Expert: Dana Krempels, Ph.D. - 4/10/2008

Question
Hi Dana,  I am 7 months pregnant and am (as all expectant mothers are) very excited about how my baby will look...in particular, I am very interested to hear your opinion on hair colour.

I am a natural red head with green eyes and my husband has mousey brown hair and has blue eyes.  We both have fair skin (me in particular and I have freckles on my face and arms).

My father is olive skinned with brown eyes and black hair and my mother has mid brown hair with greeny grey eyes (she also has freckles but more than me).  My brother is olive skinned and has greeny grey eyes with dark brown hair.

On my husband's side...his mother has black hair with olive skin and his father has mousey brown hair with blue eyes. My husband's sister has the exact same colouring as he does (mousey brown, blondey hair with blue eyes).

Both sets of our grandparent's were mid toned skin with light brown and dark hair. None of them were read heads- so there must have been a red head somewhere further back?On my father's side of the family, most relatives were dark and have jewish/ hebrew roots.

I would be so grateful if you could inform me of whether you think my baby will have red hair like me?  Or whether babies tend to take after the father's side of the family in terms of hair and eyes.

I have heard so many different explanations on this that it has just all become a little confusing now!  From a scientific point of view, I find it very interesting that I am the only red head in the family tree...and am intriguied to find out whether I would be likely to pass this on to my baby.

thank you so much for your time as I am sure you have so many questions like this, seeing as you specialise in genetics!

many thanks again and I really look forward to your response,

simona

Answer
Dear Simona,

Human hair, eye, and skin color are very complex and difficult to predict, because each of these traits is controlled by more than one gene.  It's not really a matter of a child taking after the father or mother's side.  Genes don't work that way.  What matters is which parent has the dominant versions of the various genes that affect the traits in question, because these are the ones most likely to be expressed by the child--though not always.

Every human carries two copies of every gene.  Scientists now estimate that a human has about 30,000 genes in the genome, and every human has two copies of that genome:  one from mom, and one from dad.  The two versions of each gene (called *alleles) may be the same in a single person, or they may be different.

A brief example.  Let's say that there's a human gene that codes for the shape of the forehead hairline.  There are two versions of the gene.  One, which we'll call "W" codes for a small "V" of hair to point down onto the forehead (Widow's Peak).  The other version, which we'll call "w", codes for a straight hairline.  In this case, the W allele of the gene masks the expression of the w allele.  The W is dominant, and the w is recessive.  So if every person has two copies of this gene, then the possible combinations are:

WW - Widow's peak
Ww - Widow's peak
ww - straight

Human hair, skin and eye color are not that simple.  Instead of being controlled by only one gene, these traits are each controlled by *several* different genes, each with two or more versions (alleles).
This means that the different versions can combine in unpredictable ways to produce a wide range of phenotypes (physical appearance).

A trait that is controlled by several genes is called a POLYGENIC TRAIT. A polygenic trait is the expression of a single phenotypic trait that is affected by the action of more than one gene.

There are too many examples to list, since most traits are, at least to some degree, polygenic.  But human hair color, eye color, and skin color are among them.

One cute, easy-to-see example of a polygenic trait is the inheritance of fruit color in bell peppers, and it is a bit analogous to the human traits just named. There are at least three genes involved here, which we'll abbreviate as:

   * Y - timing of chlorophyll elimination (Y - early; y - normal)
   * R - color of carotenoids (R - red; r - yellow)
   * C - regulation of carotenoid deposition
    (C - normal; c1, c2 - lowered concentration)

(The capital letters indicate the dominant alleles; the lower case indicate various versions of recessive alleles.)

This leads to a few possible genotypes producing interesting phenotypes:
         o Y- rr c1c2 - pale yellow
         o Y- rr Cc2 - darker yellow
         o yy rr CC - green
         o Y- R- CC - red
         o yy Rr CC - purple
         o Y- Rr Cc2 - pale yellow

You can see what these look like here:

http://www.bio.miami.edu/dana/pix/bellpeppers.jpg

See?  It is a little bit like human color, but in this case there are only *three* genes involved.  Imagine how complicated things get when there are more than three genes, as there are in human hair, eye, and skin color!

The more genes involved in the expression/appearance of a trait, the more possible variations there are, and the more impossible it becomes to guess what a baby will look like, especially if you don't know the exact genetics of the parents.  (Knowing the grandparents' phenotypes can help, but usually not very much.)

Hair color is a result of interaction between several genes that not only control the *color* of the hair pigmentation (brown eumelanin pigment or red phaeomelanin pigment), but also *how much* pigment is deposited in the hair shaft.  The darker the hair, the greater the melanin deposition, but one can't really predict how dark a baby's hair will be, since s/he may inherit a wide variety of "darkness level" genes from both parents, and they can recombine in various ways.

That said, red hair is usually recessive to the other hair colors.  Unless your husband has red hair in his family tree, it's more likely that your baby will have, at best, reddish-brown hair, but not bright red.  Again, it's nearly impossible to predict what the combination of genes in your baby will produce, and hair color can also *change* with age!

Similarly, light colored eyes (blue, green, hazel, grey, etc.) are usually considered recessive to dark-colored eyes.  But this trait, too, is controlled by at least five different genes.  Because both you and your husband have light-colored eyes, it's extremely unlikely that your child will have brown eyes.  But there's no way to know in advance whether they'll be green or blue.  The chances are probably about 50/50 either way.

Skin color is probably the most complex of all the traits.  Freckles are apparently controlled by only one gene, and freckles are considered dominant to non-freckles.  But various factors during development can affect this, and exposure to sunlight can also determine the level of freckling that is expressed.

The shade of the skin in humans may be controlled by several genes, each with several alleles, and this makes the prediction of skin tone in a baby a nearly impossible task.

I know this doesn't give you the answer you were seeking, but I hope it at least gives you an idea of how truly complicated (if not impossible) it is to predict something like this.  My educated guess would be that your baby will have reddish-brown hair with green or blue eyes.  But as you can see from all of the above, that is just what it is:  an educated (if somewhat wild) guess.

Whatever color the baby, I hope s/he will be happy and healthy!  Good luck!

Dana