Its been discussed that Fry is his own Grandfather, and thus his own Father's Father,
But here's what i don't get: If Enos is meant to be the 'father' of Yancy Sr., why is Fry's Mother the one with the orange and spiked hair?
1) It could be just coincidence. Philip's mother had to have some
natural color and characteristic shape. They might
have been 'orange' and 'spikey' (respectively) just by chance. (Actually, I believe this IS the case with Enos.)
2) Genetically it is much
more likely to have come from his mother's genes. As far as genetic material goes...
Philip's mother's mother = A,
Philip's mother's father = B,
Philip's father's mother = C,
Philip's father's father = D, and hence
Philip's mother = (A+B)÷2,
Philip's father = (C+D)÷2, and (in theory)
Philip = (A+B+C+D)÷4
But from Roswell that end's well
we know that...
D = Philip
Thus (A+B+C+D)÷4 = D
Rearranging and solving for D (i.e. Philip) gives...
Philip = (A+B+C)÷3
Yancy Sr. = (A+B+(4×C))÷6
As you might expect in time-loop paradoxes Philip has contributed no 'new' genetic material to himself or to his father/son. All of Philip's and Yancy Sr.'s genetics come from Philip's other grandparents.
So, Philip's orange, spikey hair either comes from his mother's side of the family (A or B) or comes from Mildred (C).
But Mildred is shown having long brown hair and her son's (Yancy Sr.) hair is even darker although somewhat spikey (in a Bart Simpson sort of way). Hence it seems likely (but not completely certain) that Mildred is NOT the source of Philip's hair color and style and therefore Philip's mom is.
Thus to offer a more scientifically plausible (and visible) solution I suspect that they deliberately made Philip's mother's hair a similar color and style similar to his and hoped the fans wouldn't twig as to why until they had the benefit of hindsight.
Personally, I think Enos' hair is a red-herring (no pun intended (at least by me)).
And another thing: Yancy Sr. mentioned to Yancy jr. he was named Yancy, like his father before him, all the way back to 'Minute-man' Yancy Fry. If Enos was meant to be his dad... why wasn't he named Yancy?
I think you'll find that Yancy Sr. starts from his grand
father, not his father.