Joe, who is XY and has classic hemophilia (X‑linked recessive), must have received the hemophilia allele on his single X chromosome from a female ancestor, not from any male ancestor.

For this common textbook‑style question, the classification works like this:

  • His mother – Joe could have inherited the hemophilia gene from her (she must at least be a carrier, unless the mutation arose de novo).
  • His father – Joe could not have inherited the hemophilia gene from him, because fathers give sons a Y chromosome, not an X.
  • His mother’s mother (maternal grandmother) – Yes, she could be the original source; she could have passed a mutant X to Joe’s mother, who then passed it to Joe.
  • His mother’s father (maternal grandfather) – He could not have passed the hemophilia gene directly to Joe, but if he had hemophilia, he would have passed his mutant X to Joe’s mother, making her a carrier; in that indirect sense he can be an ancestral source.
  • His father’s mother (paternal grandmother) – She cannot be the source of Joe’s X, because Joe does not inherit any X chromosome from his father’s side.
  • His father’s father (paternal grandfather) – Cannot be the source for the same reason; Joe’s X comes only from his mother.

If your original problem listed specific relatives in a multiple‑choice or matching format, use this rule to classify them: only individuals on Joe’s maternal line connected to his mother’s X chromosome can be the true source of his hemophilia allele; no male relative can give an affected X directly to him, and nothing on the paternal side supplies his X at all.