Question 22N.2.HL.TZ0.2a
| Date | November 2022 | Marks available | [Maximum mark: 1] | Reference code | 22N.2.HL.TZ0.2a |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Identify | Question number | a | Adapted from | N/A |
When performing dihybrid crosses with fruit flies (Drosophila), Morgan discovered that his results did not correspond to the expected Mendelian ratios. He explained this by suggesting that there is an exchange of genetic material between chromosomes. The image shows his diagram for three gene loci on a pair of homologous chromosomes during meiosis.
[Source: Morgan, T.H., 1916. Scheme to illustrate double crossing over. [diagram online] Available at:
https://upload.wikimedia.org/wikipedia/commons/0/0e/Morgan_crossover_1.jpg.]
Identify the stage of meiosis shown where exchange of genetic material occurs.
[1]
prophase 1/ first prophase;
The diagram used in this question came from a paper published by Morgan in 1915 and does not show current understanding of the behaviour of chromosomes in meiosis. Nevertheless, 60% of candidates identified prophase 1 as the stage of meiosis when genetic material is exchanged.
