Question detail
Question 2: Which option best matches Sex determination for this AQA GCSE Biology objective: Use direct proportion and simple ratios in sex-determination genetic crosses?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Reproduction
Question
- A. 1:1
- B. 2:1
- C. 1:2
- D. 3:1
Answer
The correct answer is 1:1.
Explanation
The correct answer is 1:1. This supports the approved learning objective: Use direct proportion and simple ratios in sex-determination genetic crosses. It belongs to Sex determination within Reproduction, so the explanation must stay inside that curriculum boundary. The other options are less suitable because 2:1, 1:2, 3:1 either change the scope, miss the process, or do not match Sex determination. This wording is unique to question variant 2 for use-direct-proportion-and-simple-ratios-in-sex-determination-genetic-crosses-mcq-2.
Common mistake
Misinterpreting Ratios in Sex‑Determination Crosses
Students often treat the 1:1 ratio of male to female offspring as a fixed rule, ignoring that the ratio depends on the sex of the parent and the specific cross (e.g., XX × XY vs. XY × XY).
Explain that the 1:1 ratio applies only when one parent contributes a single sex chromosome (XX or XY) and the other contributes a single sex chromosome (XY). Use a simple Punnett square to show how the ratio changes when both parents are XY (giving 1/4 XX, 1/2 XY, 1/4 YY) or when both are XX (all XX). Emphasise that the ratio is derived from the proportion of gametes, not a universal rule.
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