Genetics and Paternity

I have a couple of questions about paternity.

Say a blue eyed mother and a (possible) brown eyed "father" had a baby and the baby came out blue eyed, what are the chances of the brown eyed father being the actual father of the baby?

Say a blue eyed mother and a (possible) blue eyed "father" had a baby and the baby came out blue eyed but a brown eyed man thinks he is the father and the blue eyed baby 'smells right' to the (possible) blue eyed "father", which is most likely the real father?

I don't know much about genetics and I'm trying to figure this one out!

It’s complicated
www.answers.com...

Genetics of Eye Color

Differences in iris color have been attributed to such causes as the temperature of the brain and eyes. Some people have stressed differences between dark-eyed and light-eyed populations and have suggested that eye color is related to general traits such as temperament or intellect. But, toward the middle of the nineteenth century, it had become clear that iris color was due to iris pigment, that this pigment developed soon after birth, and that the final quantity and distribution of the pigment was a hereditary trait.

Originally, iris color was thought to be a simple trait—one governed by a single gene with multiple forms, or alleles, corresponding to each color. In this scheme, blue was thought to be recessive, requiring two copies of the blue allele in order to be displayed. Therefore, two blue-eyed parents could have only blue-eyed children, since each parent had only blue alleles. However, repeated observation of brown-eyed offspring from two blue-eyed parents showed this view to be wrong. Iris color is likely to be a polygenic trait—one governed by at least two genes and possibly more.

Brown versus blue eye color is believed to be controlled by two genes on chromosome 15, called BEY1 and BEY2. Green versus blue eye color is believed to be controlled by a gene on chromosome 15, called GEY. In this system, blue is believed to be recessive to both brown and green. The protein products of these genes are unknown, however, as is the number of alleles possible for each. Furthermore, these three do not fully explain inheritance of all eye colors. More genes, which likely modify the action of these three, are probably involved.

From what I understand, brown eyes are a dominant gene, so it is likely that the mother cheated with a blue-eyed man, but it is not guaranteed. I'm not sure what the actual statistics would be. However, the very fact that blue-eyed people still exist must mean that it is possible in this given scenario for the baby to be blue-eyed and the father be brown-eyed.

The other thing to keep in mind is that I've also read that some babies are born with lighter coloured eyes like blue, but as they get older, the eyes gradually darken, so don't jump to conclusions too early.

The last thing to keep in mind is I'm not a geneticist :p But from things I remember reading, my words are correct to the best of my knowledge.

reply to post by DragonsDemesne

The last thing to keep in mind is I'm not a geneticist

Yea, me neither which is why I'm asking. Eye color just seems very confusing. Some sites say it's possible for a brown eyed and blue eyed couple to have a blue eyed baby and others say it's not. Haven't found a decent enough explanation behind it to explain why a brown eyed and blue eyed couple would have a blue eyed baby if brown is mostly the most dominant color.

Its not uncommon at all for 1 brown eyed parent to and one blue eyed parent to have a blue eyed baby. I can think of tons of people this as happened to. What I found odd is the high rate of 2 brown eyed parents having blue eyed children.

Originally posted by calstorm
Its not uncommon at all for 1 brown eyed parent to and one blue eyed parent to have a blue eyed baby. I can think of tons of people this as happened to. What I found odd is the high rate of 2 brown eyed parents having blue eyed children.

Was just about to say, my brother & sister in law are both brown eyed, and their daughter is blue eyed. She's 2, and it doesnt look like they are going to turn brown like they initially thought.

Maybe the baby's eyes haven't changed to their true colour, depending on its age? Would it matter if they eyes aren't brown, but more hazel? I love how people jump to the mother cheating all because of eye colour!

ill be able to tell you in 6 months personally, because i'm blue eyed, my partner is hazel eyed, so stay posted and ill let you know if i 'cheated' or not . (ps. I didnt)

Originally posted by DragonsDemesne
From what I understand, brown eyes are a dominant gene, so it is likely that the mother cheated with a blue-eyed man, but it is not guaranteed. I'm not sure what the actual statistics would be. However, the very fact that blue-eyed people still exist must mean that it is possible in this given scenario for the baby to be blue-eyed and the father be brown-eyed.

The other thing to keep in mind is that I've also read that some babies are born with lighter coloured eyes like blue, but as they get older, the eyes gradually darken, so don't jump to conclusions too early.

The last thing to keep in mind is I'm not a geneticist :p But from things I remember reading, my words are correct to the best of my knowledge.

I know most people seem to agree with this concept, but I'm going to throw a monkey wrench in here.

Both of my parents (biological) had brown eyes. My brother and I (same parents) both have blue eyes. My son has blue eyes, and his father has brown eyes, but again; my eyes are blue.

Sometimes, these things seriously don't make sense....

Just my .02 cents.

A_L

Originally posted by sirnex

Say a blue eyed mother and a (possible) brown eyed "father" had a baby and the baby came out blue eyed, what are the chances of the brown eyed father being the actual father of the baby?

A brown eyed father and a blue eyed mother could very easily have a blue eyed baby. Because the brown eyed father could have recessive blue eyed genes. (Over simplified on purpose)

Originally posted by sirnex
Say a blue eyed mother and a (possible) blue eyed "father" had a baby and the baby came out blue eyed but a brown eyed man thinks he is the father and the blue eyed baby 'smells right' to the (possible) blue eyed "father", which is most likely the real father?

The blue eyed father and the brown eyed father have about the same chance based on eye color alone. If the blue eyed father has a very good sense of smell, it is possible that he is picking up on something else, but I dont know any science on that.

I would say, a DNA test is in order to solve the thing once and for all. The eye color just isnt going to sort it on this one.

reply to post by sirnex

what are the chances of the brown eyed
father being the actual father of the baby?

As I understand it, people have multiple genes that determine eye color.

To give a simplified example:

Mother
Blue eye gene
Blue eye gene

Father
Blue eye gene
Brown eye gene

The mother has a pair of blue eye genes, so her phenotype is blue eyes. The father does have one blue eye gene, but the brown eye gene is dominant, so his phenotype will be brown eyes.

Now...they have a child. Both father and mother each give one of their eye gene to the child. Both of the mothers genes are for blue eyes, so she will always pass on a blue eye gene to the child. The father however, has two different genes, so it's 50/50 which gene he will contribute to the child. If he gives the blue eye gene, the child will have two blue eye genes, and thus will have blue eyes. But if the father contributes a brown eye gene, the child will have one of each, just like the father, and then will have brown eyes even though he has one gene for blue eyes.

what are the chances of the brown eyed father being the actual father of the baby?

There's not enough information in your scenario to answer that for certain, because phenotype alone isn't enough information to know what recessive genes he has. If he has a recessive blue eye gene, then the odds are 50/50. If he doesn't, then the odds are zero.

Though as others have pointed out, this is a simplified example. There may be more than two genes detrmining eye color.

Does the brown eyed father have any relatives (parents, grandparents, etc.) with blue eyes? It's possible there is a recessive gene floating around that simply didn't show.

reply to post by another_lurker

Both of my parents (biological) had brown eyes. My brother and I (same parents) both have blue eyes. My son has blue eyes, and his father has brown eyes, but again; my eyes are blue.

Presumably both your parents have recessive blue eye genes. One blue and one brown, just like the father above. They both contributed their recessive gene, and then you have blue eyes. Working with the two-gene simplified model above, the odds of that happening would be one in four.





[edit on 21-1-2010 by LordBucket]

reply to post by Illusionsaregrander

A brown eyed father and a blue eyed mother could very easily have a blue eyed baby. Because the brown eyed father could have recessive blue eyed genes. (Over simplified on purpose)

What if both his parents are brown eyed?

The blue eyed father and the brown eyed father have about the same chance based on eye color alone. If the blue eyed father has a very good sense of smell, it is possible that he is picking up on something else, but I dont know any science on that.

I threw that in there because I remembered reading something on pheromones awhile back ago. The reason we don't mate with our own siblings is because they 'don't smell right' and one of the reasons a father doesn't kill his baby is because it 'smells right', or something along those lines. It was a really long time ago, so I might not be remembering it right and I haven't looked it up since then.