According to http://www.dailymail.co.uk/news/arti...ite-twins.html ,
two "mixed" people can have kids who vastly differ in skin tone. However, for instance, Chinese all have sort of a light tan, then how come they never have kids who are really light in skin tone? Is it because they don't have the "white" skin gene?

PS: notice I used the PC word of skin tone, instead of skin color, to represent a continuum in skin pigmentation from fair to almost black.

Let's assume you've got a capital-letter race and a lowercase-letter race, and we're tracking 8 genes. People who are "purely" one race or another would be either AABBCCDDEEFFGGHH or aabbccddeeffgghh. A couple in which one person was from one race and the other was from the other race would have children who were perfectly heterozygous on each of 8 relevant genes: AaBbCcDdEeFfGgHh.

Now, take two of those "mixed" people and consider what genomes they could produce together. Suddenly, every imaginable combination is within the realm of possibility, if not equally likely. Just on the first gene alone, the children could inherent capitals from both parents (AA, 25% chance), lowercases from both parents (aa, 25% chance), or capital from one and lowercase from the other (Aa, 50% chance). The same goes for every other gene we're considering (BB, bb, Bb; CC, cc, Cc...). The most likely outcome is a perfectly heterozygous mix again or something close to it. But, as unlikely and rare as it would be, perfectly homozygous results (matching the genomes of the original pure races) are also possible from the mixed parents.

If a child in such a family got AABbCcDdeeFfGgHH, (s)he would be homozygous capital for two of these genes (A and H), homozygous lowercase for one (e), and heterozygous for all of the rest, and would normally be considered "mixed" overall. But one who somehow managed to inherit only aabbccddeeffgghh from his/her mixed parents, or probably even as close to it as aabbccDdeeffgghh, would be dramaticly reported as simply a member of the lowercase race with mixed parents.

In reality, there are a lot more genes associated with race than this, so homozygosity on all or even most of them gets pretty stupendously unlikely even if the parents are both exactly 50/50 themselves... so unlikely that it essentially never happens and the various "pretty close to even split" combinations add up to almost all of the real-world results. Even in this case, what really happened isn't even a matter of getting a black (or even mostly-black) baby and a white (or even mostly-white) baby from mixed parents by the kind of statistical rarity I described above. The darker baby is no darker or less mixed than her parents, so she's exactly the mixed results you'd expect from mixed parents, and the "white" one really only has one definitively white trait (skin color) and not the rest; she's just an otherwise overall mixed baby with a melanin shortage. That in itself is still a pretty rare statistical occurrence, but the basic way it works is what I described above, just with more than 8 genes.

my mom and her two brothers and one sister are a good example of the same parents having kids that look completely different. i'm not sure what our ancestry is, but we have sort of a "Heinz 57" family history- there is a little bit of every flavor of European and North American genes in there somewhere.
i just like to say that we are pure white trash, with a little bit of Indian trash (is there such a thing?) thrown in for good measure.
anyways, my one uncle is the oldest- and he has a fairly dark complexion- i'd say about like the Mediterranean coast of Europe. tan, but not dark. sunlight makes him turn a darker brown, but bad sunburns are a rarity. he's also 6' tall and not skinny, but not fat- maybe 200 pounds. he has dark brown hair and has been slowly going bald since his mid 20's (he's in his late 50's now).
next, is my mom- she's a typical red head- pale white skin that turns beet red after 1/2 hour of sun exposure. not short, but not tall- 5'8 or so i think. she has the face of a native American with the high cheekbones- only pale.
next is my aunt- she has the same pale skin and basic build as my mom, but with black hair and a rounder face.
then, comes my other uncle- he looks like he walked right off the Cherokee Indian reservation. 5'9 or so with a slim build with dark skin and black hair that is as thick as it was when he was 16.
these 4 individuals all came from the same two parents over a 6 year period in the 50's, and they all look very different from each other. and their personalities are also very different, as well. each one except the youngest has worn glasses since grade school- his vision is still perfectly sharp at 53 (i think) years old.
thanks to the varied gene pool i come from, i look mostly like the first uncle i listed- but with paler skin. i've got brown hair that's disappearing over time, and a my facial hair is mostly a reddish color, but with some brown on the sides. my skin is somewhat pale with freckles, but i do tan nicely after the first good burn of the season. i'm 5'11 and weigh about 220 pounds with a somewhat solid build, where both of my brothers (who have a different father than me) are each about the same height, but weigh a good 70 pounds less and look nothing like me. they got most of their physical traits from their dad's side of the aisle- except my youngest brother, who got the same "hair falls out in the mid 20's" gene that i got. other than that, we look or act nothing alike.
yup- i'm a mutt. if i ever have kids, who knows what they will look like, since there really aren't any really dominant genes on my side of things.

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Ah, yes, I'd seen that picture before. (More and larger pictures here.) The thing is, the parents both had light and dark ancestors. In one child, genetic material from the father coding for dark skin combined with genetic material from the mother coding for dark skin, while in the other child it was the only the portion of the parents' genetic material that coded for light skin that was passed on to the daughter.

Having said this, the genetics of skin tone/colour is not yet fully understood. It's still being researched. Nevertheless, the process is clearly some kind of incomplete dominance.

P.S. How come you've only got 0 posts?! And can I welcome you to the forum before you've made any posts?

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