The figure below shows a pedigree for a rare trait in humans. Affected individua
ID: 194515 • Letter: T
Question
The figure below shows a pedigree for a rare trait in humans. Affected individuals are indicated by the filled-in symbols. The woman II-2 is pregnant, with II-3 being the father. Her unborn child is represented by the “?”.
Q1.Is the trait inherited as a dominant trait or as a recessive trait? What is the best evidence for your answer? (6)
Q2. What is the probability that both II.2 and II.3 are heterozygous for the trait? (6)
Q3. What is the overall probability that the child will be unaffected by the trait and be a girl? (6)
4 4 3 3 2 2 2 1 1Explanation / Answer
Ans 1 The trait is X linked recessive because it alleared in II 1 while showing no manifestation in parental generation. If it were dominant then it has to be present as an affected trait in the parental generation. The parents were the carriers and II A is homozygous recessive to the trait. Moreover the X from parent in 3 has to be present in 4 if it was dominant because in girl child each X comes from each parent.
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