Can two light-skinned people have a dark-skinned child?

[Mighty_Girl]

A friend and I were talking about a famous local artist who apparently has a fixation on infidelity; a lot of his songs are humorous stories about women cheating on their spouses.

One of those songs is about a couple of white - or presumably light-skinned - people who have many children, all turn out white. After some time the wife gives birth to a black child and the husband - rightly so - becomes suspicious. After years of doubting he finally musters up the courage to ask her if the black child is his, to which she responds “the black kid is the only one that’s yours”. Well, it sounds hilarious in the song.

Anyways, my friend said “well, it is funny but it is wrong, two white people can’t have a darker child, it is genetically impossible”. Well, this contradicts all I believed. He said that I could do some search about it – which I tried and came up with nothing. I am really intrigued, after years of hearing stories of white couples having dark children, something that is explained by pointing out that one of them has a dark-skinned ancestor. I always thought of that as fact.

Was I wrong all this time?

[astro]

Apparently the answer is yes.

Re: Can a childs skin color be darker than its parents?

"Desiree’s Baby”

Differences in skin color are largely due to differences in the amount of melanin, a dark pigment produced by skin cells. At least three genes control the synthesis of melanin. Each gene has two forms: an allele for high melanin production, or dark skin (A,B,C), and an allele for low melanin production, or light skin (a,b,c). Each dark skin allele (A,B,C) in the genotype adds a small but equal amount of pigment to the skin. There are seven different shades of skin color ranging from very dark (AABBCC) to very light (aabbcc). Most individuals produce a medium amount of melanin and are of intermediate skin color (AaBbCc).

The following Punnett square shows the possible offspring from a cross between two individuals of intermediate skin color.

The Heredity of Complexion

What was bothering him is this: if Puerto Ricans have been totally intermarrying (with just as many interracial couples as same-race couples) for at least six generations, why is not everyone light brown? It is true that many Puerto Ricans are light brown. But many are as fair-skinned as any Norwegian and others are as dark as any Nigerian. According to my professor, if mixing had been complete and constant since the PR census of 1850, which recorded a 50-50 Black/White population, then everyone should look blended.

Like most of us, my professor fails to remember his high-school biology. Like most of us, he has forgotten the tale of nineteenth century monk Gregor Mendel’s (1822-1884) wrinkled peas and smooth peas. Elementary genetics shows that no large intermarrying 50-50 biracial population will ever blend completely, but will continue to produce about one genetically European child in every eight and one genetically African child in every eight forever. Another way of saying this is that, although most children seem to “blend” their parents’ features, if both parents are mixed then one child in four will always be darker than both parents and one in four will always be lighter than both parents.

[CynicalGabe]

Of course it can happen, its just a fluke. The same way I bear a startling resemblence to the milkman.

[Mighty_Girl]

Well, I am trying to find out something about it and Google comes up with too much noise, but I found this site that apparently supports my friend’s belief:

http://www.multiracial.com/readers/tenzer2.html

In short the article claims that a child can never be darker than their parents. Even if one of the parents is black.

Interesting (a certain aunt of mine would have much explaining to do if my friend turns out to be right ;)).

[chrisk]

Actually, I remember hearing in high school biology that skin color in human is based about on maybe three gene pairings, each of which controls a different amount of melanin in the skin… (which is the main pigment that makes skin or hair ‘dark’,) and the two more significant of them are ‘co-dominant.’ That is, someone who has one of the genes and one of the other genes has an in-between physical characteristic (mid-brown skin.)

Don’t know how true that is, but if it is, it would tend to suggest that the sort of situation the OP is asking about would be unlikely to happen… at least, not very much darker skin than both the parents.

[Skellington]

I can’t back this up with any real evidence but for interests sake here is a story I heard not long ago:
A young english woman and her husband were living in India in the 1930s (when alot of upper crust english families would go over there for a few years). They had been ‘happily’ married 6 years and been trying for kids. She had an affair with a native and got pregnant. She know that as soon as the baby was born her husband would see what had happened and divorce her but she kept it a secret until the baby was born in the hope that maybe it was his. They went back to England. The child (a girl) was born and was white. Just as white as she and her husband. She was shocked but of corse very pleased. And they live happily ever after. Until the child got married. She married a suitable older man and 12 months later a baby boy was born - black. At this point the mother decided to tell all to save her daughter’s marrage and an interesting mystery is born.

[Colibri]

@Mighty_Girl

In short the article claims that a child can never be darker than their parents. Even if one of the parents is black.

No, this is only true if one of the parents is pure “white,” that is, has all six allelles (of the three genes mentioned by astro) of the light form. If the couple is merely “light-skinned” - actually mulatto to some degree, even if they appear white - then they can have offspring darker than either parent.

From your link:

When two mulattoes of any degree mate, each contributes both light and dark skin color genes. The child can get all or most of the dark skin color genes from both parents and be darker than either parent; the child can get all or most of the light skin color genes from both parents and be lighter than either parent; the child can get any combination of light and dark skin color genes from both parents and be whatever color that combination dictates. This principle can be illustrated in the pre-Civil War work of historian Kenneth M. Stampp. In examining manuscript census returns for 1860, he found that slave mothers who were listed as “Mulatto” often had children who were listed as “Black.” Their dark color is readily explained by laws of genetic skin color inheritance whereby two mulattoes can produce a child darker than either parent. The children referred to in the census data had mulatto mothers and either mulatto or black fathers.

Take for an example a couple that are Aabbcc and aaBbcc (where the capital letter indicates the dark form of the allele, and the alleles are codominant, that is, produce an intermeditate phenotype so that skin color is correlated with the total number of dark alleles). In this case, although they are almost pure white themselves, they can have an offspring AaBbcc, which will be darker than either parent. Similarly, parents that have genotypes AabbCa and aaBBcc will themselves be fairly light, but could produce an offspring AaBBCa, which would be much darker than either parent.

[Blake]

@Colibri

Similarly, parents that have genotypes AabbCa and aaBBcc will themselves be fairly light, but could produce an offspring AaBBCa, which would be much darker than either parent.

Nitpick.

They could produce an offspring AaBbCc or AaBbca but never AaBBCa. One allele needs to come from each parent and barring some fairly improbable crossing over events the children can’t inherit both the dominant B alleles from the same parent. Nor can they inherit both the dominant C and recessive a of the final allele form the same parent.

Doesn’t change the sense of what was said but in the interests of fighting ignorance it’s worth understanding why what you say is correct rather than just taking it on faith with a flawed understanding of genetics.

[Mighty_Girl]

Thanks, but I didn’t understand much of what you say. I can’t remember much of what I learn in biology class. Please help me translate this into a language I understand:

Scenario A: Both are really white, then it is impossible for them to have had a black child. (Duh!)

Scenario B: One of them is merely light-skinned mulatto, in which case. Could they have a dark-skinnned child?

Scenario C: Both are light-skinned mulattos. They *could *have a dark-skinned child, right?

I think my aunt is in the clear

[astro]

@Mighty_Girl

Thanks, but I didn’t understand much of what you say. I can’t remember much of what I learn in biology class. Please help me translate this into a language I understand:

Scenario A: Both are really white, then it is impossible for them to have had a black child. (Duh!)

Scenario B: One of them is merely light-skinned mulatto, in which case. Could they have a dark-skinnned child?

Scenario C: Both are light-skinned mulattos. They *could *have a dark-skinned child, right?

I think my aunt is in the clear

Both whitey white > no darker child possible
One whitey white + mulatto > no darker child possible
Light skinned mulattoos > darker child possible

And bear in mind that this hinges on the whitey white(s) also being genetically whitey white not just “looking” white.

[Colibri]

Blake is correct about the genetics in my post. Sorry about my error.

@Mighty_Girl

Thanks, but I didn’t understand much of what you say. I can’t remember much of what I learn in biology class. Please help me translate this into a language I understand:

Let’s take from the top: Everyone normally has two copies of each gene (except males for those genes on the sex chromosomes), one of which is inherited from the mother and the other from the father.

Assume that there are three genes for skin color in human, let’s call them A, B, and C.

Each of these genes has two forms, or alleles, one of which produces little melanin (let’s call it the “light” allele) and the other of which produces a lot of melanin (let’s call it the “dark” allele). Let’s indicate the dark allele with a capital letter (A,B.C), and the light allele with a small letter (a,b,c).

Unlike the main genes for eye color, these alleles do not show a dominant /recessive pattern of inheritance, in which you can have either brown eyes (which are dominant, so that it only takes one brown allele to produce brown eyes, even if the other allele is for blue), or blue eyes (which are recessive, so that you must have two blue alleles in order to produce blue eyes), but not an intermediate condition. (I am ignoring some of the complexities here that can produce hazel or green eyes.) Instead, the skin color genes show what is called co-dominance, in which those individuals with differemt alleles show an intermediate condition.

AA = dark
aa = light
Aa = medium-colored, intermediate between the two extremes

If we assume that the effects of the three different genes are additive, we end up with seven different possible degrees of skin color:

6 dark alleles (AABBCC) = darkest
5 dark (e.g. AaBBCC and other possibilities) = next darkest
4 dark (AaBbCC, etc) = slightly darker than average
3 dark (AaBbCc, etc) = intermediate between the extremes
2 dark (aaBbCc, etc) = slightly lighter than average
1 dark (aabbCc, etc) = slightly darker than the lightest
0 dark (aabbcc) = lightest

Scenario A: Both are really white, then it is impossible for them to have had a black child. (Duh!)

Right. If both are aabbcc, then there are no dark alleles present, so it’s impossible for them to have a darker child.

Scenario B: One of them is merely light-skinned mulatto, in which case. Could they have a dark-skinnned child?

If you have a pairing of an aabbcc (white) with an Aabbcc (lightest skinned mulatto), the only possible results are aabbcc (white) and Aabbcc (same color as mulatto parent). The offspring cannot be darker than the mulatto parent. This is true of any case in white one parent is aabbcc. Any dark alleles that are present must come from the mulatto parent, so that the offspring cannot be darker than the mulatto parent.

Scenario C: Both are light-skinned mulattos. They *could *have a dark-skinned child, right?

As an example, let’s take two very light skinned mulattos, both Aabbcc. There are then three possible genotypes for offspring:

aabbcc = white
Aabbcc = lightest mulatto
AAbbcc = darker mulatto, darker than either parent. This individual has obtained one dark allele from each of the parents.

Taking the example of two intermediate mulattos of genotype AaBbCc, they can produce all possible genotypes between them, including AABBCC (darkest), aabbcc (lightest) and all intermediate combinations. This is the point of the second quote in astro’s post.

I think my aunt is in the clear

Most likely, unless her kid really really does look like the milkman.

[Excalibre]

@astro

Both whitey white > no darker child possible
One whitey white + mulatto > no darker child possible
Light skinned mulattoos > darker child possible

And bear in mind that this hinges on the whitey white(s) also being genetically whitey white not just “looking” white.

So how many white people are actually light-skinned mulattos? I mean, is the European population genetically diverse enough that a significant percentage of people who believe themselves to be “white” still may have genes conferring dark skin to pass on?

[Mighty_Girl]

Interesting question Excalibre. I have heard that Southern Italians and a lot of Spaniards are not quite pure Caucasian but product of centuries of mixing. They look much darker than the average European, but I don’t know if there is any truth behind the idea.

Colibri, thanks a lot. That was quite a lesson. You’d be amazed at how ignorant I was of this. I come from a country with a large majority of mulattos and small white and black minorities. Accusations of infidelity and doubt are not uncommon, but fortunately people do believe that pretty much anyone here could have a kid that doesn’t look anything like the parents. Nice to know what the truth behind this is.

It is the first time I analyze a song under the light of science. At least the songwriter was right. And nice to know that my cousin is really my uncle’s.

[Askia]

Thanks Colibri. See, I always knew that Sir Arthur Conan Doyle got it wrong.

[Colibri]

@Excalibre

So how many white people are actually light-skinned mulattos? I mean, is the European population genetically diverse enough that a significant percentage of people who believe themselves to be “white” still may have genes conferring dark skin to pass on?

I don’t have the cite handy, but IIRC studies looking at other genes (not the ones for skin color) have shown that a majority of US blacks have some European ancestry, while a much smaller percentage of the (non-Hispanic) population that consider themselves "white’’ have some African ancestry.

I might also mention that I greatly simplified the situation with regard to skin color. There will of course not be just seven shades of coloration, but continuous variation, since 1) each of the 3 dark alleles probably produces somewhat different amounts of melanin; 2) there may be more than just two alleles present for each gene, each of which produces differing amounts of melanin; 3) precise expression of each allele may depend on yet other genes other than the main skin color ones; and 4) there may be effects of environment, such as nutrition, exposure to sunlight etc.

I would also mention that the above model may apply mainly to crosses involving European and sub-Saharan African populations. I suspect that the genetics must be different for other populations that “breed true” for intermediate skin colors. For example, American Indian populations (at least mostly pure ones) normally have a skin color that is intermediate between Europeans and Africans, yet they never produce individuals of much darker or much lighter skin color (aside from albinos or other rare variants). Therefore their genetics cannot be following the six-allele model outlined above.

[John_Mace]

@Colibri

I don’t have the cite handy, but IIRC studies looking at other genes (not the ones for skin color) have shown that a majority of US blacks have some European ancestry, while a much smaller percentage of the (non-Hispanic) population that consider themselves "white’’ have some African ancestry.

From Genes, Peoples, and Languages (p74): “Studies with genetic markers indicate an average of 30 percent of White admixture in the Black population, the frequencies varying between approximately 50 percent on average in the northern US and 10 percent in the South.”

This aritcle has some interesting statistics for White Americans, for example:

It appears that 70 percent of whites have no African ancestors. Among the 30 percent who do, the black admixture is around 2.3 percent, which would be like having about three black ancestors out of those 128.

[Mighty_Girl]

Is hair color governed by the same rules?*

Well the song also mentions they were “blonde as butter” and I want to see if I understood my friend correctly before I call him to say he was wrong.

[Colibri]

@Mighty_Girl

Is hair color governed by the same rules?*

In general, yes. Offhand, I don’t know how many genes or alleles might be involved. However, as far as I know hair color is 1) multifactorial, that is, governed by several different genes; and 2) at least some of the alleles involved are co-dominant. Therefore hair color is continuously variable (rather than occuring in discrete classes), and in many cases offspring can have hair color distinctly different than that of their parents.

@Excalibre

I mean, is the European population genetically diverse enough that a significant percentage of people who believe themselves to be “white” still may have genes conferring dark skin to pass on?

I can offer an anecdote: A friend of mine named Pedro is from Puerto Rico. He “looks” Puerto Rican - light brown skin, straight black hair, etc. Seeing him, you would have little doubt about his ancestry.

Some years ago, Pedro found out he was adopted. Out of curiosity, he investigated where his parents were from.
His birth parents were German.

[alice_in_wonderland]

Well, just to throw an anecdote in here, with little or no value other than interest:

My cousin is adopted - he is just the complexion of Tiger Woods (actually looks a lot like him).

His birth parents were both pale and white like fishbellys - hence the adoption (sad but true - oh well, my family is happy to have him). The official story is that somewhere, someone had a darker skinned relative, but I dunno.

[Obsidian]

@Colibri

Therefore hair color is continuously variable (rather than occuring in discrete classes), and in many cases offspring can have hair color distinctly different than that of their parents.

My paternal grandparents are both black-haired, olive skinned italians. All four great-grandparents were also dark-haired, and so are all of the assorted family members on both sides. My father and his sister both have bright red hair and fair skin.

We eventually found an irish last name 4 generations up grandma’s line. We have no idea where Grandpa’s red gene came from, having 100% sicillian ancestors from the same little villiage as far back as we can trace, but my father is so otherwise his spitting image that there can be no doubt this was not a milkman thing.

Dad married my blue eyed, fair skinned, light brunette mother, who’s 3/4 swedish. My sister has red hair, fair skin, hazel eyes. I have dark brown hair, dark brown eyes, olive skin. Genetics is funny.