Biology Inheritance / Variation & Genetics MDCAT 2019
PMDC Verified Question 80 of 94
If a carrier haemophilic female (\(X^H X^h\)) is married to a haemophilic male (\(X^h Y\)). What will be the ratio of presence of haemophilia in the children?
A
100% all females and males will be haemophiliac
B
Carrier female 25% haemophilic female 25%, 25% normal male and 25% haemophilic male
C
Females and males both have 25% chances to getting haemophilia
D
Females have 50% chances of getting haemophilia and females will be 100% haemophilic.
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Carrier female 25% haemophilic female 25%, 25% normal male and 25% haemophilic male
Concept:

Haemophilia is an X-linked recessive disorder. We track the X and Y chromosomes through a standard Mendelian cross.

Solution:

  • The cross is between a Carrier Female (\(X^H X^h\)) and an Affected Male (\(X^h Y\)).
  • The Punnett square yields the following 4 distinct offspring probabilities (25% each):
  • \(X^H X^h\): 25% Carrier Female (phenotypically normal)
  • \(X^h X^h\): 25% Haemophilic Female
  • \(X^H Y\): 25% Normal Male
  • \(X^h Y\): 25% Haemophilic Male
  • Option B perfectly lists this 1:1:1:1 distribution.


Why other options are incorrect:

  • The other options present statistically inaccurate percentages that fail to reflect the equal 25% split among the four possible genetic combinations.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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