3. The following pedigree shows the pattern of inheritance of a rare trait withi

Question

3. The following pedigree shows the pattern of inheritance of a rare trait within the two families. Assume that I-2 and I1-1 are not carriers of this trait. a) Is the trait more likely to be dominant or recessive? Individuals III-3 and I11-4 are expecting their first child. What is the probability that this child will be affected by the trait? b) c) The couple's first child turns out to be affected by the trait. If they have a second child, what is the probability that this second child will also be affected?

Explanation / Answer

The probability of the III-4 is to be affected=1/4

Hence, the probability that the first child will be affected is=1/2x1/4=1/8

                                    OR

Assume that the III-3 is carrier for the trait

So, cross between the III-3 (XdX) and III-4 (XdXd) gives the following offspring

Probability of the affected child=2/4 or 1/2

Probability of the carrier child=2/4 or 1/2

Then the probability that the first child will be affected is 1/2 or 0.5

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