B) The figure below shows a pedigree for a rare trait in humans. Affected indivi

Question

B) 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.ls the trait inherited as a dominant trait or as a recessive trait? What is the best evidence for your answer? (6) 02. What is the probability that both II.2 and l1.3 are heterozygous for the trait? (6) 03. What is the overall probability that the child will be unaffected by the trait and be a girl? (6) 1 2 4 4

Explanation / Answer

1) it is a recessive trait.

As in 1st Gen both the parents are normal but the offspring is affected. Indicating that both of them are carriers. The carriers are not affected hence it is a recessive trait.

2) as from the answer 1 we know that both the parents are heterozygous for the trait so Aa x Aa

Gives AA, Aa, Aa and aa

So there is 50% chances that ii2 is heterozygous for the trait.

In gen1 parent 3 and 4

3 is affected so he has aa

4 is healthy and none of the offspring is affected so she is AA

AA x aa= Aa, Aa, Aa, Aa

So in 2nd Gen. 3 will 100% be heterozygous

Answer 3)

2 can be AA or Aa

3 is definitely Aa

So if 2 is AA then the child will be normal

If 2 is Aa then there is 25% chance that the child will be affected.

And there is always 50% chances that the child will be a girl.

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