QUESTION 78 (6 marks)
A person with blood group A and a person with blood group B have a child with blood group O. For ABO inheritance, and are codominant and both dominate .
a) Determine both parents’ genotypes. [2 marks]
b) Use a genetic cross to predict the possible offspring blood groups and their probabilities. [2 marks]
c) Determine the probability that their next two children are one AB and one O, in either order. [2 marks]
Practice marking scheme
Answer
a) Iᴬi and Iᴮi. b) A, B, AB and O each have probability 1/4. c) 1/8.
Working
An O child is , requiring each parent to supply . Thus the A parent is and the B parent is . Their offspring genotypes are , , and , each with probability . The specified two-child event can occur AB then O or O then AB, giving .
Marking criteria
- States Iᴬi for the A parent. [1 mark]
- States Iᴮi for the B parent. [1 mark]
- Shows the four genotype outcomes. [1 mark]
- Gives each blood-group probability as 1/4. [1 mark]
- Includes both possible orders. [1 mark]
- Calculates 1/8. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.