Question detail
When performing a genetic cross to determine sex, which of the following represents the correct method to calculate the expected outcomes?
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. Add the total number of offspring
- B. Use a Punnett square
- C. Count only the males
- D. Ignore the females
Answer
The correct option is Use a Punnett square. This answer is correct because it matches the approved learning objective to use direct proportion and simple ratios in sex-determination genetic crosses in the subtopic Sex determination.
Explanation
The correct option is Use a Punnett square. Use a Punnett square is correct because it directly supports the approved learning objective to use direct proportion and simple ratios in sex-determination genetic crosses. This belongs to the subtopic Sex determination within Reproduction, so the explanation must stay tied to that curriculum context. The other options are incorrect because they either do not answer this learning objective, use a vague statement, or move away from Sex determination.
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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