Continue to assume that the same four individuals in the pedigree are albinos, and calculate the probability of the albino trait appearing in the offspring if the following cousins and second cousins should marry and reproduce: a. 4 x 5 b. 6 x 10 c. 7 x 14 d. 2 x 10
For a specific example, you might assume that four members of this pedigree are albinos: the woman in the first generation, her second daughter (the mother of individuals 5, 6, 7, and 8), and individuals 4 and 11 in the third generation. Now, assume that you are a genetic counselor and that individuals 6 and 12 in the third generation of this pedigree come to you and ask, “What is the probability that if we marry and have a family, an albino child will be born to us?”
The counselor must determine the probability that individuals 6 and 12 are heterozygous carriers of the recessive gene for albinism. The counselor must also consider the probability of two heterozygous carriers producing a homozygous recessive child. First of all, the mother of individual 6 is an albino (cc), which means that 6 must be (probability = 1 or 100%) a heterozygote. The father of individual 12 must be heterozygous (Cc) since his mother is an albino. Although individual 12 is not an albino, he has a ½ chance of being heterozygous, depending on which allele (C or c) he inherited from his father. Finally, two heterozygotes (Cc x Cc) have a ¼ chance of producing an albino (cc) child. The genetic counselor may advise individuals 6 and 12 that if they were to have children, the probability of their having an albino child will be 1 x ½ x ¼ = ⅛. This is the probability that the three independent events will occur simultaneously.
A slightly more confusing situation arises in determining the probability that an unaffected child of two known- heterozygous parents is itself heterozygous. For example, in the pedigree shown, we know with certainty that the parents of individual 10 must be heterozygous. The question, then, is “What is the probability that one of their
Continue to assume that the same four individuals in the pedigree are albinos, and calculate the probability of the albino trait appearing in the offspring if the following cousins and second cousins should marry and reproduce:
a. 4 x 5
b. 6 x 10
c. 7 x 14
d. 2 x 10
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