View Full Version : Genetic question about hair structure

natt i nord
December 21st, 2010, 09:25 AM
I just wondered - if a couple got a child, in which the mother has, let's say very straight 1a hair and the father very curly 3c or even 4a hair - which where the possibilities the child's hair could turn out? Only 1a or 3c/4a or everything in between, too? :hmm:

TIA :)

December 21st, 2010, 09:49 AM
I think the full range is possible, but it seems like curly hair often predominates in mixed-race folks where one parent had 4ish hair.

December 21st, 2010, 09:53 AM
Well both my parents have straight hair and my DS and I have curly which I assume came from several curly haired grandparents so you dont follow just one of your parents traits, its a mix :)

December 21st, 2010, 09:57 AM
I think the full range is possible, but it seems like curly hair often predominates in mixed-race folks where one parent had 4ish hair.

I agree with Anje here, my mother has curly thick hair and my father has straight thinner hair. and i ended up with a mix little less than medium thickness, with wavy hair that can also be straight by just combing it when its wet. but always has that curl at the end, not too hard to manage if i let it go wavy. but a pain to manage if i wanna keep it straight, so i just let it go wavy most of the time.

December 21st, 2010, 10:07 AM
I think genetic traits like this can be such a surprise bag, if I remember from biology hair curliness, like skin color is a multiple allele trait. Meaning that the trait - texture of the hair - is made up of several genes, it isn't something that is either / or.
That said , both of my parents have extremely curly hair and mine is at best wavy , especially underneath.
So who knows ?
In a tangent my son has blond hair and my husband and I both have very dark hair mine soft black and his very dark auburn, you just never know what the kid will get.

December 21st, 2010, 10:42 AM
Firstly, lets roughly summarize the traits in question. Curly hair 3a+ tends to be a dominant trait when paired with a hairtype straighter than itself. Plus, you also have the curly parent's ancestry to consider because he can have the genetic coding for both traits in his DNA, even though he only exhibits one trait. You have to ask what sort of hair did his parents and grand parents have?

This is important because recessive genes like very striaght hair can be hidden by more dominant genes like curly or wavy hair, but pop up in a later generation if paired with a gene like it. It depends on whether the curly haired parent is a homozygous or heterozygous curly haired person.

If he is homozygous, which means he has inherited genes for curly hair from both his parents, and absolutely no straight hair genes at all, his child's hair could turn out somewhere between the two hairtypes, likely on the curlier side of the hair spectrum. Possibly not as curly because of the mother, but it will usually have some curl to it, maybe anywhere from 2c to 3b/3c, but this is just a guess. The child could even get hair just like the father's with minor differences.

If the curly parent is heterozygous and carries genes for straight hair that were not expressed in his phenotype because of the presence of more dominant genes in his genotype, (in other words, if the curly haired parent has a straight haired ancestor or parent like his wife, he could have inherited genes for straight hair that were not expressed in his appearence because of the dominant curly hair genes he recieved from his curly parent or ancestor, and he passes those same straight hair genes onto his children, who's mother has straight hair, the children could end up with straight or straightish hair. The same may go for if he has wavy hair in his familial background, and the child could end up with type 1b to type 2 hair.

This is by no means a definite explaination as to what might happen, this is just a guess on my part based on what I have learned. There are still other factors I have not mentioned such as gene loci, the varying degrees of hair thickness, and even the changes in texture hair can undergo through a person's life. Genes are very unpredictable and you just never what you you're going to get :shrug:

If you're confused you could also try using a punnett square for visual aid.

natt i nord
December 21st, 2010, 10:47 AM
Ah, I forgot to add that we consider both parents as homozygous. :) But thank you for your answers, especially rena :)

December 21st, 2010, 10:58 AM
You're very much welcome :)

December 21st, 2010, 11:26 AM
Oh, I love questions like this. We should have a "science of hair" subsection. (I'm a bit of a Science geek, undergrad in genetics, currently working on my PhD in microbiology)

Rena knows much more about the genetics of hair than I do, so I have nothing useful to add, but thanks for the answer!

December 21st, 2010, 11:31 AM
My daughters father has very wiry, curly hair and I have poker straight hair. My daughters hair is poker straight like me.

December 21st, 2010, 12:46 PM
I have 2c/3a hair and my ex has 4a hair.
My daughter is a 3c.

December 21st, 2010, 01:05 PM
Wow, we have some science people here! DH teaches Biology...for a second I thought I had wandered into his class during the Genetics unit. BTW - I love doing punnet squares.

December 21st, 2010, 01:29 PM
Using Rena's Punnett Square idea:

Curly hair is usually a dominant gene.
So IF the curly-haired partner has two curly-haired genes, the child will definitely inherit one - making it a curly!
IF the curly-haired partner has one dominant curly gene and a recessive straight gene, the child will have a 50% chance of getting that gene.
However, there is more than one gene that determines our hair type, so the child could get a bit of curly and a bit of straight - making it somewhere in between.

Hope that helps!

December 21st, 2010, 01:43 PM
You could get anything!

Genetics in general are random. I mean I look like my dad, my sister looks like my mom, and my brother is a mix of the two.

And I've seen people where the kids don't look like either parent!

You could get anything!

I have curly M/ii hair and my DBF has like 1a/C/iii... if we have kids I'm praying they get his!

I have noticed though, the darker person has stronger genes. I'm white and my DBF is Mexican so I'm thinking they would have his traits over mine.

I agree with Anje, the curly could be the stronger trait if it is due to African American genes.

December 21st, 2010, 03:08 PM
I'd say curly/wavy generally is dominant over straight, but like others have said before, its very variable. In my family, my dad has straight hair, and my mom 2c (I think, but she straightens it all the time so I'm not sure). My sisters and I run the gamut - I have 2b iii hair, S 2c/3a ii and H 1a i/ii. What makes it all the more interesting is considering the genetics of cousins and aunts and uncles - there is a general trend to wavy/curly, but there's still a good amount of straight going around. Oddly enough, most of the guys have straight hair, so I'd be interested in seeing a genogram.

However, hair type is a really complex question because the phenotype starts with three parameters, and they pretty much all have multiple genes, with co-dominance, and that makes it very difficult to see a clear phenotype, i.e. you get more of a Gaussian distribution from 1a to 3c than a clearly defined difference like the Mendelian peas, where even when you had co-dominance (e.g. flower colour) there were only 3 options.

December 21st, 2010, 03:56 PM
I have type 3a hair and my sister is 3b, our other sister has maybe 1b? My Dad's hair is wavy (probably a 2c or so), my Mom's is around a 1b. My husband has wavy hair also (maybe 2b or 2c, but it's never been long so I'm not completely sure). Our son has a very strong 3b pattern.

So overall definitely a genetics crapshoot, no idea what will come out the other end! My sisters and I somehow ended up more curly than either parent, and my son is curlier than either of his parents!

December 21st, 2010, 07:12 PM

Hair curliness is a complex genetic trait ie. it is determined by more than one gene. So its not as simple as looking at both parents hair curliness and averaging that to predict the curliness of the child.

Dr. Nick Martin, from the Queensland Institute of Medical Research has been collecting twin studies data for the last 20 years. He has used this data to try and identify genes which affect things like height, or hair curliness.

So far, identifying genes which affect these traits has been very difficult. I think for height, they found 30 genes, but that only made up 4% of the variation. Because each gene that contributes to these traits has only a very small effect, it makes them hard to find (for science nerds, he is using GWAS).

To answer your actual question, the genetics of hair curliness is very complicated. There are multiple genes which contribute to it, making it impossible to predict from something like a punnet square. It'll just be a nice surprise when you have children :)

December 21st, 2010, 07:22 PM
That's about as easy as predicting the hair color ;)
Don't forget, the hair is dictated by the folical and hair changes as you grow/mature.

Such as my mom had pin straight hair/dad had natural waves/curls. My brother had thick wavy hair his whole life--I , however, had very straight hair until I hit 15, and then the waves came and now it will be spiral curls in some parts of my hair, wavy in others and then one straight pannel at the back.

Same with color for me--I was born with black hair then it fell out and went strawberry blond, and now I have dark auburn hair (somewhat enhanced to hide gray ;) )

December 21st, 2010, 08:09 PM
To answer your actual question, the genetics of hair curliness is very complicated. There are multiple genes which contribute to it, making it impossible to predict from something like a punnet square. It'll just be a nice surprise when you have children :)

If you knew the genes and dominance patterns you could possibly do a multiple gene Punnet square but those are huge and time consuming, and besides finding out your child has a 1/64 chance of getting X combination of genes (for three genes) would be pretty much the same as it being a surprise, especially when it comes to the middle where most things would be heterozygous. And this isn't even considering linkage which is possible (I've not studied hair genes in any detail, but many immune system related genes are linked, for example MHC and its transporters).

December 22nd, 2010, 02:21 AM
If you knew the genes and dominance patterns you could possibly do a multiple gene Punnet square

That was my point - these genes aren't known, because at the moment our methods are not sensitive enough to detect the effects they are having and thus identify the genes.

Hair type is also a continuous trait, so punnet squares are useless anyway. The genes don't have a dominant/recessive effect, they just change the trait along a continuos spectrum of curliness.

Hopefully my answer is clear :)

December 22nd, 2010, 05:22 AM
I have 2c/3a/3b hair and My Mother 3b/3c and my father 1b/2a. My Mother's Mother had straight hair (Indian Caribbean) and My Mother's Father had Curly Hair (Scottish/Caribbean). My Father's Mother has Straight/wavy hair (English/Irish) and my Father's Father Straight/Wavy (Irish).

So I'm just a jumbled mix in all aspects. (Pale/Tanned skin, Curly hair etc.) :D