Suppose that Smith and bot of his parents have brown eyes (B),
Here, you could have two choices for both parents, BB or Bb
BBxBB = 100% BB all children will have brown eyes.
BBxBb = 50% BB 50% BB all children will have brown eyes.
BbxBb= 25% BB 50% Bb 25% bb 75% of children will have brown eyes, 25% of children will have blue eyes.
but Smith's sister has blue eyes (b).
This means both parents have to be heterozygous dominant Bb
What is the probability that Smith possesses a blue-eyed gene?
If we go back to the offspring probabilities, you have 50% chances of Smith to have the blue-eyed gene.
Suppose that Smith's wife has blue eyes.
The only chance here is that she has bb genes.
What is the probability that their first child will have blue eyes?
If Smith has the blue eye gen the probabilities are
Bbxbb= 50% Bb 50% bb
This means they have a 50% chance of having a blue-eyed child.
If their first child has brown eyes, what is the probability that their next child will also have brown eyes?
Still, 50% because probabilities are always the same in each pregnancy.
