10. The following pedigree shows the pattern of inheritance of a rare trait with

Question

10. The following pedigree shows the pattern of inheritance of a rare trait within the two families. Assume that I-2 and II-1 are not carriers of this trait. a) Is the trait more likely to be dominant or recessive? b) Individuals 111-3 and -4 are expecting their first child. what is the probability that this child will be affected by the trait? 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 trait is more likely to be a recessive trait. This is because, if it were a dominant trait, it would be seen in every generation. A recessive trait would skip generations and not a dominant trait. The probability that the child will be affected by the trait is 50%, considering that the father is a non carrier normal individual of the trait. The couples first child turns out to be affected. Out of four children, 2 children will be affected. Since, the first child is affected, out of the remaining 3 children, there is only one child who will turn out to be affected. Hence, other probability if the next child to be affected is 25%.

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