Using this information:
Answer these questions:
The pedigree provided looks complicated and messy. But it's really just squishing together a pedigree for hemophilia and a pedigree for albinism. Personally I think it's silly and annoying to cram so much information into pedigrees this way, because they just end up looking confusing and are hard to follow.
So... the first thing I did was to make separate pedigrees!
One for hemophilia:
And one for albinism:
Next, I figured out the genotypes for the hemophilia pedigree. Remember: squares are males, and circles are females. Hemophilia is X-linked, so the genotype options won't be the same for males as they are for females (because males are hemizygous).
We were also told that hemophilia is a recessive disorder:
Figuring out the rest is like solving a puzzle (it actually reminds me of sudoku for some reason...). Clara got an H allele from her mom, and her dad only has a h, so Clara's genotype has to be Hh.
We don't have enough information to tell whether Clara's mom's genotype is HH or Hh.
Charles has a brother with genotype hY. He got the Y from his dad (because his mom doesn't have one), so he had to have gotten the h from his mom. So, Charles's mom's genotype has to be Hh.
We don't have enough information to tell whether Charles's sister's genotype is HH or Hh.
Now, genotypes for the albinism pedigree. Albinism is an autosomal (i.e., not sex-linked) recessive condition, so we can ignore sex for this part.
Blue shapes (circles and squares) have albinism, so they have to have the genotype aa.
Anyone with the genotype aa had to get one a from each parent
White shapes have to have at least one A
Clara, Charles, and Charles's brother could be AA or Aa
It'd be really nice to know the genotypes of Clara and Charles, but we can't be sure based on the pedigree. They each have a 2/3 probability of being heterozygous, and a 1/3 chance of being homozygous dominant. They can't be homozygous recessive because we already know they don't have albinism.
Probability:
What's the probability that Clara and Charles have a son with hemophilia?
For this part we only have to look at the hemophilia pedigree. The probability that they have a son with hemophilia is the probability that their child has the genotype hY
...which is 1/4.
What's the probability that Clara and Charles have a daughter with albinism?
That's the probability that they have a daughter with genotype aa. In order for Clara and Charles to have a child with that genotype, Clara and Charles must each have an a allele. The probability that Clara has an a allele is 2/3. The probability that Charles has an a allele is 2/3. So, the probability that Clara AND Charles have genotype Aa is (2/3) x (2/3) = 4/9. If both parents are heterozygous, then the probability of their child having the genotype aa is 1/4. So, the probability of Clara and Charles having a child with albinism is (4/9) x (1/4)= 1/9. Their child has a 1/2 chance of being a girl, so the probability that they have a girl with albinism is (1/9) x (1/2) = 1/18.
