Published on November 9th, 2020 and Updated on February 29th, 2024
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You’ll probably ask a lot of questions during your nine months of pregnancy, like how much will the baby weigh, where to put the crib, and generally how you’ll raise your little lovebug.
And of course, one of the oldest questions in the book:
Who will she resemble: you or your partner? One of the features you may wonder most about is your little one’s hair. Will she grow up with your luscious auburn locks or her father’s straight, almost jet-black mane? Or will her hair type be all her own?
It all comes down to genetics.
The Genetics of Hair
Before determining who your child will inherit his hair from, we should dive into how he’ll inherit his future mop.
There are a few essential components that determine which traits we develop—hair color or otherwise:
- Genes – Genes are the instruction booklet for your child’s attributes. Humans have between 20,000 and 25,000 genes.
- Alleles – Alleles are possible manifestations of a single gene. The combination of these distinct alleles influences which traits your child will develop. To simplify, think of each different gene as a two-piece puzzle. Mom and Dad each contribute one piece—or an allele each—to the puzzle. Which alleles Mom and Dad contribute will affect how the puzzle will turn out.
- Genotype – This is the specific DNA your child possesses, which is inherited equally from both parents. For example, your child might have brown hair genes from you, or may have blond hair genes from your partner. Those genes are his genotype.
- Phenotype – This refers to the visible traits that manifest as a result of your child’s DNA sequences. So your child’s blond hair may be one of his physical traits inherited from Father, but he may also have the genes for brown hair, thanks to Mom.
If you’re wondering what kind of hair traits your child will wind up having, the answer lies in your child’s alleles. Allele combinations are the key to your child’s phenotype. Alleles combine most often in three distinct ways:
- Homozygous – This results from two identical alleles. Homozygous traits usually manifest physically as part of your phenotype. For example, if you were wondering what color eyes will my baby have, the answer has to do with alleles. If your son inherits two brown-eyed alleles, he’ll share your eye color.
- Heterozygous – Two different alleles result in heterozygous traits, which are a bit less straightforward. With heterozygous traits, one allele may be dominant while the other is recessive. When this is the case, the dominant attribute will present physically, but the other allele will still become part of your genotype for you to pass on to future generations.
- Additive – This is the most complicated genetic variance of the three, where the frequency of multiple different alleles—the sum of all parts—create a distinct outcome. It is less black-and-white and more like a combination of many paint colors on a palette. So instead of a two-piece allele puzzle, certain alleles from various other genes are required to make up a bigger picture. This happens with human hair color, among other traits.
Where does the hair gene come from?
This question isn’t as simple as “Did you prep the baby formula?” or “Where did you leave our daughter’s shoes?” (though this has the potential to become complicated, too).
It’s not really a question of whether your child will inherit the hair gene from Mom or Dad. Instead, your child inherits a myriad of genetic factors that all add up to their very own locks.
Genetics and Hair Color
You pass by a happy family at the park or the movies and notice a brunette mom, a dark-haired dad, a blond baby, and a redhead daughter.
If hair color is genetically determined, how is this possible?
Don’t worry, this isn’t the set-up to a tricky riddle. It’s a matter of complex genetic interaction between loads of different maternal and paternal DNA sequences.
More than a hundred different genes come together to influence our hair color based on three primary factors:
- Melanin amount – Everyone’s body produces a different amount of melanin, the pigment responsible for coloring our skin and hair.
- Melanin type – There are two types of melanin, each responsible for different colors:
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- Eumelanin – This type is responsible for the spectrum of blond to black. Your dark-haired daughter will have a lot of eumelanin, while your blond baby boy has much less.
- Pheomelanin – Redheads typically have very little eumelanin but lots of pheomelanin, which takes on an orange-red color. The difference between strawberry blond and a deep red is how much pheomelanin is produced. The amount of pheomelanin produced also plays a part in answering if and when do babies get freckles?
- Melanin distribution – How closely packed the pigment granules are affects how deep the color will be. Densely packed melanin leads to richer colors than sparse pigments.
Eumelanin and pheomelanin genes are additive—not homozygous or heterozygous. That means it requires many genetic factors to align to manifest in a child’s phenotype. Some genes are activated (“on”) while others are not (“off”). The more activated eumelanin genes there are, the darker the hair color. The more activated pheomelanin genes, the more intense the red hair color.
It kind of works like mixing paint colors on a palette.
Let’s say that 1 represents an “on” eumelanin gene, while 0 corresponds to an “off” gene. Think of 1 as a darker paint color like dark brown or black, while 0 signifies a much lighter paint color, like white. The more 1 you have in the mix—or activated gene—the darker the color will be. The more 0—or inactive gene—you have, the lighter the final pigment will be.
Now imagine mom and dad have nearly identical hair colors: let’s say a medium brown. The composition of their hair color genetics is probably the same: 11110000—half on, half off.
Their son receives half of each parent’s DNA in some random combination. Maybe he gets 1111 from mom and 1100 from dad, resulting in 11111100. He’ll have darker hair than his parents because of the increased amount of activated pigment genes. But his younger sister grows up with blonder hair than anyone in their family. Maybe she only got one activated gene, and the rest were turned off.
Whatever the final color, your child’s locks will be a work of genetic art.
Genetics and Hair Texture
Not only is hair texture a combination of tons of varied genes, just like hair color, but there are also different genes responsible for curly or straight hair across different cultures.
Your best friend from Nigeria and your great aunt from Spain might both have curly hair, but the reason why is largely different, even if their curl patterns look identical.
Hair texture is also an example of a genetic phenomenon called incomplete dominance—and not the kind in Animal Planet documentaries.
Typically, when you inherit one dominant allele and another recessive allele, the dominant one will dictate the phenotypic trait while the recessive trait never materializes. With incomplete dominance, the dominant gene variant won’t just take over. Each allele is an equal partner in the equation. This is why there’s such variation between human hair types and textures, rather than just straight or curly.
So how will your kiddo’s hair manifest in real life, based on you and your partner’s own hair textures? There’s no standard answer without a closer look at their genotype, but here’s a breakdown of the expected potential outcomes:
- Both parents at the same end of the extreme – If you and your partner both have, let’s say, very curly hair, then you each have mostly curly genes to pass on. Your daughter would most likely share your curls because she would inherit very few, if any, straight-haired genes.
- One parent at one extreme, the other at the opposite – When mom has stick-straight hair and dad has a wild, curly mop, your son is likely to grow up somewhere in between: with a wavy head of hair. Mom passes down all (or mostly) straight genes, and dad does the same with his curly genes—your son, therefore, has an even split.
- Both parents somewhere in the middle – This middle-ground will create the widest variation in your kid’s hair type. If you and your partner both have medium wavy hair, you each have about half curly genes and half straight genes. You’ll both pass down some random combination of these genes to your offspring. So you might pass down an even split of straight and curly, but your partner could bestow your daughter with 85% curly genes—in this case, she’d have curlier hair than either you or her father.
This representation is a bit oversimplified because all hair texture genes aren’t alike.
For example, one gene impacts the trichohyalin (TCHH) in your hair follicles. TCHH is a protein found in the hair’s shaft that helps create an anchor for the hair fiber, tightening the curls toward the hair follicle. This one gene accounts for about 6% of the variation in your hair texture, which is more than any other single gene (that we know of, anyway).
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This post has been reviewed for accuracy by the following medical professional:
Dr. Heather Soper, Certified Nurse Midwife
Dr. Heather Soper brings over 15 years of experience in women's health and obstetrics to her role as the owner of The Genesis Resort for Birth. Complementing her clinical practice, she serves as an Assistant Professor of Nursing at James Madison University, where she educates nursing students with a focus on compassionate, patient-centered care. Her advanced training and dedication to midwifery are evident in her contribution to both academia and the wellness of expectant mothers
Sources:
- 23andMe. Hair Color & Genetics. https://www.23andme.com/topics/traits/hair-color/
- U.S. National Library of Medicine. Is hair color determined by genetics? https://ghr.nlm.nih.gov/primer/traits/haircolor
- Cellular Research Institute Genetics. Do You Get Your Hair Genes From Mom Or Dad? https://www.crigenetics.com/blog/do-you-get-your-hair-genes-from-mom-or-dad
- The American Journal of Human Genetics. Common Variants in the Trichohyalin Gene Are Associated with Straight Hair in Europeans. https://www.cell.com/ajhg/fulltext/S0002-9297(09)00464-9
- Nature Genetics. Susceptibility variants for male-pattern baldness on chromosome 20p11. https://www.nature.com/articles/ng.228
- Science Daily. Tendency To Hair Loss Inherited From Mother. https://www.sciencedaily.com/releases/2005/05/050520172151.htm
- U.S. National Library of Medicine. Is hair texture determined by genetics? https://ghr.nlm.nih.gov/primer/traits/hairtexture
- Stanford at The Tech. Ask A Geneticist: Other Genetic Principles. https://genetics.thetech.org/ask-a-geneticist/three-equally-represented-phenotypes
- Healthline. What Does It Mean to Be Homozygous? https://www.healthline.com/health/homozygous
- Stanford at The Tech. Ask A Geneticist: Other Traits. https://genetics.thetech.org/ask/ask45
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SneakPeek aims to provide the most accurate and up-to-date information to help our readers make informed decisions regarding their health before, during, and after pregnancy. This article was written based upon trusted scientific research studies and/or articles. Credible information sources for this article are cited and hyperlinked.
