How can brown-eyed parents have blue-eyed children?

Pithikos

I am learning about genes and heritage currently and I am a bit baffled about something.

In my book it states that in a plant's gene, if S is for smooth leaves and s for rough leaves, then we get these combinations:

Code:

Parent plant | Child plant | Dominant alleles
S + s       ->     Ss     ->     S
s + S       ->     sS     ->     S
S + S       ->     SS     ->     S
s + s       ->     ss     ->     s

So the only way to get a plant with smooth leaves is if both parents have the recessive gene s.

But what happens when it comes to eye color? If we say that for brown eyes we have B and for blue eyes we have b then how can we get blue eyed children from brown eyed parents? For example:

Code:

Parent      |    Child     |  Dominant alleles
B + b      ->     Bb      ->     B
b + B      ->     bB      ->     B
B + B      ->     BB      ->     B
b + b      ->     bb      ->     b

So the only way for a kid to get blue eyes is the two parents have blue eyes, according to my table. In any other case the kid has brown eyes.

This ofcourse is wrong as I know families where the parents have brown eyes and some of their children have blue eyes. So where did I do wrong?

phyzguy

Each parent has two alleles, with the brown eyed B dominant, not just one as in your table. So the way brown-eyed parents have a blue-eyed child is as follows:

Mother - Bb Father Bb Possible Children BB, Bb, bB, bb

The bb combination will have blue eyes. Can blue-eyed parents have a brown-eyed child?

Ryan_m_b

Note that eye colour isn't just determined by one gene. In simple models it can be represented by two genes: one governing brown/blue and one green/blue with dominance being a hierarchy of brown > green > blue but in reality it's more complicated than that. There are a wide variety of genes involved in the formation of the eye that dictate eye colour.

Velikovsky

A quarter of children born to brown eyed parents who both posses blue allele will have blue eyes.
Blue eyed parents can have brown eyed kid's!
http://genetics.thetech.org/how-blue...-eyed-children

Ryan_m_b

Quote by Velikovsky

A quarter of children born to brown eyed parents who both posses blue allele will have blue eyes.
Blue eyed parents can have brown eyed kid's!
http://genetics.thetech.org/how-blue...-eyed-children

Fascinating, I never realised that blue eyes were a result of Rayleigh scattering of reflected light.

Velikovsky

Quote by Ryan_m_b

Fascinating, I never realised that blue eyes were a result of Rayleigh scattering of reflected light.

Fascinating indeed! I also often think of that couple by the Black Sea 6000 years ago when they first looked in to their newborn baby boys blue eyes and what they would have thought of his and their 1.2 billion direct descendants? Depending were in the world you are they seem to be getting rarer. But here in Ireland were there has been little immigration for over 2000 years blue eyes make up 96% of the population!

Borek

Quote by Velikovsky

I also often think of that couple by the Black Sea 6000 years ago when they first looked in to their newborn baby boys blue eyes and what they would have thought

What is surprising in the newborn having blue eyes? They all do, eye color changes much later.

Monique

Quote by Velikovsky

A quarter of children born to brown eyed parents who both posses blue allele will have blue eyes.
Blue eyed parents can have brown eyed kid's!
http://genetics.thetech.org/how-blue...-eyed-children

That's good to know, I didn't know that could happen

Velikovsky

Quote by Borek

What is surprising in the newborn having blue eyes? They all do, eye color changes much later.

All of them!!! Most Jewish people of Kazakh/Ashkenazi decent such as myself are born with dark brown or even black eyes. Not to mention most African races south of the Sahara. Newborn brown eyes also occur among native Americans/Asians/Hispanics. And yes evenwhite Europeans occasionally!!

Velikovsky

Quote by Monique

That's good to know, I didn't know that could happen

It is good to know Monique, there are so many superstitions and old wives tales when it comes to eye colour!

Huastecan

It is because is a Mendelian trait; if both parents have the b gene, even if they are brown eyed they may have blue-eyed children, as it is recessive. As far as I remember, the percentages are: 25% brown eyed children, 50% Bb, and 25% bb, that is, blue eyed children.

Pithikos

Quote by phyzguy

Each parent has two alleles, with the brown eyed B dominant, not just one as in your table. So the way brown-eyed parents have a blue-eyed child is as follows:

Mother - Bb Father Bb Possible Children BB, Bb, bB, bb

The bb combination will have blue eyes. Can blue-eyed parents have a brown-eyed child?

Ok, but if each parent has 2 alleles, then we have a total of 4. How are only two alleles chosen from those 4 for the child? Is it a random choice?

Ryan_m_b

Quote by Pithikos

Ok, but if each parent has 2 alleles, then we have a total of 4. How are only two alleles chosen from those 4 for the child? Is it a random choice?

One allele is on each chromosome and each parent gives their child one chromosome. It's a bit more complicated than that but is this what you're asking?

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phyzguy	Each parent has two alleles, with the brown eyed B dominant, not just one as in your table. So the way brown-eyed parents have a blue-eyed child is as follows: Mother - Bb Father Bb Possible Children BB, Bb, bB, bb The bb combination will have blue eyes. Can blue-eyed parents have a brown-eyed child?

Ryan_m_b Mentor Blog Entries: 1	Note that eye colour isn't just determined by one gene. In simple models it can be represented by two genes: one governing brown/blue and one green/blue with dominance being a hierarchy of brown > green > blue but in reality it's more complicated than that. There are a wide variety of genes involved in the formation of the eye that dictate eye colour.

Velikovsky	How can brown-eyed parents have blue-eyed children? A quarter of children born to brown eyed parents who both posses blue allele will have blue eyes. Blue eyed parents can have brown eyed kid's! http://genetics.thetech.org/how-blue...-eyed-children

Huastecan	It is because is a Mendelian trait; if both parents have the b gene, even if they are brown eyed they may have blue-eyed children, as it is recessive. As far as I remember, the percentages are: 25% brown eyed children, 50% Bb, and 25% bb, that is, blue eyed children.