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

Question

Quizplus · Accepted Answer

Scientists calibrate a molecular clock for a group of organisms with known nucleotide sequences by graphing the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record. This allows them to estimate the rate of evolution for that group and use it to estimate the time of divergence for other species within that group. Option A is not entirely accurate because fossilized DNA is often too degraded to analyze, and fossils may not always provide a reliable estimate of age. Option C is not applicable to calibrating molecular clocks. Option D may be used to check results obtained using nucleotide sequences, but it is not a method for calibration.

How Do Scientists Calibrate a Molecular Clock for a Group