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

Option B, 60,000 years ago

Step-by-step 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.