Question

In a form of early-onset Alzheimer disease caused by a mutation on chromosome 14, A is changed to T at the first position of codon 146, which substitutes leucine for methionine. This mutation is a _______  and is _______ 

Select one: 

a. Transition; missense 

b. Transversion; nonsense 

c. Transversion; missense 

d. Transition; nonsense

Answer 1

Missense mutations are mutations where a single amino acid is substituted for another amino acid. This may cause the protein to have altered function. Nonsense mutation will lead to formation of stop codon and therefore premature termination of protein synthesis. As leucine is replaced by methionine, this is missense mutation.

In DNA, adenine and guanine are purines while thymine and cytosine are pyrimidines. When purine is changed it purine or pyrimidine to pyrimidine, it is a transition. If purine is changed to pyrimidine or vice versa, it is transversion. As adenine (purine) is replaced by Thymine (pyrimidine), it is a transversion.

Right Choice; c. Transversion; missense.