Genetics Problem -- Colourblindness is a recessive X linked trait

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Discussion Overview

The discussion revolves around a genetics problem related to colorblindness, which is identified as a recessive X-linked trait. Participants are calculating probabilities concerning the inheritance of colorblindness in offspring, specifically focusing on the probabilities associated with daughters, blood types, and normal vision.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates a probability of 3/32 for a daughter being colorblind, considering factors such as blood type and vision.
  • Another participant challenges this calculation, suggesting that the overall probability of colorblindness should be 3/4, but emphasizes the need to adjust for the child's gender.
  • A different participant recalculates the probability as 1/16, factoring in the probability of a daughter and the likelihood of her being colorblind.
  • One participant suggests using a Punnett square to clarify the probabilities related to gender and colorblindness.
  • Another participant arrives at a probability of 1/8, correcting their earlier assumption about the father's genotype.
  • A later reply confirms the last calculation as correct.

Areas of Agreement / Disagreement

Participants express differing views on the correct probabilities, with no consensus reached on the final answer. Multiple competing calculations and interpretations of the problem remain present.

Contextual Notes

Some calculations depend on assumptions about the genotypes of the parents, and the discussion reflects uncertainty in the application of probabilities related to X-linked traits.

TytoAlba95
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Homework Statement
Colourblindness is a recessive X linked trait. A couple, who are both blood type A and with normal vision have a son who is blood type O and colourblind. What is the probability that their next child would be a daughter and with blood type O and normal vision?
Relevant Equations
a. 1/2
b. 1/4
c. 1/8
d. 1/16

Ans is a.
I'm getting 3/32.

P= Probability of a daughter x Probability of O blood type x Probability of Normal vision
= 1/2 x 1/4 x 3/4
= 3/32
 
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A looks like the wrong answer to me.

3/4 is the correct overall probability of colorblind ness, but you need to account for the fact you've already included the probability that the child is female. Given that the child is female, what is the probability that she will be colorblind?
 
P= Probability of a daughter x Probability of O blood type x Probability of Normal vision girl
= 1/2 x 1/4 x 1/2
= 1/16

Thank you :)
 
Still not correct. It may be helpful to write out a Punnet square for gender and colorblindness.
 
243991

Therefore P= 1/8.
I was taking the father as XcY, which actually should be XY.
 
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Correct!
 
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