The blue-eyed gene for eye color is recessive, meaning that both the eye genes o

Question

The blue-eyed gene for eye color is recessive, meaning that both the eye genes of an individual must be blue for that individual to be blue-eyed. Jo(F) and Joe(M) are both brown-eyed individuals whose mother had blue eyes. Their daughter Flo, who has brown eyes, is expecting a child conceived with a blue-eyed man. What is the probability that this child will be blue eyed? The blue-eyed gene for eye color is recessive, meaning that both the eye genes of an individual must be blue for that individual to be blue-eyed. Jo(F) and Joe(M) are both brown-eyed individuals whose mother had blue eyes. Their daughter Flo, who has brown eyes, is expecting a child conceived with a blue-eyed man. What is the probability that this child will be blue eyed?

Explanation / Answer

SOLUTION:

Jo and Joe have brown eyes and their mother had blue eyes(BB), this means Jo and Joe have Bb gene combination, because they will inherit atleast one gene from her, and father must be either Bb / bb.

Jo (Bb) X Joe(Bb) =>> BB, Bb, Bb, bb

So, FLo has 1/2 probability of being Bb and 1/4 probability of being bb.

Flo is Brown Eyed.

She could either have Bb or bb gene combination.

Her Husband is Blue Eyed.

He must be having BB gene, only then he will have blue eyes.

Flo X Blue-eyed man

The marriage of Flo and her blue eyed husband will result in : ( Bb or bb ) X BB

Here, Flo Bb's probablity =1/2: Flo bb's probability =1/4

Flo Bb X BB =>> BB or Bb (Here again BB and Bb are each formed with equal proabability of 1/2)

Flo bb X BB =>> Bb

HENCE, Probability of blue -eyed child (BB) = 1/2 * 1/2 = 1/4

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