Andrew did a mutant screen with his favorite bacterium that he used for marine phage hunting. He identified three base-substitution mutations on the bacterial recA gene: Mutant A: A base substitution occurred, which changed T to C, and consequentially abolished transcription of the recA gene.
Mutant B: A base substitution, which changed codon 2 from ACC to ACT, which did not change encoded amino acid.
Mutant C: A base substitution occurred, which changed codon 3 from TCA to a stop codon TGA.

Based on the above info, which of the mutants would still have functional RecA protein?

a. Mutant B
b. Mutant A
c. Mutant C

a. Mutant B

Explanation:

This question is describing a kind of mutation called SUBSTITUTION MUTATION, in which one or more nucleotide base is replaced by another in a sequence. In this case, the base-substitution mutations occcurs in the bacterial recA gene sequence.

However, base substitutions can be grouped into three based on the different results it yields namely: missense mutation, nonsense mutation, silent mutation.

- In Mutant A: A base substitution occurred, which changed T to C, and consequentially abolished transcription of the recA gene. This is an example of missense mutation because it changes the sequence.

- In Mutant B: A base substitution, which changed codon 2 from ACC to ACT, which did not change encoded amino acid. This is an example of silent mutation because it does not alter the sequence of the gene.

- In Mutant C: A base substitution occurred, which changed codon 3 from TCA to a stop codon TGA. This is an example of nonsense mutation because it leads to a STOP CODON.

According to the question, MUTANT B would still have functional RecA protein because it doesn't change the encoded amino acid sequence, which will still lead to the production of the RecA protein.

i'd say that the moon rock is about 2.2 billion years old.