allows them to estimate the rate of molecular evolution for that specific group of organisms. Choice A is incorrect because measuring protein differences is not a direct method for calibrating molecular clocks. Choice B is incorrect because radioactive isotopes are not used to date DNA material directly. Choice D is incorrect because fossilized DNA is rare and the chances of finding it for a particular group of organisms is unlikely.

How Do Scientists Calibrate a Molecular Clock for a Group