[thedoc (OP)]

Margo Riley  asked the Naked Scientists:
   
Hi Chris
 
I have a "mallen's streak" a pure grey streak of hair and the rest is just plain brunette.  My mother has one in the exact same place and my 15yr old son is developing the same in the same place.  Obviously we've inherited this somewhere along the line but what causes this?  Just one grey streak.  We all developed this at a young age.
 
Kind regards
Margo

What do you think?

[algatto]

I can understand why hair would be grey in a particular patch of skin but I cannot understand why the location of that patch would be the same in successive generations.