| Date | May 2016 | Marks available | 1 | Reference code | 16M.1.SL.TZ0.5 |
| Level | Standard level | Paper | Paper 1 | Time zone | TZ0 |
| Command term | Deduce | Question number | 5 | Adapted from | N/A |
Question
Research has shown that the genetic code is not entirely universal. Which research finding has shown this?
A. Some amino acids are coded for by more than one codon.
B. There are differences between the base sequences of genes in different species.
C. In some organisms the genetic code for mitochondria differs from the genetic code for the nucleus.
D. Some codons code for the addition of an amino acid and some code for the termination of translation.
Markscheme
C
Examiners report
Some teachers complained that this question was unfair, as only the universality of the genetic code was expected in the guide. This is true; nevertheless the answer can be deduced and in section 1.5 the guidance does mention that there are some minor changes that have accrued since the origin of species. Most candidates went for answer B, believing that there were differences between base sequences of genes in different species. Although this answer is a true statement, it does not explain why the genetic code is not universal in all cases. The same happens for answers A and D.
