Question

I don't understand this!
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 modern0day 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

Answer 1

Each on diverged from the common ancestor and has its own accumulated mutations. If they have six differences each it would be 10,000 years per one mistake giving you a total of 60,000 years ago. 

Answer 2

Answer:

Option B, 60,000 years ago

Explanation:

It is given that the rate of substitution is one substitution per $10,000$years

Thus, starting from the base year

Number of substitution after $10,000$years $= 1$

Number of substitution after $20,000$years $= 2$

Number of substitution after $30,000$years $= 3$

Number of substitution after $40,000$years $= 4$

Number of substitution after $50,000$years $= 5$

Number of substitution after $60,000$years $= 6$

Thus, it is clear that $6$ substitution or changes will occur in $60,000$years.

Thus, option B is correct.