Can two blue-eyed parents give birth to a brown-eyed child?

JustCoz

I was just wondering, I did Biology for my Leaving Cert. and thought that this was an impossibility but my friend says it can happen. Can anyone clear this up for me?

johnny_adidas

i can happen alright. google it. i remember finding stuff about it before

Shib

Eye color is an inherited trait influenced by more than one gene. In humans, three genes coding for eye color are currently known: EYCL1, EYCL2, and EYCL3. These genes account for three phenotypic eye colors (brown, green, and blue) in humans. Although it was once thought that brown eye color was always dominant and blue eye color was always recessive, the fact that two blue-eyed parents can give birth to a brown-eyed child has shown that the determination of eye color does not follow the simple rules of Mendelian inheritance, although this is so rare that scientists didn't even notice that it happens (perhaps 1 in 100,000,000) until recently. It is not like two brown haired parents who have a blonde haired child, because blonde and brown hair is the same gene pair. Eye color is the most demanding of any gene, due to the fact all four have to be a the same color or the eye color will not be pure, and will be mixed with each other (like blue-green).

edit: This is nicked direct from Wikipedia btw

Faith

This was all covered in PI not long ago.

The simple answer: Yes, they can.

See the PI thread here: http://pie.boards.ie/vbulletin/showthread.php?t=2055015819

JustCoz

Thanks! I'll check out the link

sudzs

I know of family where both parent have hazel (sorta brown!!) eyes and have a blue eyed daughter.

Kevster

Genetics rocks! In humans, brown eyes ARE dominant over blue eyes. The fact that both of these parents produced a blue-eyed child means that both of them had the dominant gene AND the recessive gene. Genes always come in pairs and one gene [The dominant] usually prevents the expression of the other [The recessive].

BB = Brown
Bb = Brown
bb = Blue

Sperm cells however only have one of the gene types - The oocyctes in the female ovaries are the same. So, what happened here is that a sperm cell with the 'b' gene combined with an oocyte with the 'b' gene also since that is the only combination that could result in blue eyes. Thus, the child now has both recessive forms of the gene: bb.

In basic Mendelian genetics, the reverse of this (Two blue-eyed parents giving birth to a brown-eyed child) cannot happen. It has been shown that it CAN happen however and the case that was decsribed in Shib's post could be explained by a mutation of a gene I guess.

This is the simplest of Mendelian crosses. Another trait in humans that is the same as this are ear-lobes: Whether or not the lobe is attached to your head or not (ie is loose).

Capt'n Midnight

Kevster wrote:

Genetics rocks! In humans, brown eyes ARE dominant over blue eyes. ...

It has been shown that it CAN happen however and the case that was decsribed in Shib's post could be explained by a mutation of a gene I guess.

The first line of Shib's post was

Shib wrote:

Eye color is an inherited trait influenced by more than one gene.

another linkie

http://www.seps.org/cvoracle/faq/eyecolor.html

The genetic basis for eye color is actually far more complex. At the present, three gene pairs controlling human eye color are known. Two of the gene pairs occur on chromosome pair 15 and one occurs on chromosome pair 19. The bey 2 gene, on chromosome 15, has a brown and a blue allele. A second gene, located on chromosome 19 (the gey gene) has a blue and a green allele. A third gene, bey 1, located on chromosome 15, is a central brown eye color gene.

Geneticists have designed a model using the bey 2 and gey gene pairs that explains the inheritance of blue, green and brown eyes. In this model the bey 2 gene has a brown and a blue allele. The brown allele is always dominant over the blue allele so even if a person is heterozygous (one brown and one blue allele) for the bey 2 gene on chromosome 15 the brown allele will be expressed. The gey gene also has two alleles, one green and one blue. The green allele is dominant to the blue allele on either chromosome but is recessive to the brown allele on chromosome 15. This means that there is a dominance order among the two gene pairs. If a person has a brown allele on chromosome 15 and all other alleles are blue or green the person will have brown eyes. If there is a green allele on chromosome 19 and the rest of the alleles are blue, eye color will be green. Blue eyes will occur only if all four alleles are for blue eyes. This model explains the inheritance of blue, brown and green eyes but cannot account for gray, hazel or multiple shades of brown, blue, green and gray eyes. It cannot explain how two blue-eyed parents can produce a brown-eyed child or how eye color can change over time. This suggests that there are other genes, yet to be discovered, that determine eye color or that modify the expression of the known eye color genes.

How does a gene, a section of a chromosome in the cell nucleus, make my eyes a particular color?

The exact color of the human eye is determined by the amount of a single pigment called melanin that is present in the iris of the eye. Melanin is a dark brown pigment that is deposited on the front surface of the iris. If a lot of melanin is present, the eye will appear brown or even black. If very little melanin is present the iris appears blue. Intermediate amounts of melanin produces gray, green, hazel or varying shades of brown. Genes work by directing the production of enzymes, chemicals that control all of the processes that occur in our body. Eye color genes, through the enzymes they produce, direct the amount and placement of melanin in the iris. In general Caucasian babies are born with blue eyes because at the time of birth they haven't begun to produce melanin in their irises. Their eyes may change to green, brown or other colors as melanin production begins. Babies of other ethnic origins such as African, Asian, Hispanic and Native American, are often born with brown or black eyes. Albinos have no pigment in their irises so the blood vessels in the back of the eye reflect light making the eyes look pink. Albinos also lack melanin in their skin and hair. Since albinism is caused by a recessive allele, two normal parents may produce an albino. An albino can have normal offspring if the other parent is normal for melanin production.

http://www.bbc.co.uk/dna/h2g2/A734933 - bit better explaination of physical basis for eye colours vs. melanin

r3nu4l

Very topical at the moment BBC News

Kevster

I was on my way here to post that link too. You beat me to it *shakes fist* It is VERY interesting research.

r3nu4l

Kevster wrote:

I was on my way here to post that link too. You beat me to it *shakes fist* It is VERY interesting research.

If it makes you feel better, I was going to post the link about 'Virgin birth' in Komodo dragons in AH but I was beaten to it that time

Kevster

...another very interesting article but not as much as the eye-colour story. So, you got to post the best story first

Aoife-FM104

OK then what about two white people having a mixed race child?

Kevster

Two white-skinned people can never produce a mixed-race child considering the two parents are of the same race. However, I think that you are referring to skin-colour. I know dark-skinned people that have been produced by two white skinned parents. They are not dark enough to be called 'black' but it is enough to be noticeable.

Dark-skin is due to the extra-production of the chemical 'Melanin'. Melanin is produced by Melanocytes which are cells that are found in skin. In fair-skinned people there is little Melanin produced.

Considering that skin-colour is only based on this one fact then it can be inferred that there is relatively little nucleic material involved in the coding for 'Melanocytes'. The less nucleic material involved in a trait, the greater the chance that the phentotype of the child will differ from that of their parents.

Prove me wrong someone - I don't feel confident on this answer!

Kevin.

Capt'n Midnight

Kevster wrote:

Prove me wrong someone - I don't feel confident on this answer!

CBA googling but IIRC at least 14 genes are responsible for skin colour or the so many factors are involved that it seems like 14. So what you get is a blending.

don't forget the effects of
sunshine
albinoism
parkinsons
fake tan
jaundice
lighting
and in the case of that famous front page with Time and Newsweek of OJ Simpson skin colour is also affected by photoshop

How do you define mixed race ?
there are more births in this country to women in their 40's than 20's (on the radio so it must be true) so the numbers of downs syndrome may increase
so are mongoloid children of a mixed race ?

Kwekubo

Capt'n Midnight wrote:

How do you define mixed race ?

Race is more a social classification than a scientific one, there is generally more variation between members of a specific "race" than between different ones. In my view race can mean more or less anything - black, white, Irish, French etc.

Victor

My mother has blue eyes, my father brownish. All my siblings have blue eyes, whereas I was born with brown eyes, that have changed over time, gaining green and blue sections.

Most of my hair is brown-black, but my beard is a mix of individual black, brown, blonde and red hairs.

Some of the genes for darker skin are recessive. Two pale skinned parents can give birth to a darker skinned child.

Capt'n Midnight wrote:

there are more births in this country to women in their 40's than 20's (on the radio so it must be true)

I thought its was more new mothers in their forties than in their teens.

Capt'n Midnight

Victor wrote:

I thought its was more new mothers in their forties than in their teens.

yeah you're probably right

sudzs

Considering we all originate in Africa it's completely possible that "white" parents could have a "black" child.... allbeit very rare indeed!

Victor

sudzs wrote:

Considering we all originate in Africa it's completely possible that "white" parents could have a "black" child.... allbeit very rare indeed!

I could also give birth to some fish-like creatures, albeit unlikely, what with me being male.

If enough generations have gone by, then some people may have no "black" genes left

sudzs

... and equally some may have "black" genes left.

Take Jade Goody for example... She is mixed race, as she said herself the other day. (not that I watch that Big Brother crap!!! )At a glance you'd be hard pushed to come to the conclusion that she had any black genes at all... even though her father is part African AFAIK.

Not sure where I'm going with this!!! Except that I remember years ago there was an Irish couple on either the Late Late (with Gaybo) or Prat Kennys chat show, and they had a baby boy who was so African looking it was unreal!!! They were from Mayo I think... anyone remember that??

So I supose with genetics anything is possible! (NOT giving birth to some fish-like creatures though!!!)

Capt'n Midnight

What about surrigate mothers ?
or gene therapy

since it's just pigment levels in the eyes it might be changable by hormone treatment.

sudzs

Capt'n Midnight wrote:

What about surrigate mothers ?
or gene therapy

since it's just pigment levels in the eyes it might be changable by hormone treatment.

Or a bang on the head...

Look at David Bowie's eyes!

(Happy Birthday David!!! )

Capt'n Midnight

oh yeah sheeps eyes,

sudzs

Capt'n Midnight wrote:

oh yeah sheeps eyes,

:eek: :eek: :eek: