Question detail
In a population where 1 in 4 males are affected by an X‑linked recessive disorder, what proportion of the offspring of an affected male and a carrier female will be affected?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Reproduction
Question
In a population where 1 in 4 males are affected by an X‑linked recessive disorder, what proportion of the offspring of an affected male and a carrier female will be affected?
Answer
An affected male is X^dY and a carrier female is X^dX^N. Offspring are X^dX^N (female) or X^NY (male). Only the female can be affected, so 1 out of 2 offspring, or 50 %, will be affected.
Explanation
The answer demonstrates use of direct proportion and simple ratios in a sex‑determination cross, correctly identifying the only affected sex and calculating the proportion.
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.
Related flashcards
Flashcard 1 of 5
Related practice questions
Question 1 of 5
Choose an answer, get feedback, then move sideways through the set.