Question

If mutations occur at random, and changes to 1st or 2nd "letter" of a codon usually changes the amino acid coded for, but changes to the 3rd "letter" rarely do, roughly what % of mutations should be synonymous? Second АТ G UUU Phe UCU Ser UAU Tyr UGU Cys U 0 C | Phe UCC Ser UAC Tyr UGC Cys C Leu UCA Ser UAA Stop UGA Stop UUG Leu UCG Ser UAG Stop UGG Trp G CUU Leu CCU Pro CA U His CGU Arg CUC Leu ССС Pro C A C | His CGC Arg C A Leu CCA Pro CAA Gin CGA Arg CU G Leu CCG Pro CAG Gin CGG AUU lle ACU Thr AU Asn AGU AUC lle ACC Thr AAC Asn AGC Ser AUAlle ACA Thr AAA Lys AGA AUG Met ACG Thr AAG Lys AGG GUU Val GCU Ala GAU Asp GGU GUC Val GCC Ala GAC Asp GGC GUA Val GCA Ala GAA Glu GGA GIV GUG Val GCG Ala GAG Glu GGG Gly A. 5% B. 10% C. 25% D. 50% First Arg Ser Ducoucoucouco Third Arg Arg Coded by 6 codons Coded by 4 codons Coded by 3 codons Coded by 2 codons

Answer 1

Synonymous mutations are those that change the triplet code of the amino acid without changing the amino acid that it codes for.

Codons generally have a wobble position in the 3rd base, meaning that changing it would not lead to any effect and the amino acid would remain the same. Leu, Arg, Ser are coded by 6 codons that are determined by the 1st and 2nd bases irrespective of the base present in the 3rd position. About 50% mutations could be synonymous, since out of 64 total codons present, at least more 35 such amino acid codons are present that have 3rd base degeneracy. Mutations occuring here would be synonymous.