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euclid
04-13-2011, 03:43 PM
Is it possible for one twin to have brown eyes, the other blue?

These are brother and sister.

shaldna
04-13-2011, 03:58 PM
In non identical twins, yes. But both parents would need to be carrying a blue gene as it's not a dominant colour.

So, in order to get a blue and a brown eyed child, the most common way would be if one parent had blue eys and the other had brown, or both had brown and were carriers of a blue gene.

Think of it like this, where b is a blue gene and B is a brown. In the example below the father has two b genes, so he has blue eyes (cause you need two in order to have blue eyes) and the mother has brown, because her one brown gene is dominat over her one blue gene.

So you can see from the chart that the options they have in eye colour for their children.

You can also work this out for other colours and combinations.


http://scienceaid.co.uk/biology/genetics/images/mono.png

http://scienceaid.co.uk/biology/genetics/images/mono.png

Selah March
04-13-2011, 04:04 PM
A pair of twins that is of mixed gender is by definition fraternal, as opposed to identical. Identical twins are formed from a single ovum and sperm which then splits, while fraternal twins are formed from two distinct ova and sperm. Therefore, yes, it is entirely possible for fraternal twins to have differing eye colors -- or to look almost nothing alike, in fact. However, as Shaldna stated, each parent would have to carry the recessive blue gene for one of the twins to have blue eyes.

fourlittlebees
04-13-2011, 04:08 PM
In non identical twins, yes. But both parents would need to be carrying a blue gene as it's not a dominant colour.

So, in order to get a blue and a brown eyed child, the most common way would be if one parent had blue eys and the other had brown, or both had brown and were carriers of a blue gene.

Think of it like this, where b is a blue gene and B is a brown. In the example below the father has two b genes, so he has blue eyes (cause you need two in order to have blue eyes) and the mother has brown, because her one brown gene is dominat over her one blue gene.

So you can see from the chart that the options they have in eye colour for their children.

You can also work this out for other colours and combinations.


http://scienceaid.co.uk/biology/genetics/images/mono.png

http://scienceaid.co.uk/biology/genetics/images/mono.png

Yes, one twin can have blue and one can have brown if they aren't genetically identical. But the bit about blue recessive, brown dominant that most of us learned in school isn't technically correct.

Explanation of eye color: http://www.thetech.org/genetics/ask.php?id=29

BTW, I had to relearn this myself when my green-eyed sister and blue-eyed brother-in-law had my brown-eyed nephew. :)

shaldna
04-13-2011, 04:22 PM
Yes, one twin can have blue and one can have brown if they aren't genetically identical. But the bit about blue recessive, brown dominant that most of us learned in school isn't technically correct.

Explanation of eye color: http://www.thetech.org/genetics/ask.php?id=29

BTW, I had to relearn this myself when my green-eyed sister and blue-eyed brother-in-law had my brown-eyed nephew. :)

It's what I learned at university too, it's basic, but it answered the question that the OP wanted to know without getting into the complicated genetics

crunchyblanket
04-13-2011, 04:29 PM
Yes. My twin brother has brown eyes and I have blue eyes.

euclid
04-13-2011, 04:45 PM
Thanks, everyone. That's exactly what I was looking for and just the level of complication I can handle!

MeretSeger
04-14-2011, 03:32 AM
Eye color is no longer considered a Mendelian trait.

Your twins can have this combination of eye color.

veinglory
04-14-2011, 03:39 AM
It's not a strictly Mendelian trait, but still tends to run pretty close to those proportions.

jaksen
04-14-2011, 08:04 PM
Eye color is no longer considered a Mendelian trait.

Your twins can have this combination of eye color.

So you can't use a Punnet Square to explain it. It is controlled by multiple alleles. The article cited above is excellent.

I have hazel (green-brown) eyes. Husband has brown. All three of my children have diff. eye colors: Blue, brown and hazel.

My mother has brown eyes; both her parents were blue eyes.

Hair color is also sort of complicated.

pezie
04-14-2011, 08:15 PM
Yes, boy-girl twins can have different color eyes. Also, that combo. is possible (as others have stated). I just wanted to chime in b/c I have boy-girl twins :).

But, for what it's worth. I have brown eyes, my husband has hazel eyes. Our first son has brown eyes. Both of our twins have blue eyes. Since boy/girl twins are no more genetically similar than any other set of siblings, it's possible for them to have the eye color combo. presented here.

DavidZahir
04-14-2011, 10:50 PM
Is it possible for one twin to have brown eyes, the other blue?

These are brother and sister. Yes.

JoNightshade
04-14-2011, 10:54 PM
When I was little I had this picture book about a pair of identical boy/girl twins. I always thought that would be so fun to have! Later, when I found out this was not possible, I was crushed! :D