Question

Suppose an error in transcription causes threonine (Thr) to be incorporated into the variable region of an antibody instead of arginine (Arg). Which of these could describe the error
ACG was transcribed instead of AGC.
ACC was transcribed instead of ACA.
AGA was transcribed instead of AGG.
ACA was transcribed instead of AGA.

Answer 1

ACG was transcribed instead of AGC.

Answer 2

Threonine is an aminoacid that can be coded with these 4 codons: ACT, ACC, ACG, ACA.

Arginine can be coded with these codons: CGT. CGC, CGG, CGA, AGA, AGG

The answer is ACA was transcribed instead of AGA.

 From those options this is the only one that works.
AGA would code for Arg but due to the error, it was transcribed as ACA and became Thr.