Humans and chimpanzees diverged about 6 million years ago. If 12 nucleotide substitutions have occurred between human and chimpanzee lineages in a sequence of mitochondrial DNA, and 36 have occurred between humans and gibbons, humans and gibbons, according to the molecular clock, separated _______ million years ago.
A) 2
B) 6
C) 12
D) 18
E) 36

Question

Quizplus · Accepted Answer

According to the molecular clock, the number of nucleotide substitutions in a DNA sequence is proportional to the time since the lineages diverged. Therefore, to calculate the time since humans and gibbons separated, we can use the ratio of nucleotide substitutions between humans and gibbons to that between humans and chimpanzees:

36 substitutions / 12 substitutions = x million years / 6 million years

Solving for x, we get:

x = (36/12) * 6 = 18

Therefore, humans and gibbons separated 18 million years ago.

Humans and Chimpanzees Diverged About 6 Million Years Ago