Question

Q1. Why is the SSU rRNA gene used as a molecular clock? Choose two reasons out of the following three:

A) It evolves slowly

B) It is an essential gene

C) It is easily horizontally transferred

Q2. Which of the following observations is usually required to know that two bacteria are members of the same species? Pick two answers out of the three.

	A) average nucleotide identity greater than or equal to 90%
	B) SSU rRNA similarity greater than or equal to 95%
	C) shared ecotype similar at greater than or equal to 95%

Answer 1

1) It evolves slowly and it is an essential gene - SSU rRNA are used in studying evolutionary relationships among organisms. They are present in all organisms and are essential for an organism. Because essential, it is coserved and evolve slowly.

2) Average nucleotide identity greater than or equal to 90% and SSU rRNA similarity greater than or equal to 95% - The Average nucleotide identity (ANI) of orthologs should be greater than or equal to 90% and the SSU rRNA similarity should be greater than or equal to 95% to consider two different organisms are of same species. Many researchers expect atleast 95% ANI and 97% SSU rRNA similarity to consider two organisms under the same species.