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Originally Posted by poppy  From doing biology at school - this is my attempt to explain it! There is probably a genetic scientist on this forum who his going to correct me now!
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This is exactly right and you explained it very well. But there's another kicker here. For many genetic traits there isn't just two alleles B (Brown eye) and b (blue eye), but quite a few different alleles... so the punnet square gets quite complex (if you are trying to document it this way.)
My father has brown eyes (dominant), and my mother has blue (recessive) and their three kids are all blue eyed, so we know that my father carries at least ONE recessive non-brown allele for eye color.
As far as the red hair thing goes... hair color is made up of two types of chemicals- eumelanin (brown and black melanins) and phaeomelanin (red and yellow melanins) produced by melanocytes (or 'color cells').
When you have more of one, say eumelanin - you have brown hair (but some very dark haired people have some red tinge to their hair in the sun... this means they have some phaeomelanin too. All of one chemical or the other produces black or red hair depending on the chemical. And as we age, these color proportions may change. My two very blonde (as young children) brothers, now have very dark hair as adults. So the genetics of hair color are QUITE a lot different than normal alleles...
I have red hair. Though both my parents have dark hair, they both have red tinges to their hair in the sun (in fact, my almost black haired father grows a dark redish beard if he let his whiskers grow). My daughter does not have red hair, though she too has some red tinges in there in the sun...
Now, my DH has black hair. I've not noticed any red in his hair, though he grows blonde whiskers in his beard... and with my fairly dominant red hair, he thinks we'll be making a red haired daughter. I'm guessing no but I've been wrong before
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