What Color Hair Will My Baby Have? A Genetic Explanation
What will your baby look like? Hair color and eye color are the most common things expecting parents wonder about. While there is no sure bet, you can make some good guesses with the right information.
To understand how hair color works, you will need to understand some basic genetics. During my time studying genetics at the University of California, Santa Cruz and teaching genetics in the San Francisco Unified School District, I have learned a great deal about genetic compositions and make-up can have an impact. Your genetic code consists of tens of thousands of directions that tell your body how to grow, called genes. Genes are stored inside chromosomes and determine everything from your blood type to your biological sex to your hair color.
For every gene, you have two alleles. One came from your mother and one from your father. Both alleles are stored in your chromosomes, but if they are different, only one shows up in your appearance.
For example, if you have one blue-eyed allele and one brown-eyed allele, you will have brown eyes. That is because the brown-eyed allele is dominant over the blue-eyed allele. Generally, darker colors are dominant over lighter colors. The non-dominant alleles are called recessive, and they only present when a person has two of them.
The gene code that you carry is called your genotype. The traits that you actually present are your phenotype. Parts of the genotype that do not show up in your appearance can still be passed along to your children.
How Genetics Affects Hair Color
Let’s apply this logic to hair color. We will use brown and blonde hair in our example and later discuss other common hair colors.
Brown hair is dominant over blonde hair. Children with two brown-haired alleles will present brown hair. Children with one brown-haired allele and one blonde-haired allele will present brown hair as well. Only those with two blonde-haired alleles will have blonde hair.
Now let’s take a look at how we can use genetics to guess your baby’s hair color. If you remember Punnet Squares from your biology classes in school, that is where we are going with this.
Two Blonde Parents Make a Blonde Baby
If both parents are blonde, they will certainly have a blonde child. Here, we know that both parents’ genotypes contain only blonde traits because that is the only way they could have blonde hair. A brown allele would have dominated, resulting in brown hair. If both parents carry only blonde alleles, they can only pass on blonde alleles, therefore, their child must be blonde.
Brunettes Can Give Birth To Blondes
If one parent is blonde and the other brunette, they might have a blonde child. This can only happen if the brunette parent carries the blonde allele. If he carries only brown alleles, he can only pass on brown alleles, and they’ll dominate causing his child to have brown hair.
Looking back at the grandparents (the brunette’s parents), if one is blonde, he surely carries the trait. If both are brunette, however, it is still possible that one or both carry the blonde allele and could have passed it on.
A baby born from a blonde/brunette pair where the brunette carries the recessive blonde trait has a 50/50 chance between the two colors. However, if the brunette does not carry the recessive blonde trait, the baby will have brown hair.
If both parents are brunette, they can only have a blonde child if they both carry the recessive blonde trait. But even if they do, the chance of giving birth to a blonde is just one in four.
What about Redheads?
One to two percent of humans have red or orange hair. The allele for red hair is neither dominant nor recessive. Red hair is an incomplete dominant. When a baby receives an allele for red hair, it will blend with its accompanying allele. A red-blonde genotype presents as strawberry blonde and a red-brown genotype presents as auburn.
What about Black Hair?
Black hair is the most common hair color worldwide. Black hair is made from a subtype of the same pigment that makes brown and blonde. It is a dominant trait and less likely to blend with lighter pigments than brown hair. In other words, it’s more likely for a baby born to a brown-blonde pair to end up with light brown or dark blonde hair. But if one parent has black hair, it is more common to see a jet black-haired baby.
Shades and Pigmentation
In truth, the genetics of hair color is just a little more complicated than your basic biology class might claim. Hair gets its color from pigment, and the amount of pigment in the hair affects its exact shade. So we are not really looking at completely separate hair color genes, but rather differing amounts of the same kind of pigment: melanin.
Not only that but the amount of melanin present changes throughout life. A single person may have different color hair at different ages.
Two types of pigment give hair its color: eumelanin and pheomelanin.
Eumelanin makes hair brown or black, and the amount of eumelanin present determines how dark the hair is. Smaller amounts of eumelanin make a person’s hair blonde, while larger concentrations make it brown. A subtype of eumelanin makes hair black (interestingly, smaller concentrations of this subtype results in white hair).
Pheomelanin causes hair to look red or orange. All humans have some pheomelanin in their hair, but true redheads have little to no eumelanin. Mixes of eumelanin and pheomelanin lead to auburn or strawberry blonde hair.
Human hair color comes in a variety of shades depending on the particular mix and concentration of pigments. The Fischer-Saller scale, used in physical anthropology and medicine, identifies a variety of shades on the spectrum between light and dark, red and brown.
The categories identified on the Fischer-Saller scale range from very light (A-E), through light (F-L), light brown (M-O), brown (P-T), and finally to brown-black and black (U-Y).
A separate range specifies red and red-blonde (I-VI). The scale also identifies black, gray from age, white from age, and white from albinism.
Albinism is a condition in which an individual carries no pigmentation, or very little. Without any melanin, there is no color, so someone with albinism will have white or very light blonde hair. Some types of albinism affect only certain areas of the body, but most affect the hair, skin, and eyes.
Albinism is rare and passed genetically. It is a recessive trait, so both parents would need to carry the allele for it to present. Hair is not a problem so much as skin, which can burn easily without any pigmentation to protect it.
Hair Color Changes Throughout Life
Hair color is not set for life. A baby born with dark hair may change to having light brown on blonde hair during the first six months. Even then, babies and toddlers with blonde or red hair often develop brown hair as they age. It may darken slowly during early childhood, or it may change more abruptly during adolescence due to hormonal changes. From mid-infanthood on through childhood, the most common changes in hair color are caused by increased concentrations of eumelanin.
Later in life, melanin stops being produced and hair turns grey and white. The age at which graying starts is determined by a combination of genetics and environmental factors.
It Gets Even More Complicated
As mentioned, the concentrations of two pigments determine the hair’s exact shade. But there is so much more to it, and science has not even fully caught up. Zooming in on granules of pigment in human hair, biologists have discovered that they can be fine, coarse, or obscure, and they may appear streaked or clumped. Their density varied on different areas of the same person’s hair, with no apparent order or pattern. And beyond pigment concentration, the exact shade presented depended on many factors, including transparency and reflectivity.
So, can you predict what color your baby’s hair will be? You can definitely make an educated guess. Some couples will be able to rule out certain colors (for the most part), while others can be sure there’s a chance for more than one result. Nevertheless, hair color can change over time. Whether you give birth to a strawberry blonde or brown-black haired baby, you cannot be sure he will stay that way!
Now that you have an idea of what color hair baby will have, you might be curious about eye color? Find out what color eyes your baby will have based on genetics.