pigmentation(some questions)

[darksphere]

buddyrydell said:

How exactly is hair color inherited?

I'm afraid I have no exact information about that. And it aint because I haven't been looking for it.

So it's not easy to find.

I have send you a chart that explains eyecolour inheritance. Hair colour is inheritance following the same basic system as that so that will show you the basics.

But it's not exact at all. I too would appreciate it if anyone has exact information on haircolour inheritance.

[jhs2006ihy]

What is the chance that a baby will be born with brown eyes?

[Batesy]

Depends on the parents. If both parents are heterozygous, then there is a 75%. If one parent is homozygous recessive and another is heterozygous, the chances are 50%. It really depends.

As for pigmentation, it's really messed up in my family. My dad has the lightest blue eyes you have ever seen, but he has very dark hair and skin (some people mistake him for Hawaiian [before they see the blue eyes of course)]. My mom is just the opposite. She has very light hair and skin and has brown eyes. As for me, I was born with light-blond hair and light-blue eyes. My skin was very pale. Now, my hair has darkened to a light brown and my eyes are more blue-gray than blue. As for my skin, it is medium-toned and is able to tan.

The fact is, all these traits (skin, hair, eyes, etc) are independent. That's why you can see black people with blue eyes or dark-skinned people with fair hair.

[Melnorme]

Batesy said:

The fact is, all these traits (skin, hair, eyes, etc) are independent. That's why you can see black people with blue eyes or dark-skinned people with fair hair.

Well, I wouldn't say they aren't exactly 'independent'. These traits have evolved together and are probably related to each other. For example, in Europe, people with different shades of blonde hair tend to have correspondingly different eye colors. ( Golden blonde - blue eyes, ash blonde - grey eyes )

[Batesy]

The only reason those traits have stayed together is because of little intermixing with other groups. However, if you take someone with brown eyes and breed them with someone of blue eyes, you will usually see some blue-eyed children and some brown-eyed children.

[Vitor]

However, if you take someone with brown eyes and breed them with someone of blue eyes, you will usually see some blue-eyed children and some brown-eyed children

that is because, some of brown eyes people have both genes...


We can be:
genes from father / from mother
A / A
A / a
a / A
and
a / a, only aa will get blue eyes

of course this is usually more complex...there are a lot of different brown/blue eyes...but it is nevertheless realistic!

Let call A for the brown gene and a for the blue gene...

Hardy-Weinberg equations:

The Hardy-Weinberg equation states that for a single gene trait with two
alleles, A and a, with allele frequencies of p(A) and q(a) where p + q = 1,
the frequencies of the three possible genotypes are given by the equation
p² (AA) + 2pq (Aa) + q² (aa) = 1


If there are 39% of blue eyes genes in a given population, you will only get 15% of blue eyes people!

interesting...
q=0.39
q^2=0.15

[Vitor]

based on this equation, if we have 25% of blue genes in a given population
you will only get:

6.25% of blue eyes in that population...
hum...
very interesting!

.25*.25=0.0625

[One Humanity]

Batesy said:

Depends on the parents. If both parents are heterozygous, then there is a 75%. If one parent is homozygous recessive and another is heterozygous, the chances are 50%. It really depends.

That sounds plausible.

My father's eyes are a mix of green, grey and brown, distributed on both eyes. It differs from picture to picture though.
My mother has chestnut-brown eyes. The eyes of her brother and my grandfather/their father, turned grey with age. The pigmentation of her brother's hair is strange too. Half of his life, it was blond, then it turned into light brown and now it's dark grey.

Here's something a skadi-user wrote about it:

It is called "infantile blondism" or incomplete blondism. It is said that 50% of Anglo-Saxon childern have this trait. I had it. My hair turned from blond to brown at about 19 years. My eyebrows and beard remained blond. My youngest daughter's hair likewise turned darker as she got into her 20s. My son's hair, however, remains blond at 25. His beard is redish. My older daughter had redish hair and it remained as such.

It was said years ago that infantile blondism was incomplete blondism whereby an allele (or more--hair being polygenetic) was inherited for dark hair and one for blond hair. This is an oversimplification.

I have dark chestnut eyes, that can look either dark, reddish or hazel. My half-brother has blue-grey eyes, due his blue eyed mother.

My father had dull medium brown hairs, my mother shiny-dark auburn/chestnut. A known of mine, who has dark brown hairs, blamed my hairs once to have blond in it (he always comments things so they sound like a blame ). But I think my hairs just have a special metallic shininess, typical for proto/pseudo-mongolid alpind-hair. The best term for it would be dark chestnut.

I didn't have blond hairs when I was born, albeit most of my kin had. But again, it had undergone a strange process: At my birth it was wavy-thin reddish-brown hair; it immediately turned flat; then a picture exists where half of my head looks platinum blond. Others taken in the outdoor look like brownish red hair, untill it soon became dark brown with a blond shine, whereas the shine today is rather reddish.

[Vitor]

I also had blond hair and blue eyes, when I was a child...

melanine sometimes takes time to develop...

[Graeme]

I don't know why all the interest in pigmentation? My children are still young, but they are redhaired and blue eyed. I don't like redhair, it is rather ugly and comes with freckles. Apparently my grandfather was redhaired, but I never knew him and can't remember him. Living in Malta he probably got melanoma. My father's eyes are blue/green, more blue than green. I always associate green eyes with reptiles and sharks. My eyes look very dark, but they are mixed though you can't see that unless you were uncomfortable close. That is a point. From my observations, a lot of blue eyed people have brown or yellow splodges in their iris and that their are a lot of mixed eyes colours like blue, green and brown though the overall effect may be blue or green or brown. My childrens' eyes are dark blue around the edges and get lighter towards the pupil with the striations being dark blue. So all that fuss about eye colour when the actual colour can't be seen unless you are eyeballing them. Anyway few people have really beautiful eyes whatever the colour.

[darksphere]

Batesy said:

The fact is, all these traits (skin, hair, eyes, etc) are independent. That's why you can see black people with blue eyes or dark-skinned people with fair hair.

That is completely untrue. There is a thing called linkage. That two traits has linkage means that the genes for them are placed closely to each other on the chromosome.

Which in turns mean that these traits are more likely to occur together. So some skin, hair and eye-colour combinations are more likely to occur together.

In fact some hair/eye and skin colours has linkage to certain blood-types and other stuff.

So these traits aren't entirely independent. Allthough it's possible to have any combination of hair/skin and eye-colour some combinations are extremely rare and will be however frequent racial mixing becomes

[darksphere]

Now I just have to post this allthough I'm not sure if I'm allowed to seeing as this chart isn't mine:

www.geocities.com/nationalanarkisme/eye_chart

It explains the genetics of eyecolour very well I think. Hair and skincolour works in basically the same way allthough substantially more complex.

[darksphere]

Graeme said:

That is a point. From my observations, a lot of blue eyed people have brown or yellow splodges in their iris and that their are a lot of mixed eyes colours like blue, green and brown though the overall effect may be blue or green or brown.

I've never experienced that(I haven't looked much for it either though). Sure nono or very few people have eyes with no variations. But these are variations in nuances. I've never seen anyone with both blue and yellow and brown eyes at the same time.

Maby the population in Australia is just very mixed...

Graeme said:

So all that fuss about eye colour when the actual colour can't be seen unless you are eyeballing them.

Even if the picture gets more complex when looking at people closely then you can see the overall colour in a glance. At least that is my experience.

In reality no two humans are entirely the same. Noone has exactly the same hair eye or skin colour. Or the same nose or the same build.

So why bother about physical anthopology at all?

Personally I see it like this: Human diversity is surely too enormous to be mapped or understood entirely. But that is not an argument not to try to uncover as much of the diversity as possible.

That a thing is too complex to be understood easily does not mean one shouldn't try to understand it as well as possible.

[Graeme]

What I said is true from my observations. The colour of the iris varies over its surface so some sectors may vary in intensity or colour. Light brown areas around the pupil of the iris in blue eyed people is common. In genetics the term mosaic is used for allelic variations expressing within the same individual. Iridology photographs are useful in seeing these colour variations in the iris.

Genetics is my field, albeit in microorganisms, and there is a thing called crossover where chromosomes in the process of replication and division to form a new individual break segments of the chromosomes from the female parent and from the male parent and interchange them. So the individual has chromosomes which are not only derived from the parents but shuffled in a unique way. In that process the linkage of light hair with light eyes can be broken where the parents are of different phenotypes or races. Thus a person can be blue eyed and dark brown haired or light haired and dark eyed.

[darksphere]

Graeme said:

. In that process the linkage of light hair with light eyes can be broken where the parents are of different phenotypes or races. Thus a person can be blue eyed and dark brown haired or light haired and dark eyed.

Sure. I only said that some combinations are substantially more common than others due to linkage. But of course the linkage can be broken.