Possible basically butchers recessive genes(and dominant too if you want to nitpick likely vs possible). Anything is possible if both parents carry a recessive gene. You might as well put blue hair in there because "it's possible if someone in the family had it before". It's a very simplistic explanation of inheritance. It should at least include the grandparent generation to demonstrate how and where recessive genes work. This isn't really a "guide" - barely an infographic.