Question

Now consider a single base mutation in a codon for leucine that creates a codon for phenylalanine. A true reversion changes the phenylalanine codon back to a codon for leucine. Which of the following leucine codon(s) could be mutated once to form a phenylalanine codon, and then mutated at a second site to restore a leucine codon? Select all that apply. (Note that two different positions in the codon must be mutated.) Select all that apply. (Note that two different positions in the codon must be mutated.)

CUU

CUC

CUA

UUG

UUA

CUG

none of these codons

Answer 1

Answer:

CUU, CUC, UUG, UUA

Explanation:

Following codons result in leucine amino acid : UUA, UUG, CUU, CUC, CUA and CUG

Following codons result in phenylalanine amino acid : UUU and UUC

• CUU : If C is mutated to U, result will be UUU which is phenylalanine codon. U at third position can be mutated to A which will form UUA which us again codon for leucine.
• CUC : If C at first position is mutated to U, phenlyalanine codon UUC will be formed. C can be mutated to A to form leucine codon UUA.
• UUG : If G is mutated to U phenylalanine codon UUU will form. U at first position can be mutated to C to form leucine codon CUU.
• UUA : If A is mutated to U phenylalanine codon UUU will form. U at first position can be mutated to C to form leucine codon CUU.