1- First, i m going to explain how the disease is inherited. Like it says in the question, hemophilia's gene is carried on the X chromosome and is recessive. Females inherit two X chromosomes, one from each parent. They are: XX Males inherit one X chromosome from their mother and a Y chromosome from their father. They are XY.
I'll represent with Xᵃ- when the chromosome has the disease's gene and with only an X when that chromosome is normal.
2- If Joe has hemophilia is because the X chromosome that was inherited from the mother, came with the disease. Since men only have one X chromosome, the gene will be expressed. However, this doesn't mean that the mother had the disease, she could be only a carrier with this genotype: XᵃX (there is not enough information to be sure which one is she)
The answers: 3- Maternal grandmother- COULD HAVE INHERITED Like i said before, Joe's mother had a least one X chromosome with the disease's gene, and that came from either her father or her mother( joe's Maternal grandmother). If it came from the grandfather, that means that he was hemophilic. If it came from the grandmother, that means that she was a carrier or also had the disease. There is not enough info to be sure which genotype she has but either way, there is a possibility.
4- Maternal grandfather- COULD HAVE INHERITED Joe's mother had a least one X chromosome with the disease's gene, and that came from either her father( maternal grandfather) or her mother. If it came from the grandfather, we can be certain he was hemophilic.He had the same genotype as joe which is: Xᵃ Y
5- Paternal Grandmother and Paternal Grandfather- COULD NOT HAVE INHERITED. In x-linked recessive diseases, fathers cannot pass it on to their son because they will pass the Y chromosome, not the X. Joe's father gave Joe the Y chromosome and will not pass any X. So, even if Joe's father and his side of the family had hemophilia, that wouldn't matter because either way, Joe will not be receiving any X chromosomes.
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