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This question may be answered more easily by people who know about genetics. I'm pretty sure that hair type is controlled by genetics, and I heard somewhere that genes that give curly hair are "dominant" over genes that give straight hair. What I find interesting is that there seem to be more straight-haired guys on this board than curly haired ones. I was wondering if what I heard (curly haired genes dominant) is just so much hogwash or if there are other reasons for the dominance of straight hairs here. Maybe the actual reason is that since curly hair is so much harder to grow long, more curly haired guys tend to give up because of a difficult awkward phase, etc.
David
Here is a response I wrote about MPB & genetics. It would apply to curly/straight also, as will the link following:
Genetics plays a major role, but it is a complicated one. If MPB is a recessive trait, and your father has both genes for MPB, and your mother has neither, you will have a 25% chance for MPB. If it is the dominant trait, you would have a 75% chance for the same. If both parents carry the MPB genes as a pair, you have a almost 100% chance of MPB, and if both parents do not have the MPB genes you stand a good chance of having hair throughout your time here.
However, hair genetics is more involved. It is called polygenic traits, meaning more than one pair of genes has an influence. Therefore a combination of many minor influences can impact the dominant or recessive traits as expressed, and change their appearance. If anyone is interested, here is a link to a basic explanation of genetic principals:
http://biology.about.com/gi/dynamic/offsite.htm?zi=1/XJ&sdn=biology&cdn=education&tm=4&f=00&su=p284.2.420.ip_&tt=2&bt=0&bts=0&zu=http%3A//anthro.palomar.edu/mendel/default.htm
Hope this helps.
George
Thanks for the insight. I guess my main question was why, if curly hair genes supposedly are dominant, there seem to be more straight haired guys here. I wonder if what I heard about curly hair being dominant is actually wrong, and if anyone knows what the dominant hair type gene is. (As eye colour is determined, brown dominant over blue)
David
According to the following article, curly is dominant and straight is recessive. I have copied the text:
Ask a Geneticist
by Dr. Barry Starr, Stanford University
Can a couple (one with straight hair, one with curly) have one straight haired child and one curly haired, and one of the children has green eyes and the other blue? Both parents have green. Is this possible?
The quick answer is that it is possible for the couple you describe to have kids with blue or green eyes. (Although less likely, it is even possible to have a brown-eyed child.)
In terms of hair type, by the traditional sorts of theories that are out there, it isn’t possible for a curly headed and a straight haired couple to have straight haired kids (or, by a strict definition, curly haired kids either!). Of course, genetics is always more complex than the traditional sorts of theories.
One way for the couple you describe to have a straight haired child is if the curly headed parent actually has wavy instead of curly hair. It may seem like a minor distinction but from a genetic point of view, the difference is critical.
Why would this distinction matter? Remember, that for most genes, you have two copies of each gene that you inherited from your mother and your father. For most “traditional” genes, there is a dominant and a recessive version. What this means is that if you have either one or two copies of a dominant version of a gene, you’ll look like that gene. To look like the recessive version, you need two copies of the recessive form.
For example, with something simple like whether earlobes are attached or not, there are two versions (or alleles) of the ear lobe attachment gene. Free earlobe (G) is dominant over attached (g). What this means is that if you inherit a G version of this gene from either your mother or father, you will have free earlobes. To have attached earlobes, you need to get a g copy from both parents.
So, from a gene point of view (or genotype), both a GG and a Gg person has free earlobes and a gg has attached earlobes. So how does it work for hair type and eye color?
Neither hair type nor eye color works in this simple way. There are two versions of the hair type gene, curly (C) and straight (s). Hair type is an interesting case of something called incomplete dominance. What this means is that with hair type, if you have one of each version of the gene, you get a mix of the two or wavy hair. So for hair type, CC gives curly, Cs gives wavy and ss gives straight hair.
Back to your specific situation. As you can probably tell, the couple you describe could only have wavy haired kids. That is because the curly headed parents, CC, can only contribute a C gene and the straight haired parent, only an s gene. That means all the kids will be Cs and have wavy hair.
Of course, wavy and curly is in the eye of the beholder! If your curly headed person actually had wavy hair, he or she would be a Cs. A wavy haired person can contribute either a C or an s gene. If paired to a straight haired person (ss), then the kids would either have straight (ss) or wavy hair (Cs).
That is probably way more than you wanted to know! For eye color, I’ll refer you to two questions we’ve answered previously. The first is a description of traditional eye color inheritance that will work well for your case. The second is a nice description about hoe the genetics rules are sometimes broken.
Hi Big George,
Thanks for the scientific explanation--it confirms what I thought about curly being dominant and the resulting hair type being determined much like eye colour. Reminds me of my high school biology--a LONG time ago. I was wondering if you are a scientist--you seem very knowledgable in this. I am a scientist, but a chemist rather than a biologist so my knowledge of genetics is what I remember form 35-40 years ago. (I still find it puzzling why there are so many straight haired guys here--maybe it IS because straight hair is easier to grow and many curly haired guys give up growing their hair do to a worse awkward phase. I still wish I was blessed with straight hair myself)
Thanks,
David
I was wondering if you are a scientist--you seem very knowledgable in this.
Actually I am a microbiologist by schooling; had planned to go California and get an advanced degree in Marine Microbiology until I discovered what the job market was like; I could bag groceries with a B.S. just as easily as with a Ph.D. So now I am a general contractor. Have always been a science and math lover; still am and find it interesting. It was quite a while ago for me also, so I have to do a bit of research to see if my memories are still correct.
And many of us straight hair guys would love to have some wave to our hair; just another example of the grass always being greener . . . . .
George
The genes concerning MPB are DOMINANT, which means that the gene may express itself wheather it comes from the mother, or the father. This is why that MPB may be inherited from the mother, or the father. Only one parent is required to have the gene. However, for MPB to occure the individual must be genetically susceptible to MPB.
my dads hair is thin and dead straight and my mums is thick and wavy/curly
my 3 sisters have dads and i have mums....that sure fits with a punnet square theory
i reckon the different types are different dominances/co-dominances as you can get different degrees of curlyness