Major Medical Boo Boo on Mars

[ghostjmf]

Going to spoilerize this for all who haven't watched last night's episode, but intend to eventually:

Spoiler

Last night(3/4/09)'s episode hinged on a kid being identified as the child of her real father
by having one blue eye & one brown eye, just like the father.

Problem is, as far as I know, this isn't an inheritable trait. You'd think the network could have loaned some story-vetting staff from a medical show (except ABC's medical shows are Grey's & Practice; that explains it!).

Now, we know brown eye-pigment genes are dominant; one brown-eyed parent will dictate you have brown eyes.

I always assumed that people with one brown eye & one lighter-colored eye (green or blue or gray) had some problem with pigment production in one eye. A pigment production problem could be genetic, but if so would be much more likely to affect both eyes, so my guess is that the odds of a kid, even if they have inherited the same genetic pigment-production problem, having it display itself in one & not both (or neither) eye is very unlikely.

An early-development mutation in the development of pigment-production genes in one eye could also cause the color difference, but, again, the likelihood of a child developing, rather than inheriting, the same not-born-with-it mutation their father had is almost zero.

But recently I saw yet another show ("ReGenesis", one that usually has its science well vetted) where someone was identified as a chimera because they had one blue & one brown eye. A chimera in human genetic terms is someone who has a different DNA signature in different part of their body; its explained by the live person being produced by a set of fraternal twins where one got absorbed into the other at an early stage. Still doesn't explain why, since both twins have the same 2 parents, they both don't have the same eye-color, because "brown is dominant".

Oh well.

I guess you could have a case, very rare or impossible in people though documented in animals, of each twin being the child of a different father. Blue-eyed woman with one blue-eyed boyfriend, followed very closely by brown-eyed boyfriend; theoretically possible, but I don't know if this has ever been documented in humans. Fertilized human eggs produce hormones to prevent subsequent eggs from getting fertilized.

But even if you explain the eye-color thing in a chimera; that chimera's child is not going to be another chimera. Being a chimera is not an inheritable trait. I don't think.

Gotta go home now & watch more TV!

[TheCalvinator24]

2 Brown-eyed parents have blue-eyed children all the time.

[themanintheseersuckersuit]

Spoiler

Heterochromia

[jaybee]

Now, we know brown eye-pigment genes are dominant; one brown-eyed parent will dictate you have brown eyes.

![/spoiler]

I sure hope not.

I am brown eyed. Mrs Jaybee is green eyed.

Son #1 has brown eyes
Son #2 has green eyes
Son #3 has blue eyes

Our mailman is a woman.

?????????????

[BackInTex]

Now, we know brown eye-pigment genes are dominant; one brown-eyed parent will dictate you have brown eyes.

No. A brown-eyed parent gives a child a 50% chance of being brown-eyed.

Two brown-eyed parents give a child a 75% chance of being brown-eyed.

My mom was brown-eyed, 3 kids, 1 green, 1 hazel, one blue.

My dad had green eyes.

Can't tell if my Mom's non-brown gene was blue or hazel, unless hazel is dominant to green then hers was hazel.

two blue eyed parents guarantee a blue-eyed child.


At least that is my understanding.

[mrkelley23]

That's better, but still not the bottom line. I blame high school biology teachers who reduce everything to fractions. If eye color were truly linked to only the one gene, then two parents who had both dominant "brown" genes could only have browneyed children. And those children would all be both-dominant browns.

A double-dominant brown with a single dominant brown would still have all brown-eyed children, but some of them could be double dominant and some could be single dominant.

Two single dominant browns could have blue-eyed children (as was the case with my parents, who both had brown eyes but produced two brown-eyed children and two blue-eyed children).

Two blue-eyed parents should always have blue eyed children, according to the single-gene, no mutation high school biology probability model.

But, as with most things in life, it just ain't that simple. For one thing, the SGNMHSBPM doesn't take into account colors other than blue or brown. It doesn't take into account the fact that multiple genes can play a role in eye color, nor the fact that mutation plays a role as well.

[TheCalvinator24]

Now, we know brown eye-pigment genes are dominant; one brown-eyed parent will dictate you have brown eyes.

No. A brown-eyed parent gives a child a 50% chance of being brown-eyed.

Two brown-eyed parents give a child a 75% chance of being brown-eyed.

My mom was brown-eyed, 3 kids, 1 green, 1 hazel, one blue.

My dad had green eyes.

Can't tell if my Mom's non-brown gene was blue or hazel, unless hazel is dominant to green then hers was hazel.

two blue eyed parents guarantee a blue-eyed child.


At least that is my understanding.

A brown-eyed person can carry any of the following combinations:
Brown/Brown (if this is the case, all of the person's children will have brown eyes)
Brown/Blue
Brown/Green
Brown/Hazel

If 2 Brown-eyed parents who are both Bb (Brown/blue), each could transmit the b instead of the B, giving the offspring blue eyes.

My wife and I both have hazel eyes. Two of our children have hazel eyes, and two have blue eyes. It is obvious that we are both Hb

this is an oversimplification, but it should demonstrate why saying tha two brown-eyed parents alwasy produce brown-eyed offspring is completely wrong.

[ToLiveIsToFly]

Now, we know brown eye-pigment genes are dominant; one brown-eyed parent will dictate you have brown eyes.

No. A brown-eyed parent gives a child a 50% chance of being brown-eyed.

Two brown-eyed parents give a child a 75% chance of being brown-eyed.

My mom was brown-eyed, 3 kids, 1 green, 1 hazel, one blue.

My dad had green eyes.

Can't tell if my Mom's non-brown gene was blue or hazel, unless hazel is dominant to green then hers was hazel.

two blue eyed parents guarantee a blue-eyed child.


At least that is my understanding.

Well it's not quite that simple.
A brown eyed parent has at least one brown eye gene. But we don't know what the other genes. Some parents will be brown-brown, and some parents will be brown-something else. Let's call the probability that the second gene is also brown X.

One parent having brown eyes means the probability of a child having brown eyes is 50% + X
Two parents having brown eyes means the probability of a child having brown eyes is 1 - (1 - 50% - X)^2

Unless I screwed up the math.

[Weyoun]

According to that horror movie that came out recently (The Unborn), this means that the kid has a demon twin living in him. Better be careful!

[silverscreenselect]

It's kind of tough to insist on medical accuracy on a show in which a guy travels 35 years into the past and frequently has people on television talk directly to him.

[wintergreen48]

That's better, but still not the bottom line. I blame high school biology teachers who reduce everything to fractions. If eye color were truly linked to only the one gene, then two parents who had both dominant "brown" genes could only have browneyed children. And those children would all be both-dominant browns.

I went to college as a biology major with a strong interest in genetics (although I planned eventually to go to law school, which is of course what I ultimately did). I was exempt from the usual foreign language requirement, having tested out based upon languages I had already learned, so naturally I enrolled in the Honors German program as an elective. I wanted to be able to read Mendel in the original German; my biology advisor thought I was nuts. Well. It seems that the good friar was not entirely the upright man of God that one might expect: he fudged his results.

Like Kepler (who spent his life trying to reconcile the 'imperfect' ellipse with his preconception that God MUST have ordained that the planets orbit in geometrically perfect patterns), Mendel seems to have been absolutely convinced that genetics was a matter of perfect fractions, and if his peas didn't bloom consistent with perfect fractions, well, by gosh, that's why pencils have erasers on them. So this 'rounding' thing, that suggests that genes link up in perfect order (if Brown = B and blue = b, a BB mother and BB father, both of whom have brown eyes, will always have only BB children, all of whom will be brown-eyed; a bb mother and bb father will always have only bb children, all of whom will be blue-eyed; a BB mother with brown eyes and a Bb father with brown eyes will always have only brown-eyed children, 1/2 of whom will be BB and 1/2 of whom will be Bb; a Bb mother and a Bb father, both with brown eyes, will always have a mixture of children, 1/4 of whom will be brown-eyed BB, 1/4 of whom will be blue-eyed bb, and 1/2 of whom will be brown-eyed Bb), well, it didn't start in modern high school biology class, it goes back to the founder hisself, Gregor Mendel.

[MarleysGh0st]

I enrolled in the Honors German program as an elective. I wanted to be able to read Mendel in the original German; my biology advisor thought I was nuts. Well. It seems that the good friar was not entirely the upright man of God that one might expect: he fudged his results.

You learned that by reading him in the original German? Had the English translators been in a conspiracy to keep it secret?

[wintergreen48]

I enrolled in the Honors German program as an elective. I wanted to be able to read Mendel in the original German; my biology advisor thought I was nuts. Well. It seems that the good friar was not entirely the upright man of God that one might expect: he fudged his results.

You learned that by reading him in the original German? Had the English translators been in a conspiracy to keep it secret?

That's why my advisor thought I was nuts-- everything important that Mendel did was already available in English translations. The results fudging business is only implied, though: his 'rules' of heredity are pretty precise, and his results all confirm the rules, but no one gets absolutely perfect results, every single time, except, of course MBFFB who is never wrong about anything.

[ghostjmf]

OK, as my brain cleared in the cold night air on the walk home, to where there is no computer, I remembered that because "brown is dominant", a brown-eyed parent, one of whose own parents had blue eyes, will still be carrying one chromosome each coding for each eye-color, "brown" vs "light". So if their germ plasm (sperm or egg) with the "light" gene meets up with their mate's germ plasm (sperm or egg) with a "light" gene, the offspring's eyes will be light.

I really would have run back here & self-corrected this, because spacing on it makes me feel really stupid, but Boubacar Diabate & Samba Loco were waiting (at Johnny D's, to give a great show, not for me personally. But anyway.).

Spoiler

So you don't really need the far-fatched scenario of human fraternal twins with 2 different fathers, probably an impossibility (in humans; its been documented in some animals) to create a chimera who gets a light eye from one of the twins & a brown eye from the other.

But, heredity-statistics brain-clogs of mine aside, the basic premise I put out there, that "being a chimera" is not an inheritable trait, but rather an accident that happens during gestation (well, since we're talking humans, lets just call it pregnancy!) still holds.


So the human chimera father with the one brown eye & one blue eye would not have anything in his sperm cells dictating that his child would have one brown eye & one blue eye.

And if the kid (or the father) developed this feature as the result of some problem with pigment production, rather than "because they're a chimera", there is very little chance that the kid, even with a pigment production problem, would have it expressed in their metabolism in exactly a way that would give them "one brown eye, one light eye".

There are a lot of traits that really are predictably genetic, & even so rare that even "way back in the dawn of time, 1973" per the show, geneticists could have said "this pair is parent & child". But they aren't so striking to look at as the "one brown eye, one blue" used, incorrectly, on the show.

[VAdame]

So this 'rounding' thing, that suggests that genes link up in perfect order (if Brown = B and blue = b, a BB mother and BB father, both of whom have brown eyes, will always have only BB children, all of whom will be brown-eyed; a bb mother and bb father will always have only bb children, all of whom will be blue-eyed; a BB mother with brown eyes and a Bb father with brown eyes will always have only brown-eyed children, 1/2 of whom will be BB and 1/2 of whom will be Bb; a Bb mother and a Bb father, both with brown eyes, will always have a mixture of children, 1/4 of whom will be brown-eyed BB, 1/4 of whom will be blue-eyed bb, and 1/2 of whom will be brown-eyed Bb),

Whereas in reality, it's more like the old "flipping the coin" situation. If you flip a coin and it comes up heads 9 times, what are the chances it'll come up tails on the 10th? Still 50-50!

Assuming no 2-headed coins, tricks w/ weights, etc....the odds re-start for each flip.

The odds of any eye color re-start for each pregnancy. So each child has the same chance of BB, bb, or Bb, whether the couple has one child or 10 children.

Me, hazel. First husband, light brown. Kid, blue (one slightly more green!)
Second husband, deep dark brown. One kid light brown, one kid deep dark brown.

My parents: Mom, hazel, Dad, blue-gray. 5 kids, one hazel, one blue-gray, one bright blue, 2 more hazel.

[wintergreen48]

OK, as my brain cleared in the cold night air on the walk home, to where there is no computer, I remembered that because "brown is dominant", a brown-eyed parent, one of whose own parents had blue eyes, will still be carrying one chromosome each coding for each eye-color, "brown" vs "light". So if their germ plasm (sperm or egg) with the "light" gene meets up with their mate's germ plasm (sperm or egg) with a "light" gene, the offspring's eyes will be light.

Good thing I am not OCD man, because then I would feel compelled to point out that it is 'genes,' not 'chromosomes,' that control eye color (which is kind of ironic, since 'chromosome' comes from Greek for 'color body').

[ghostjmf]

wintergreen says:

Good thing I am not OCD man, because then I would feel compelled to point out that it is 'genes,' not 'chromosomes,' that control eye color (which is kind of ironic, since 'chromosome' comes from Greek for 'color body').

It its genes, which are areas on chomosomes. When talking one trait, I tend to use the terms interchangeably, though, as you point out, incorrectly. I agree that the chromosome with the eye-color gene on it has plenty other genes on it too.

One chromosome in a pair of "chromosomes that carry genes that code for the same traits" will carry the gene that codes for "brown", one will carry the gene that codes for "light", & the kid only gets one chromosome of the pair from each parent.

[ne1410s]

I now have strabismus from reading this thread...

[frogman042]

...Snip....

Spoiler

So you don't really need the far-fatched scenario of human fraternal twins with 2 different fathers, probably an impossibility (in humans; its been documented in some animals) to create a chimera who gets a light eye from one of the twins & a brown eye from the other.
...Snip...

Spoiler

If memory serves me correctly, that case occurred, I think on an army base in Germany. I think the two fathers were of different races, and the two children showed different race characteristics.

A quick google search confirms that it not only is it not impossible in humans - it occurs more frequently than I thought (although still very rare).

[tanstaafl2]

Spoiler

Heterochromia

What the show appeared to be showing was what suit guy noted here and not having to do with the many different genes responsible for the degree of pigmentation in the iris.

Complete heterochromia, more typically seen in cats and dogs than people, is autosomal dominant so that if you have one of the 2 genes responsible for the trait it will be manifest and gives a (presumably roughly, given Mendel's apparent fudgy nature...) 50% chance of it being present in offspring.

While I have seen sectoral heterochromia from both genetic and other causes on many occasions, pictures of genetic complete heterochromia and a case or two of complete heterochromia resulting from a disease I have never personally seen a case of genetic complete heterochromia.

And I've been looking...


Kate Bosworth is the one present day "famous" person I knew of that had it but hers is only sectoral.


Turns out, according to a list on Wiki, so does SAB pitcher Max Scherzer and his appears to be complete. I assume it is the benign genetic form but don't know for sure. Definitely kinda odd looking though!


A couple of the other contemporary people on the wiki list don't appear to have it or it is sectoral and/or mild from pictures I can find.

[ghostjmf]

OK, I bow to the supremacy of the genetics here. There really is an inheritable condition that will give you eyes each a different color. And here I went through life (until now) thinking it was either due to a metabolic problem (which could be genetically dictated, but didn't have to be) affecting the lighter eye, or the result of an after-birth mutation, or, if you watch too much science-inspired TV, being a human chimera!