Question

Each of the following answer choices compares a segment of DNA from two related species that diverged from a common ancestor. Assume a mutation rate of one mutation every 60 million years applies to all segments and that a mutation can happen only once at each position in a DNA sequence. Which pair of sequences shows that the two species diverged from their last common ancestor 60 million years ago? GATTCACT and AACTCACA GCGCTTAT and ACGTTTGT TATTCGCG and TATTGCCG TCACTTAA and TCACTCAA

Answer 1

It's the last option ( d ) TCACTTAA and TCACTCAA . This is because it states that every one mutation = 60 million years. This means they have to be exactly identical except for one letter. 

Answer 2

Answer:

The correct answer would be TCACTTAA and TCACTCAA.

It can be correctly explained with the help of molecular clock which is a technique used to determine the time when the two species diverged from a common ancestor.  

It uses the mutation rate to determine the same. Mutation rate is the rate at which a number of mutations take place in a given unit time.

For example, the mutation rate of the given as one per 60 million years, that is, a mutation in one nucleotide takes place in 60 million years.

Thus, if the two species diverged around 60 million years ago from their common ancestor, then the nucleotide sequence of the two species must differ only in one nucleotide.

Hence, TCACTTAA and TCACTCAA form a correct pair of sequences as they differ only in one nucleotide, that is, third last from the right.