Joe, who is male (XY) and has classic hemophilia (an X-linked recessive disease), must have inherited the hemophilia gene on his single X chromosome from his mother, because males inherit their X chromosome from their mother and their Y chromosome from their father
. Classifying each relative based on whether Joe could have inherited the hemophilia gene from them:
- Maternal Grandfather: Yes, indirectly. If Joe's maternal grandfather had hemophilia, he would have passed his affected X chromosome to Joe's mother, who could then pass it to Joe. So Joe could have inherited the gene through his mother from the maternal grandfather
- Maternal Grandmother: Yes. She could have passed the affected X chromosome to Joe's mother, who then passed it to Joe
- Paternal Grandmother: No. Joe's paternal grandmother passes her X chromosome to Joe's father, but Joe inherits the Y chromosome from his father, not the X. Therefore, Joe cannot inherit the hemophilia gene from his paternal grandmother
- Paternal Grandfather: No. Joe's paternal grandfather passes his Y chromosome to Joe's father, and Joe inherits the Y chromosome from his father, so no X-linked gene from the paternal grandfather can be passed to Joe
In summary:
Relative| Could Joe have inherited the hemophilia gene?
---|---
Maternal Grandfather| Yes (indirectly via mother)
Maternal Grandmother| Yes
Paternal Grandmother| No
Paternal Grandfather| No
This classification aligns with the principles of X-linked recessive inheritance, where males receive their single X chromosome from their mother, and fathers cannot pass X-linked traits to their sons
