Lilys grandparents

[Balac Marija]

No: HPFGUIDX 109993

"kmcbears1" karen at dacafe.com wrote: 

IMO JKR wants us to know that Lily and Petunia are Muggles.  Harry is 
a half-blood as is Voldemort. IMO this is a crucial part of the story.

If Lily's Grandparents are Muggles then we must go back 6 or 7 
generations to find magical blood. 

 

 

Not exactly:

If we apply the rules of genetic inheritance, we must presume that being a witch or a wizard is a dominant characteristic (D). 

In that case, purebloods would be DD. 

Therefore, an old wizard family would follow this pattern:

parents:         (mother)  DD ---- (father)  DD
children:       all 100% DD purebloods.


If a pureblood married a muggle (dd, where d is recessive) we’d have these possibilities:

parents: (m)  dd ---- (f)  DD
children: dD dD Dd Dd  all halfbloods

Mudbloods could be explained only by genetic mutation (not something unnatural).  That's why Lily didn’t need to have any magical ancestors. 

For Harry to be a halfblood (Dd), she had to be (Dd). James must have been pureblood (DD), since he was from an old wizarding family (if I’m not mistaken).

(Lily)   Dd ----  (James)   DD
children: DD DD dD dD    

It even would have been possible for Harry to be a pureblood.

Did I miss any categories?
 
Maya

P.S. My question is, why muggle parents would be so pleased to have a witch in a family?