Answer:
1/4
Explanation:
Person 5 marries a man who does not have cataracts and produced children in which some have cataracts and others do not have. It thus means that person 5 is affected for the disorder and the man she married is a carrier (although phenotypically normal) of the disorder.
Assuming the cataract disorder allele is represented by c, unaffected version of the allele will be C. Person 5 will have the genotype cc while the man she married will have the genotype Cc.
Crossing the two:
Cc x cc = Cc, Cc, cc, cc
50% of the offspring are phenotypically free from cataracts while 50% have cataracts.
The probability of having a cataracts infected child is thus 50% or 1/2. This probability remains the same irrespective the number of child they have already produced.
The probability of producing a girl for every marriage is 50% or 1/2.
Hence the chance that their next child will be a girl with cataracts = probability of their next child being a girl and the probability of their next child having a cataracts.
= 1/2 x 1/2 = 1/4
<em>The chance that their next child will be a girl with cataracts is 1/4.</em>
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