Question 19N.2.HL.TZ0.2
| Date | November 2019 | Marks available | [Maximum mark: 4] | Reference code | 19N.2.HL.TZ0.2 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Deduce, Identify, State | Question number | 2 | Adapted from | N/A |
The diagram shows one of Thomas Hunt Morgan’s crosses of Drosophila in the early 20th century.
State the type of inheritance shown.
[1]
«gene/autosomal» linkage ✔
Reject sex linkage
Identify the recombinants.
[1]
grey vestigial and black normal ✔
Accept Ggvv and ggVv or alternative acceptable upper/lower case genotypes.
The chi-squared value was calculated as shown. Deduce, with reasons, whether the observed ratio differed significantly from the expected Mendelian ratio.
[2]
a. yes/observed ratio did differ significantly «from the expected Mendelian ratio»
OR
expected ratio is 1:1:1:1 / 575 of each type / 25 % of each type ✔ Correct ratio not needed in first alternative of mpa
b. 3 degrees of freedom ✔
c. critical value is 7.815 «at the 5 % level / 11.345 «at the 1 % level» ✔ Accept mpc if candidates indicate the critical value of chi squared by circling it.
d. chi-squared value «of 1002.6» exceeds the critical value ✔
Allow other levels of significance as long as the critical value is correctly stated for the chosen level.
