My parents/uncles/cousins/sister have brown hair. My wifes side are white/blond and I have a white/blond son. If brown is the dominant colour how do we explain this? And before anyone suggests it, I have no worries about the milkman etc!
Be sure to include a link to Cecil’s column: What are dominant traits? Does it involve leather?
The answer is easy. Since your son is blonde, his genotype is WW, so he must have gotten a W from you and a W from his mother. If his mother is WW as well, that only makes sense. But in your case, we can’t tell if you’re BW or BB by looking at you. In this case, however, we know you must be BW, and you must have passed on the W to your son instead of the B.
:cough: Oversimplification :cough:
Hair color is a funny thing. There is a wide range of colors, & you often get intermediate colors instead of dominance. Then there are the towheaded (very fair-haired) kids that grow up to have much darker hair. This may be what your son is. Not all blonds are really WW.
Yes, but it is a good description of the basic genetics of how dominants and recessives are passed on.
lionscroft, with simple traits, the genotype is determined by the contributions from each parent. You get one half from the father, one half from the mother. A dominant trait is one that expresses with only one half the pair. A recessive will only express if it has both. This is because the dominant will express over the recessive if you have one of each.
I am a 35 yo male. I was blonde until puberty. Since then my hair got steadily darker until it reached a sandy brown. Neither one of my parents had blonde hair, but I’ve been told that the same thing happened to my father.
By the way, what is the correct spelling of “blonde”? I remember reading somehwere that “blonde” is feminine and “blond” is masculine. Is that correct?
Yes.
My wife and I are both brown haired, although blond(e) as children. Both our kids are fair-haired, and it seems like our teenage daughter is likely to stay that way. (Before anyone makes “milkman” comments, both kids look a fair bit like me - and they were conceived some 1200 miles apart). The question I would really like to raise, though, is what about the (much rarer) red haired gene? My sister-in-law is a redhead, as is my nephew. My brother was blond and went darker in adolescence, so it would seem the dominant “hair gene” in his makeup was from our mother, who did the same thing. There is no evidence (as far as anyone can tell) of red hair on our dad’s side of the family, from whom any recessive gene would have had to come. Our ancestry is, however, almost exclusively Irish (blame our lone French great-great-grandfather for the unspellable surname), so it is not inconceivable that there may have been red hair 5 or 6 generations back on that side of the family. How far can a recessive gene “throw back”? Or should my brother worry about HIS milkman?
Cecil,
Your Mendelian paired allele explanation is cute, but far from accurate enough in any setting outside of a Junior Highschool biology class. What about such concepts as overdominance, interaction, the polygenic model, etc. Your reductionism may not be entirely incorrect, but lack of a thorough treatment can certainly lead one to leap to incorrect conclusions. Poor William is probably drawing up Punnett squares as I write this, believing he can map out the traits of his offspring as if they were fruit flies.
Cheers,
Waverly
Okay, now, William is the guy who thought dominant traits might have something to do with whips and chains. I wouldn’t worry too much about his ill-conceived Punnett squares. 
about blondes: “blonde” is feminine and “blond” masculine … IN FRANCE! In english, any distinction there may have been has been forgotten, except that somehow most of us ended up using “blonde” as a noun (eg, dumb blonde) and “blond” as an adjective (eg, woman with blond hair).
As for genetics, well, you’re all right. Cecil should have gone for fruit fly eye colors, because everyone’s now trying to remember the color of their milkman’s hair. It’s a good thing nobody asked about dominant diseases, or skin color, or eye color, or anything along the lines of what Waverly said.
-beth, biology grad student who knows far more about genetics than she ever wanted to
Actually, the distinction between “blond” (noun, masculine) and “blonde” (noun, feminine) is recognized in English, as examination of any respectable dictionary will show. However, “blond” (adjective) is used of both genders, because English adjectives don’t decline.
This just reminded me of curious Dutch phrase which translates to “milkman’s dog hair” [sorry I can’t recall the original Dutch]; referring to a mottled blonde.
So those attempting to remember the milkman’s hair color, take heart. Things could be much worse.
I think the red-hair gene is (a) somewhere else in the genome, not the same place as the hair-melanin genes; & (b) pretty well masked by the dark-hair gene, as the melanin kind of obscures the red pigment. So you can have the red-hair gene & red pigmentation, but your dark hair covers it up. But someone who actually took genetics may correct me. (Of course, I know cases where two red-haired parents produced dark-haired children, so don’t assume it’s that simple.)
eye and hair color genetics here:
http://www.kumc.edu/gec/support/eyecolor.html
bottom line: red hair looks like it might be recessive, but maybe not. (if it is, you’re likely right in the mechanism - that’s how this kind of thing often works out). Same for eye colors: nobody really knows what the deal is, but it’s probably not a simple mendelian trait. There may be more than one gene at work, but the geneticists haven’t figured it out yet. And don’t even ask them about gray or purple eyes.
Here’s a simpler example of recessive pigmentation genetics: parakeets. Wild parakeets are green and yellow, caused by having both a yellow pigment and a blue pigment that mixes with the yellow in places to make green. If the yellow gene is broken, you get a blue and white bird. If the yellow gene is fine but the blue gene is broken, you get a yellow bird (lutino). If both are broken, you get a white bird (albino).
Isn’t blood type an even simpler example of dominant/recessive traits? A, B, AB, O? Or is there more to it than that (as there usually is around here)?
The problem with using blood type as an example, of course, is that you don’t have any sort of phenotype to compare.
ABO blood group is an example of both codominance and complete dominance.
A is completely dominant to O. B is completely dominant to O. O means that the gene does not code for a protein (neither A nor B).
A is codominant to B, meaning that when both are present, both are expressed, and thus AB phenotype exists.
Rh factor is simple dominant/recessive trait. Positive (+) is dominant to negative (-). A positive person can either be ++ or ±, a negative has to be – in order to express the trait (in this case, no formation of said particular protein).
Well, yeah, you can’t tell the difference by looking at the person, true. But it’s about as simple a case of dominant/recessive traits as there is, isn’t it? Or Rh, I guess, if you can’t deal with the codominance thing.
One of my mother’s eyes is part brown and part blue.
Explain that one!
My mom is a redhead, my dad has dark brown hair. All three of us kids were born blond, and as we got older:
my hair is now vaguely strawberry blonde,
my sister’s is a sandy blonde,
my brother’s is a dark blonde.
I’m so confused.