Cause genetics totally work like that.
Not likely but they can.
No, not unless there is a mutation.
She needs blond on both sides of her family in order to get it to work, just like how red requires it as well, and blue eyes. Bruce Lee could have a son who was blond at birth precisely because he was quarter German.
EDIT: Not that I mind Shou stretching the reality of the situation, but I find it interesting he adds in that the blond hair is silkier and softer, which in my experience is true.
Genetic mutation isn't "genetics"? :P
Hair, eye colour etc are polygenic traits so you can't just go and apply Mendelian rules to them. Recent European intermingling isn't necessary for blonde hair traits to surface either, there are/were Asiatic ethnicities with light hair and eyes. Basically "life finds a way"...
Polygenic just mean that the genes in question work in an additive way, rather than a dominant and recessive way. Which, if anything, should make Ran's light hair even more unlikely.
Your (actually you probably already know this but I'm going to say it anyway) hair colour is determined by melanin or more specifically, by a type melanin called eumelanin. As we established above, eumelanin (or more specifically the genes which control its production) operates on additive principles, rather than Mendelian ones. Now lets say there are six genes which determine hair color, that Ran gets her Finnish ancestry from her mothers side of the family and that these genes are represented as Cc, with C representing high levels of eumelanin production-and thus dark hair-and c representing lower levels, which should obviously lead to lighter hair.
So her grandfather is presumably a light haired Finn with the genes CCcccc or Cccccc, while her grandmother was a dark haired Asian woman, who should have the genes CCCCCC.
Now Ran's mother would receive half of each of these sets. Most likely she would get something like CCCccc or CCCCcc, giving her intermediate brown hair. As you have probably already figured out, this means that if Ran's mom married a Japanese man (as she presumably did, as Ran is supposed to be 1/4 Finnish) then the best possible combination Ran could have is CCCccc like her mother, giving the same intermediate brown hair.
But what if Ran's grandmother had unusually light hair for a Japanese women, something like CCCCcc and her daughter, Ran's mother, inherited Cccccc? Well then Ran's mom likely did have blonde hair but its still unlikely Ran would have blonde hair also as Ran's father was still Japanese meaning Ran would once again end up with, at best, CCCccc, as its unlikely he too would have such light hair, as any hair colour other than "pitch black" is pretty rare amongst East Asians, especially amongst men (men of any ethnicity typically have darker skin and hair colours than their female counterparts). However, if he did have light hair color, it is possible that Ran could end up with something like dirty blonde or at the very least very light brown hair.
So, long story short, Ran being blonde, while possible, is extremely unlikely.
As for your statement of some Asian ethnicities having blonde hair, you are correct but said ethnicities are located in the Middle East/West Asia and central Asia, not East Asia like Japan. There are Melanesian cultures who have blonde hair as well but said blondness comes from entirely different genetics, more specifically, from an amino acid change in a specific gene which does not exist in any other ethnic group on the planet.
last edited at May 12, 2015 3:39PM