What are my chances of producing a red haired child? (and other questions)

Factual Questions
1

Since these are gene questions, I know there are no absolute answers, so I’m only asking for an educated guess to each.

First question:

I have red hair, as does my brother, and our mother. The assumption of why he and I both inherited mom’s hair color instead of dad’s brown is that Dad is 1/3rd Scottish, which seemed to have mixed well with mom’s Irish half…(he also has a lot more red haired family members then she does, since her grandmother is the only other on her side of the family). Does the fact that we both inherited mom’s coloring make us(and our future spouses) more likely to have red haired babies than the average person? Would our spouses’ nationalities affect this much?

Second question:

Had my mother and father had more children (let’s say two more) would the fact that both of their existing children were born with red hair make these hypothetical children more or less likely to also have red hair?

Third question:

My brother is nearly ninteen and worried that his hair is getting darker (I think that he’s merely comparing it to my hair which is bleached by the sun, while his isn’t). Is it possible that it will change to brown on him now that he’s an adult? If so, how old would he have to be before his only worry will be if it turns gray?

2

No, the chances are exactly the same every time.

3

Well, here’s a crude understanding of red-headed genetics from a fellow redhead:

Red hair is a recessive gene compared to most other hair colors (possibly all other hair colors – I’m not sure). If you have red hair, it means that your hair gene is pure red: you’ll definitely pass on a red gene to any kid you have.

Your partner can have three relevant hair-gene types:

  1. He (I think you’re a woman; please forgive me if I’m wrong) could be redheaded. In this case, barring mutation, your kids will definitely have red hair: both of you have pure red hair genes, and both will definitely pass on a red hair gene to your kid.
  2. He could be (for example) a brunette with a recessive red hair gene. In this case, he stands an equal chance of passing on the brown hair gene or the red hair gene to the kid. Since the brown hair gene is dominant, if he passes that one on, your kid will have brown hair. If he passes on the red hair gene, your kid will have red hair.
  3. He could be a brunette without a recessive red hair gene. In this case, since whichever gene he passes along will be dominant over the red hair gene you pass along, your kid will not have red hair.

So, depending on the redhead’s partner, the kids will either be 100% redheads, 50% redheads, or 0% redheads.

It’s a little more complicated than that, I think: I believe there’s a whole set of genes that determine hair color, not just one, and I think that throws off the odds a bit. But the basic idea should be solid. If you want redhead kids, marry a redhead.

Daniel

4

Dan’s pretty much right. If I remember my Punnit Squares from biology, let’s say the red hair gene is rr. Even though it’s a recessive gene, if you mate with redhead your Punnit will look like a tick tac toe grid with only four squares, the gene rr in all 4, so your chances of having a redhead are 4 out of 4.

If you mate with someone with another hair color, they might still be carrying a redhead gene as a recessive trait. So if say, black hair is RR, they might really be Rr (dominant black, recessive red) if that were the case, your Punnit square would have Rr in the top left quadrant, Rr in the top right, rr in the bottom left and rr in the bottom left, so your odds in getting a red headed child are 2 out of four.

If the person is carrying no redheaded chromosome (RR) then your Punnit square would be Rr in the top left, Rr in the top right, Rr in the bottom left, and Rr in the bottom right. So the odds are you’ll have a black-haired child every time. Redhead chances are 0 out of 4.

(Sorry I couldn’t figure out how to make the squares…and sorry if I spelled Punnitt wrong, it’s been quite a while.)

5

What I remember is that red hair is a special case, or subset, of blonde hair. The red hair gene will not be expressed (other than possibly red highlights) unless one first has the blonde genotype.

So first, we have B=brown hair/dominant and b=blonde/recessive. Then we have R=not red/dominant and r=red/recessive. Then:
B?=brown hair
bbR?=blonde
bbrr=red

So you, mom, and bro are bbrr. Dad is Bb?r. If Dad is BbRr, the odds for your future siblings are 50% brown, 25% blonde, 25%red. If Dad is Bbrr, those odds are 50% brown, 50% red.

So, question one, yes, you’re more likely than the average to have red-haired offspring. Spouse’s nationality has nothing to do with it, spouse’s genotype has everything to do with it. (Okay, I know by nationality you mean ethnic heritage, and yes, that relates to some degree to genotype–you don’t see much natural blonde hair in China, for example.) If spouse has BB genotype, all kids should be brown-haired. If spouse has bbrr genotype (red hair herself), all kids should have red hair.

Question two, your red hair doesn’t affect the likelihood in question, but it demonstrates the presence of b and r genes, which make it more likely than average (compared to the population as a whole).

Question three, yes, it may darken. Many folks’ hair darkens with age. My nephew had almost white blonde hair as a kid, at 30 his was dark blonde, on the edge of light brown. My dad was nicknamed “Red,” but by middle age had essentially medium brown hair. As far as when hair may turn gray, that varies all over the map (though it seems to be an inherited trait, i.e. runs in families as early or late). I suspect it’s the same for when light hair colors may darken.

6

Most interesting, Gary T, about the red/blonde relationship. My mother, who had 4 (of 6) redheads, with a dark-haired husband and brown hair herself, keeps telling me that she heard somewhere that you had to have “a pure blonde gene” in order to have red hair. Of the two kids in our family who are not redhaired, one is blonde (the other is a brunette).

As to darkening of hair, my mom’s mom, who was a redhead as a child, went dark around the age of twelve and by the time my mom knew her, was a brunette completely. I worried about my hair going dark, too, in my early teens, having heard my grandma’s story, but all four of us are flamingly red so far. :slight_smile: Apparently we’ve inherited from our paternal great-grandfather, who was said to have been redheaded until he went grey.

I’ve heard that redheads go white (as opposed to grey) when they get older. Anyone know if that’s true?

7

GaryT, that is interesting. I’m another redhead child of two brownhaired parents – and 2/3 of us kids are redheads. THe next closest redhead relative we have is a great-uncle, and I don’t know of any blondes on either side of the family.

Genetics are funny, eh?
Daniel

8

Nenya, everyone goes white, as opposed to grey. When you have white hairs showing up amongst dark ones, though, the net effect is grey.

If red hair requires a blond genotype, then that would imply, would it not, that a dark-haired person cannot have parents who are redheaded and blond, respectively, right?

9

Yes. Now, I don’t claim that what I posted is the complete story–there may be other gene pairs involved in hair color. But it’s what I remember from a biology class years ago, and it seems to be largely true from casual observation.

Red hair is known to often skip a generation. If a BBRR mated with a bbrr, all of the kids would be BbRr, brown-haired. But if that BbRr mated with another BbRr, blondes and redheads would be possible.

It’s also possible to have, through fate, any number of individuals and/or generations with Bb, and thus no blondes, but the potential for a blonde (and maybe a redhead, depending on R/r genes) to pop up at any time.