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What are the chances my baby will have red hair?
June 22, 2009 11:48 AM   Subscribe

What are the chances my baby will have red hair?

My husband is a blue-eyed redhead of Irish descent. I have brown hair and green eyes and am of mixed Eastern European descent, although I do have a grandfather from Scotland. There aren't any other redheads in his immediate family that I know of, and none in mine, either, though a couple of great-aunts on both sides of my family were redheads, as well as a couple of second cousins. Possibly my great-grandfather on one side and great-grandmother on another side.

Anyway, everyone's on my case about having a redheaded baby (because I clearly have control over that), so I'm trying to find statistical info on it. Thanks!
posted by anonymous to Science & Nature (32 answers total) 8 users marked this as a favorite
 
Assuming straight mendelian genetics, your husband is rr, and you're probably BB, putting the chances of a redheaded child at 0%. If you carry the recessive r gene, your chances rise to 50%.
posted by Oktober at 11:55 AM on June 22, 2009


Red hair and blue eyes are recessive. Let's call the red hair trait R. Each person has two copies of the gene, one inherited from the father and one from the mother. Additionally, each copy can be dominant (big R) or recessive (little r). Only in the case of both recessive will the child have red hair. This is best illustrated in a table:

RR = brunette
Rr = brunette
rr = red hair

We know your husband has two recessive copies.

What we don't know is you. You are either RR or Rr. That there are other redheads in your family means you may be Rr.

If you're RR, no matter what you won't have red-headed children.

If you're Rr, there's a 50% chance: your husband will always give a recessive copy (r), and you have a 50% chance to give a recessive copy (r).

So it's either 1/2 or zero. You'll find out soon enough! :D
posted by dualityofmind at 11:57 AM on June 22, 2009 [4 favorites]


There's no way to know whether you actually carry the gene for red hair, but it sounds like it's possible. It would be about a 25% chance if you do, since your husband obviously does.

I am a redhead with two non-redhaired children. Hopefully your husband isn't part of the everyone who's on your case, because your odds ain't hot.
posted by padraigin at 12:00 PM on June 22, 2009


FYI, the gene for red hair works funny, it's not like blue eyes or peapods. There are several articles about this on Google, pretty much all of which I read when I was trying to determine the odds of having redheads myself.
posted by padraigin at 12:02 PM on June 22, 2009 [2 favorites]


OK. Red hair is not a simple autosomal recessive trait (there are a bunch of different kinds of red hair, basically), but it acts a lot like one.

If you have a great aunt (that is the sibling of your parent's parent) who is a redhead, but neither of their parents was a redhead, your great grandparents must both have been recessive for red hair (in order to have a redheaded child). That means that your grandparent has a 1/2 chance of carrying the gene, your parent has a 1/4 chance of carrying the gene, and you have a 1/8 chance of carrying the gene.

Of course, that analysis only applies to one side of your lineage. Since you have red-headed great aunts on both sides of the family both of your parents have a 1/4 chance of carrying the gene, as do you.

So there's a 1/4 probability that you're a recessive carrier. If you were a carrier, there'd be a 50% chance that the baby has red hair. Multiply the probabilities, and you can see that there's a 1/8 chance that your baby will have red hair.

You're sure that your great aunts aren't dyeing their hair, right?

Somebody check my work, please.

It would be about a 25% chance if you do, since your husband obviously does.

50%.
posted by mr_roboto at 12:04 PM on June 22, 2009


I do not have red hair. Nor do my parents. My husband does not have red hair. Nor do or did his folks, or either of his sisters. In fact, none of us knows of any redheads on either side.

Our youngest has flaming, flaming red hair.

What we do have is positive Irish ancestry on his side, and probable Irish ancestry on mine.

So, roll the dice.
posted by St. Alia of the Bunnies at 12:07 PM on June 22, 2009 [1 favorite]


You're right, because he'd have both copies of the gene. My mistake.
posted by padraigin at 12:08 PM on June 22, 2009


Oh, and if you can confirm that you have a red-headed great grandparent on each side, that would imply that one grandparent on each side was definitely a carrier, so each of your parents would have a 50% chance of being a carrier (as would you), so the baby would have a 25% chance of being a redhead.

These are minimum probabilities, as it's possible that other individuals in your lineage were also carriers. These probabilities are constrained only by known occurrences of the trait.
posted by mr_roboto at 12:18 PM on June 22, 2009


Funny thing with red hair. Both parents need at least a recessive or dominant copy of a mutated allele on MC1R to get a child with red hair. You husband has two dominant copies, one of which he will definitely pass on to the child, and you MAY possess it. If you do then it'd be 50%. If you don't, then no luck. I don't know how to calculate the odds of you having it.

That said, it does tend to crop up. Neither of my parents or their families had red hair, or freckles (two more mutated alleles on MC1R) for that matter. I ended up with both. Completely flummoxed a lot of people till my mom remembered a Kelly surname in the family. I just found out my dad's side is descended from Ireland as well. It was all so long ago that most everyone thought it was Norway (long story).

So, the chances of my parents meeting and then having a red haired freckled kid is astronomically against. But here I am. There were at least six generations without a trace of red hair or freckles. Then there was a cousin and I, in the same generation. They say it's a recessive gene but that doesn't prevent it from hanging on anyway.

Anyway, I like to use that story to remind people that we're all mutants, not just X-Men, and the child will therefore be absolutely unique in their own special way. There's something like 26,000 genes and we've talked about exactly one here. Think of all the possibilities.
posted by jwells at 12:21 PM on June 22, 2009 [2 favorites]


That means that your grandparent has a 1/2 chance of carrying the gene, your parent has a 1/4 chance of carrying the gene, and you have a 1/8 chance of carrying the gene.

Of course, that analysis only applies to one side of your lineage. Since you have red-headed great aunts on both sides of the family both of your parents have a 1/4 chance of carrying the gene,


So far, so good.

as do you.

Not quite. Each parent is 3/4 likely to have the BB genotype and 1/4 likely to have Br genotype. Which means, overall, each parent is 7/8 likely to pass on a B allele and 1/8 likely to pass on an r allele. Which would mean a 49/64 chance of anon being BB, 14/64 of being Br, and 1/64 being rr. Except we know that anon is not red-headed, so we can eliminate the rr possibility, leaving a 14/63 (=2/9) chance that anon is Br, and a 1/9 chance that a child will be red-headed. Small difference though (11.1% instead of 12%), and probably outweighed by hair color not quite being a classical Mendelian trait, the possibility of unconsidered r alleles from other ancestors beyond those known to be redheads or related to redheads (what's the overall incidence of r in the relevant ethnic populations?), etc.

Also note:

Possibly my great-grandfather on one side and great-grandmother on another side.

If this were the case, it would increase the chance of the corresponding parent of anon's of having the Br genotype from 1/4 to 1/2. If one great-grandparent is red-headed, the probability of anon's child being red-headed rises to 5/31 (16.1%); if both are, the probability becomes 3/15 (=1/5, 20%).
posted by DevilsAdvocate at 12:25 PM on June 22, 2009


(11.1% instead of 12%)

Sorry, that was supposed to be "(11.1% instead of 12.5%)".
posted by DevilsAdvocate at 12:26 PM on June 22, 2009


You husband has two dominant copies

Recessive. Red hair is recessive.
posted by mr_roboto at 12:26 PM on June 22, 2009


Not quite. Each parent is 3/4 likely to have the BB genotype and 1/4 likely to have Br genotype. Which means, overall, each parent is 7/8 likely to pass on a B allele and 1/8 likely to pass on an r allele. Which would mean a 49/64 chance of anon being BB, 14/64 of being Br, and 1/64 being rr. Except we know that anon is not red-headed, so we can eliminate the rr possibility...

I don't think you're wrong about this, but why doesn't the same analysis apply to the previous generation?
posted by mr_roboto at 12:33 PM on June 22, 2009


Thanks for introducing this discussion. My husband's a brunette with brunette parents and a red-headed brother. I'm a brunette with brunette parents. Irish ancestry on my side. We had a flaming red-headed boy that so surprised both of us it took us both a minute to shake the surprise off our faces when he was shown to us by the midwife.
posted by rumposinc at 12:46 PM on June 22, 2009


mr_roboto: "If you have a great aunt (that is the sibling of your parent's parent) who is a redhead, but neither of their parents was a redhead, your great grandparents must both have been recessive for red hair (in order to have a redheaded child). That means that your grandparent has a 1/2 chance of carrying the gene,

2/3, I think: The options were RR, Rr, rR, and rr. rr is ruled out, but rR or Rr is more likely than RR.

So your parents each had a 1/3 chance of being carriers, and you had a 1/9*1/4 chance of being a redhead, but weren't, so a 1/9*2/3 (both parents carriers) + 4/9 * 1/2 (one parent a carrier) = 8/27 chance you are, and a 4/27 chance your child is.
posted by alexei at 1:06 PM on June 22, 2009


My parents brunette and ginger-ish had 3 kids. Blonde, redhead then another blonde. You could try to predict it as much as you like... but I think you still just kinda get what you get anyway :)
posted by mu~ha~ha~ha~har at 1:20 PM on June 22, 2009


I don't think you're wrong about this, but why doesn't the same analysis apply to the previous generation?

You are correct; it would. My mistake in not considering that. Let me try again.

[To be clear, let me state simplifying assumptions up front: 1) that anon's four great-grandparents who are not related to the red-headed great aunts are BB; 2) that the "possibly" redheaded great-grandparents are the parents of the known-redheaded great aunts, one apiece; 3) that brown vs. red hair color is a classical Mendelian dominant/recessive trait. In practice, of course, (1) may be incorrect; anon could confirm (but we don't know for sure) whether (2) is correct; (3) is known to be incorrect but is not too far off. Any of these would affect the resulting probabilities.]

For anon's two grandparents, one on each side, who are brunette but siblings to redheads, they are each 2/3 likely to be Br and 1/3 likely to be BB if both of their parents are brunette. (If one is a redhead, they are guaranteed to be Br, of course.)

Thus, anon's parent's are each 1/3 or 1/2 likely to be Br (if their grandparents are all brunette or one is a redhead, respectively), and 1/6 or 1/4 likely to pass on the r gene to anon.

anon's probability of being Br are 10/35 (=2/7), 8/23, or 6/15 (=2/5) (with 0, 1, or 2 red-headed great-grandparents, respectively) and the child's probability of being redheaded is half that: 1/7 (14.3%), 4/23 (17.4%), or 1/5 (20.0%).

On preview: So your parents each had a 1/3 chance of being carriers, and you had a 1/9*1/4 chance of being a redhead, but weren't, so a 1/9*2/3 (both parents carriers) + 4/9 * 1/2 (one parent a carrier) = 8/27 chance you are, and a 4/27 chance your child is.

The "but you're not a redhead" caveat has to be applied to all possibilities, not just to the case where both parents are carriers. The information that anon is brunette makes it slightly more likely that only one parent is a carrier and slightly less likely that both parents are carriers. In other words, it should be: 1/9*1/4 (=1/36) chance of being a redhead, 1/9*2/4 [both parents carriers] + 4/9*1/2 [one parent a carrier] (=10/36) chance of being a carrier; except we know anon is not a redhead, so it's a 10/35 chance of being a carrier.
posted by DevilsAdvocate at 1:39 PM on June 22, 2009


Anyway, everyone's on my case about having a redheaded baby (because I clearly have control over that), so I'm trying to find statistical info on it.

It's possible that those folks will both win and lose. Some of us with sundry redheads in the family are born with flame-red hair that falls out in infancy, to be replaced with a different hair color (light blonde, in my case.)

As I got older, my hair got more reddish, though I wouldn't be considered "a redhead" (were it not for hair dye.) But the relatives who are really keen to see your husband's red hair in his child may be able to find a way to do so regardless.
posted by desuetude at 1:44 PM on June 22, 2009


Sorry if this is unclear: "(If one is a redhead, they are guaranteed to be Br, of course.)"

I meant "(If one of the grandparent's parents is a redhead, that grandparent is guaranteed to be Br, of course.)"
posted by DevilsAdvocate at 1:45 PM on June 22, 2009


I have nothing to contribute other than I love that you asked this question because I (South Asian with black hair, brown eyes, but a blue-eyed grandmother) am marrying a red-headed blue eyed man myself and desperately want our babies to have red hair. Alas, I think I'm out of luck on the hair, but maybe not on the eyes!!
posted by echo0720 at 1:46 PM on June 22, 2009


I can't answer for odds, but if either of you have freckles, the odds are greater. It's a bit complicated but these articles about the genetics of red hair are really interesting:

http://www.thetech.org/genetics/ask.php?id=44
http://www.thetech.org/genetics/ask.php?id=230
http://www.thetech.org/genetics/ask.php?id=189
posted by for_serious at 1:56 PM on June 22, 2009 [1 favorite]


Not a truly useful answer, more apocryphal than anything:

When I saw my brother's son (red curly hair, blue eyes, pale skin) and looked at my brother (same) and his spouse (black, straight hair, brown eyes, olive skin) I stared questioning probability since it seemed as if there was a lot going against that one (I know, I know, coloring is tied together). Then my first (reddish straight hair, blue eyes, pale skin) has me (reddish straight hair, green eyes, pale skin) and Mrs. Plinth (dark, straight hair, brown eyes, olive skin). I coined the term "dominant recessives" where I think my family's genetics work really hard to assert themselves and make everything else genetic spackle.

I know this isn't true, but dang it's pretty improbable.

Useful answer (to some):
Probability aside, until there's a reasonable, non-risky screening process and until a point when there is a good reason for designer children, you get what you get.

There's a quote from Garrison Keillor which sums this up, "Some luck lies in not getting what you thought you wanted but getting what you have, which once you have it you may be smart enough to see is what you would have wanted had you known."
posted by plinth at 2:09 PM on June 22, 2009


Red hair is most common in Ireland and Scotland, though those are certainly not the only places redheads come from. Your other ancestors besides the Scottish one could have red hair genes. Wikipedia entry on red hair, read the part on modern geographic distribution.

These things are really complicated to predict, as it's not simple Mendelian genetics, as others have said.
posted by ishotjr at 2:48 PM on June 22, 2009


yeah, what they said. seems like the redhead genetics are very....capricious.

I was (much like desuetude) born with redhead (pale strawberry) which turned blonde when my 'mature' hair grew in at 1 year old.

I am mostly Irish and there are random redheads on both sides of the family...but they are soooo unpredictable.

my dad's brother (Irish, but dark hair, eyes, and warm skintone) married an Italian decent woman (dark hair, eyes and olive skin) yet produced a son with pale skin, bright red hair and green eyes...they must have hit the single most unlikely genetic combo they could have made.

good luck! I hope you have a healthy child and I feel ya, cause if I had children I would hanker for the red myself :)
posted by supermedusa at 2:56 PM on June 22, 2009


My father's father had red hair. My father's sister had red hair. I have black hair with three flaming red hairs in my beard.
posted by mrmojoflying at 3:18 PM on June 22, 2009


I know of two sets of brunette parents who ended up with flaming redhead children, I don't think anyone HAD been a redhead for a few generations before. I suspect redheadness is a crapshoot.
posted by jenfullmoon at 3:32 PM on June 22, 2009


No one in my parent's generation has red hair (aunts and uncles, my parents themselves). Don't think any of the generation above that did, either. Out of 10 kids, 4 are redheads. YMMV.

And for what it's worth (looking at you, yellowbinder) redheads/gingers etc get made fun of a lot in school. It's not really a big deal, but apparently redhair is of the devil. Light-colored freckles, also of the devil. Darker ones, kissed by an angel!
posted by shownomercy at 5:29 PM on June 22, 2009


I had one blond parent, one brunette, but a red-haired aunt. My siblings were all either brunette or blond, but I was "blessed" with copper tresses.

... but have never ever actually encountered someone making fun of red haired folk.
"Carrot top!" "Hey, Pippi Longstocking, is your temper as bad as they say?" "Does that hair glow in the dark?" "Have you got freckles all over?" "She must be embarrassed - she's turning as red as her hair!" "Let's play connect the dots with those freckles!" "Are you a *real* readhead, snicker snicker? Why don't you prove it to us!" "Ooh, what have we here, a redhead? Insatiable in bed, I hear! Is that right?" "OMG, your temper is as bad as they say!"
Heard 'em all. Way to make a kid feel like a freak. Sigh.

posted by fish tick at 5:35 PM on June 22, 2009


I think there might be two types of red hair- the classic recessive type (cough Conan cough), and the type that's almost an offshoot of the sandy-blond variety. Much less apt to be freckly and curly and pale.
posted by gjc at 7:22 PM on June 22, 2009


I don't have statistical info for you, but I'll offer a scenario. My mom was a brunette/hazel eyes with no redheads in the extended family to speak of (but she always dyed her hair an awful shade of red - never, ever understood that). My dad had black hair, but two of his sisters had dark red hair. I got the dark red hair and his dark brown eyes, and it's gororogeous, so I totally get why they want to see a redhead from you.

Redheads are also less hirsute in general, and that totally works for me. Rowr.
posted by heyho at 10:39 PM on June 22, 2009


Genetics are funny sometimes, echo0720. My sister is 1/2 Korean, with a red headed father. She has dark brown eyes, curly brown hair with reddish highlights, and freckles.
posted by gudrun at 10:50 PM on June 22, 2009


Assuming straight mendelian genetics

This is where this thread went wrong. "Variation at MC1R is apparently neither necessary nor sufficient for red hair colour..." (Spritz 1995). MC1R itself has at least 65 alleles. Variants here seem to be responsible for most cases of red hair but there are a significant number of cases of redheads with only one or even zero MC1R variants. There's a lot we don't know about red hair genetics, so I would caution against doing the sort of arithmetic seen elsewhere in this thread.
posted by grouse at 10:56 PM on June 22, 2009 [1 favorite]


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