Final answer:
Scientists calibrate a molecular clock by graphing nucleotide differences against evolutionary branch points from the fossil record to estimate the divergence time of species. By analyzing DNA sequences and protein data alongside the fossil evidence, scientists can trace evolutionary history with greater accuracy. The correct option is D.
Step-by-step explanation:
Scientists calibrate a molecular clock for a group of organisms with known nucleotide sequences by analyzing the number of nucleotide differences and comparing them against key evolutionary events. The correct answer to the question is D.
They graph the number of nucleotide differences against the dates of evolutionary branch points known from the fossil record. This method relies on the assumption that mutations in DNA accumulate at a constant rate over time for a given gene or DNA region.
Thus, greater differences in DNA suggest a longer time since two species have diverged from their common ancestor. Scientists use this comparative analysis alongside fossil evidence to refine the calibration of the molecular clock.
By understanding the mutation rate and utilizing molecular evidence from both DNA sequencing and protein data, researchers can construct phylogenetic trees that trace the evolutionary history of organisms. This approach not only confirms classifications based on physical morphology but also uncovers previous classification errors.
As molecular biology advances, so too does the accuracy of our evolutionary timelines and the resolution of our understanding of the relatedness between species. The correct option is D.