Curly hair gene, straight hair gene

[PainterGuy]

Hi,

One of my cousins had a baby almost six months ago. The baby's father has straight hair and mother has very curly hair. After almost six months, the baby's hair started looking somewhat wavy. By "wavy" I mean a little curly. Out of curiosity, I wanted to see which gene is dominant - curly hair gene or straight hair gene. It came out that curly hair gene is dominant and straight hair gene is recessive.

I read an explanation that curly hair gene is dominant and the reason could be that humans evolved in African continent and curly hair kept the head cooler compared to straight hair. Personally, I don't like this explanation. This is how I think. There are many times that when mutations occur, they bring out noticeable changes. In the past, when proper medicines were not available and survival conditions were harsh, only people with better immune system and more competitive physical bodies had a chance to reach the age of marriage and pass on their genes. In my humble view, this was a part of natural selection. But, I'd say, there are instances, when the fertilization of an egg happens, it just happens that one gene is more assertive or dominant as a result of its chemical composition compared to the other gene which has a different chemical composition. Therefore, in such cases, there is no need for any external selective pressure or natural selection. One gene is going win, the other going to lose, or they could produce a mix of two. I'd say wave hair is a mix of straight and very curly hair. Another example would be of a person born in a harsh cold climate who has a good immune system but his body is such that it cannot handle the cold well and the reason could be that his body doesn't make much fat tissue deposits under his skin. Such a person or his offspring has less chance of survival in such harsh cold environment in the long run. This is also an example selective pressure or natural selection.

Do you think my understanding is okay as a layman? Thanks for the help, in advance!

Helpful links:
1: https://www.healthline.com/health/is-curly-hair-dominant-or-recessive
2: https://daily.jstor.org/why-do-some-people-have-curly-hair-and-others-straight/

 

[John Robertb]

Kinky hair is better in hot climates because it stays up on top of the head more and shields the brain/head from the sun AND keeps the neck and shoulder area free to perspire and help cool the all important brain. Long straight hair, in contrast, shields the neck from the cold and helps keep the head warmer in cool climates. Cross sectional samples of Asian's hair shows a better ability to insulate. Lastly, one must consider esthetics and standards of beauty which may accentuate selection for certain physical traits.

 

[Mike S.]

Be sure to distinguish between the fitness of one form of a gene (called an allele) and its dominance. Dominant alleles can be less common than recessive alleles, or may even cause lethal genetic disease and arise only via fresh mutations. It's true that run-of-the-mill mutations that basically "knock out" a gene are typically recessive, because the other copy compensates, but you can't count on that.

I didn't look deep into the genetics of straight, curly, wavy, and kinky hair, but straight hair is a simple round cross-section. It stands to reason that an allele that can make hair more of an oval shape will tend to do so whether it is present in one dose or two. So this is probably a matter of how straight and curly hair works, and certainly not a reflection of which was more successful at some earlier moment in evolution.

 

[PainterGuy]

So this is probably a matter of how straight and curly hair works, and certainly not a reflection of which was more successful at some earlier moment in evolution.

Thank you. I think you answer my question if I understand what you said correctly. My point was that not all of evolution is a result of natural selection or selective pressure. Sometimes, just one gene was more dominant over the other in terms of chemical composition therefore it affected the end result more in its favor.

 

[BillTre]

My point was that not all of evolution is a result of natural selection or selective pressure. Sometimes, just one gene was more dominant over the other in terms of chemical composition therefore it affected the end result more in its favor.

Your point that "not all of evolution is a result of natural selection or selective pressure" is correct in that, in small populations, genetic drift can also determine how a population evolves.
Whether an allele or "gene" is dominant or not is a different issue, how inherited traits are expressed. Selection will select among organisms based on their different expressed traits. A trait, whether dominant or recessive, will be selected based upon how adaptive the expressed trait is.

It seems unlikely to me that there is only one gene affecting curly vs. straight hair.
This seems like a great simplification to me.

 

[sysprog]

This 'free access' article goes into some detail $-$

The biology and genetics of curly hair
Gillian E. Westgate, Rebecca S. Ginger, Martin R. Green
First published: 31 March 2017

https://doi.org/10.1111/exd.13347

https://onlinelibrary.wiley.com/doi/full/10.1111/exd.13347

 

[LT Judd]

I could stand corrected, but I believe It has been shown clearly that the gene for blue eyes is recceisve . That is both parents have to carry the gene ( they don't both have to actually have blue eyes themselves) , for their child to have blue eyes. If one parent doesn't carry the gene, their is no way the child can have blue eyes, but he/she can still carry the gene on to the next generation.
Not sure about green , grey, light brown and all the other variations however.

 

[BillTre]

The genetics of eye color is in reality much more complex than is commonly portrayed.
Many genes can affect eye color and their interactions can add to the complexity.

from: https://medlineplus.gov/genetics/understanding/traits/eyecolor/

Eye color is determined by variations in a person’s genes. Most of the genes associated with eye color are involved in the production, transport, or storage of a pigment called melanin. Eye color is directly related to the amount and quality of melanin in the front layers of the iris. People with brown eyes have a large amount of melanin in the iris, while people with blue eyes have much less of this pigment.

A particular region on chromosome 15 plays a major role in eye color. Within this region, there are two genes located very close together: OCA2 and HERC2. The protein produced from the OCA2 gene, known as the P protein, is involved in the maturation of melanosomes, which are cellular structures that produce and store melanin. The P protein therefore plays a crucial role in the amount and quality of melanin that is present in the iris. Several common variations (polymorphisms) in the OCA2 gene reduce the amount of functional P protein that is produced. Less P protein means that less melanin is present in the iris, leading to blue eyes instead of brown in people with a polymorphism in this gene.

A region of the nearby HERC2 gene known as intron 86 contains a segment of DNA that controls the activity (expression) of the OCA2 gene, turning it on or off as needed. At least one polymorphism in this area of the HERC2 gene has been shown to reduce the expression of OCA2, which leads to less melanin in the iris and lighter-colored eyes.

Several other genes play smaller roles in determining eye color. Some of these genes are also involved in skin and hair coloring. Genes with reported roles in eye color include ASIP, IRF4, SLC24A4, SLC24A5, SLC45A2, TPCN2, TYR, and TYRP1. The effects of these genes likely combine with those of OCA2 and HERC2 to produce a continuum of eye colors in different people.

Researchers used to think that eye color was determined by a single gene and followed a simple inheritance pattern in which brown eyes were dominant to blue eyes. Under this model, it was believed that parents who both had blue eyes could not have a child with brown eyes. However, later studies showed that this model was too simplistic. Although it is uncommon, parents with blue eyes can have children with brown eyes. The inheritance of eye color is more complex than originally suspected because multiple genes are involved. While a child’s eye color can often be predicted by the eye colors of his or her parents and other relatives, genetic variations sometimes produce unexpected results.