***See attached picture***
For any question asking you to draw conclusions about the offspring of two parents, you should always start by making a Punnett Square. This will allow you determine the potential genotypes of the offspring. Here are your steps to making the Punnett Square:
1. Set up a key that states dominant vs recessive alleles and the associated phenotypes/traits. (***see pic***)
2. Determine the genotypes of the parents.
Sometimes this will be given, sometimes you will have to do a little detective work to figure it out. In this case, you have to figure it out using the given info:
- We know that the disorder (cgh) is X-linked and caused by the dominant allele. Therefore, X^D = individual has cgh.
- We know that the father (XY) has the disorder (cgh), so his genotype must be (X^D,Y)
- We know the mother does not have the disorder. Therefore her genotype MUST BE (X^d,X^d). If she even had one dominant allele (X^D) then she would have the disease. Since she doesn't she must have two recessive alleles.
3. Using genotypes of parents, set up Punnett Square. (***see pic***)
4. Make conclusions from Punnett Sqaure. (***see pic***)
Conclusion: After filling out the Punnett Square, you only get two potential genotypes for the offspring: (X^d,Y) and (X^D,X^d).
This means...
Half of offspring would have disorder (X^D,X^d), half of offspring would not have disorder (X^d,Y). Furthermore, all female offspring will have disorder (X^D,X^d), and all male offspring will not have disorder (X^d,Y).
