there are 4 eumelanin genes that determine hair color. you get 4
copies of each gene from your mother and 4 from your father giving
you a total of 8.
If one of these hair color genes is ON, we'll represent it with H and if it is OFF, we'll represent it with h. Using this system, someone with very black hair would be HHHHHHHH and a blonde person would be hhhhhhhh.
your kids will get 4 copies of the gene from each of you and there is no dominance per say---they add up to give a hair color. If each of you contributed only h's, then you would get a blonde haired kid like your son with a genotype of hhhhhhhh. Your daughter got more H's than h's (perhaps HHHHHhhh) and so has dark hair.
There are nine possible shades between blond and black hair. There are three possible states of red hair (no, yes, very much so). That combines to 9*3=27 possible hair colors on the genotype level. Of those, 18 are various shades of red, 9 are shades that are not red.
Yep, redheads come in a wider variety than everyone else! What can I say to that? By nature's own design, we (redheads) are more original than anyone else!
Think about it next time you feel like making fun of redheads. Besides, never forget, for all you know, you may be a redhead and not even know it!
(source off internet, by Taras Brudnyy)