Nucleotide substitutions occur by mistake in a segment of ribosomal RNA at a constant rate of one substitution every 10,000 years. A biologist has compared the ribosomal RNA of two modern-day species and found that they have six differences in their sequences. How many years ago did these species diverge from a common ancestor? (2 points)
Select one:
a. 3,000 years ago
b. 60,000 years ago
c. 30,000 years ago
d. 6,000 years ago

Question

Nucleotide substitutions occur by mistake in a segment of ribosomal RNA at a constant rate of one substitution every 10,000 years. A biologist has compared the ribosomal RNA of two modern-day species and found that they have six differences in their sequences. How many years ago did these species diverge from a common ancestor? (2 points)
Select one:
a. 3,000 years ago
b. 60,000 years ago
c. 30,000 years ago
d. 6,000 years ago

anonymous · Answer

The answer is 30,000 years.  Each one has diverged from the common ancestor and accumulated it's own mutations which are unlikely to be the same.  So if they differ by 6 mutations from each other, then each one probably differs by 3 mutations from the common ancestor, so it is 3 x 10,000 or 30,000 years.