| Date | May 2015 | Marks available | 1 | Reference code | 15M.1.SL.TZ2.18 |
| Level | Standard level | Paper | Paper 1 | Time zone | Time zone 2 |
| Command term | State | Question number | 18 | Adapted from | N/A |
Question
What causes the presence of three chromosomes 21 in Down syndrome?
A. Crossing over
B. Allele change
C. Non-disjunction
D. Gene mutation
Markscheme
C
Examiners report
In assessment statement 4.2.3 candidates are expected to study crossing over.
