Is Curly Hair Recessive Or Dominant Trait?


Have you ever looked at someone’s curly hair and wondered why their locks spiral while others have straight hair? The answer lies in hair genetics. Genes shape the way our hair grows, its texture, its color, and even the changes it undergoes in different situations.

Curly hair, in particular, has sparked interest. Is curly hair a dominant trait or a recessive one? How do genes for curly hair and straight hair interact? And is curly hair rare? These are some of the curly hair questions we’ll dive into.

We’ll explore why curly hair has evolved differently across various regions and cultures.

Let’s discover the intricate beauty and diversity that our genes bring to our hair.

Quick Note:

In a rush? Here’s the gist: The shape, texture, and color of our hair, including the unique patterns of curls, are shaped by a mix of genetic instructions and external factors.

Genetically, curly hair often follows a dominant pattern, meaning if you inherit the curly hair gene from even one parent, you’re more likely to have curls. Or if your parent has curls, you have a high chance of getting it. The science delves into the roles of specific genes, like TCHH and KRTAP6-1, which contribute to hair texture. Yet, having these genes doesn’t rigidly set your hair type.

Environmental factors, like humidity and climate, along with personal choices like hair care practices, greatly affect hair texture and health. For example, humidity can intensify curls, while certain hair treatments can temporarily alter hair texture.

Curious about more details on the genetic and environmental shapes our hair? Keep reading for an in-depth exploration.

Basics of Hair Biology

Hair grows from hair follicles, which are located in the dermis, the middle layer of the skin. These follicles are all over our skin except on our palms and soles. They’re hooked up to blood vessels and nerves and make hair fibers from a protein called keratin. The same protein that is also found in nails, horns, and feathers.

Hair growth happens in cycles, consisting of three main phases.

First, there’s the anagen phase, where hair actively grows. Next, the catagen phase is like a transition period where the hair stops growing and prepares to rest. Finally, the telogen phase is when the hair takes a break and eventually falls out, making room for new hair.

curly hair genetics

In general, we mainly describe hair in two categories, straight and curly. But there is a variety of curly hair depending on the degree of curls.

Types of Hair Curls

  1. Type 1: Straight Hair
    • Type 1A: Very straight and fine, often difficult to hold a curl.
    • Type 1B: Mostly straight but with a slight bend.
    • Type 1C: Straight with some waves and a bit more body.
  2. Type 2: Wavy Hair
    • Type 2A: Slightly wavy with a loose, tousled texture.
    • Type 2B: Medium waves, more defined and can start to form ‘S’ shapes.
    • Type 2C: Wavier with thicker waves and a tendency to frizz.
  3. Type 3: Curly Hair
    • Type 3A: Loose curls with a defined ‘S’ pattern.
    • Type 3B: Medium to tight curls that maintain the ‘S’ pattern.
    • Type 3C: Tight curls or coils that are densely packed together.
  4. Type 4: Coily Hair
    • Type 4A: Soft, fine, tightly coiled hair forming an ‘S’ pattern.
    • Type 4B: Z-shaped coils with a more cotton-like feel.
    • Type 4C: Coils that are so tightly kinked, there is no defined curl pattern.

Factors That Influence Curliness

  • Follicle Shape and Size: Round follicles usually produce straight hair, while oval or elliptical follicles tend to create curly or coily hair.
  • Keratin Distribution: The way keratin is distributed along the hair shaft affects its curliness.
  • Genetics: Curly hair genetics come into play here too. Whether curly hair is dominant or recessive, and how curly hair genes interact with each other, can affect your hair’s texture.

Understanding these things can help explain the diversity in hair types across different people and families. So, while it might seem simple, there’s a lot happening beneath the surface that gives you your unique hair!

Genetics of Curly Hair

Understanding the genetics of curly hair involves exploring how this trait is passed down through generations and the interaction of various genes that influence hair texture.

Curly hair, a trait many people either have or desire, is deeply rooted in our genetic makeup.

The Genetic Basis of Curly Hair

Mendelian Genetics and Hair Texture: Mendel’s experiments with plants showed that some traits are dominant, meaning they are more likely to appear in offspring, while others are recessive, or less likely to appear.

In hair texture, this principle is evident where curly hair often follows a dominant pattern, meaning if you inherit the curly hair gene from even one parent, you are likely to have curly hair.

Each of us inherits two versions (alleles) of every gene, one from each parent. When one allele is dominant over the other, it’s like having a louder voice in a conversation; it expresses itself even in the presence of another allele. This dominant allele masks the effect of the other, which is termed as recessive.

On the other hand, a recessive allele can only show its characteristics when it’s paired with another recessive allele. Think of it like a quiet voice that’s only heard when there are no louder voices around. In essence, the recessive trait becomes visible only in the absence of the dominant allele.

curly hair inheritance

Key Genes Influencing Hair Texture:

  • The TCHH Gene plays a significant role in determining hair texture. Variants of this gene contribute to curliness, and having certain variants can result in a dominant curly hair phenotype.
  • The Keratin-Associated Protein (KAP) Genes are crucial in deciding hair texture. Variants in genes like KRTAP6-1, associated with straight hair, showcase a recessive pattern, necessitating two copies for the straight hair phenotype.

Gene Interaction and Complexity

The genetics of hair texture isn’t determined by a single gene. It’s an additive trait, meaning multiple genes contribute to the final texture. This interaction results in the diverse range of hair types observed.

There are even some rare hair conditions that are caused by specific genetic changes, like monilethrix, which makes hair brittle, and uncombable hair syndrome, which makes hair dry and hard to manage.

Environmental factors, hormonal changes, and hair care practices also interact with these genes, influencing hair texture.

Inheritance Pattern of Curly Hair

Is Curly Hair Dominant or Recessive Trait

When it comes to determining whether curly or straight hair is genetically dominant, the answer is clear: curly hair is the dominant trait. This means that if a child inherits the gene for curly hair from just one parent, the child is likely to have curly hair.

On the other hand, straight hair is caused by recessive alleles, meaning that an individual must receive the straight hair gene from both parents for the trait to be expressed.

In essence, a single gene for curly hair from one parent is enough to result in curly hair, whereas straight hair only appears when the recessive gene is passed down by both parents.

Inheritance Scenarios:

  • If one parent has curly hair (dominant allele) and the other has straight hair but carries a recessive curly hair allele (heterozygous), the child has a 50% chance of having curly hair. If the curly hair parent genotype is homozygous meaning both alleles code for curliness than the chance of having a curly hair kid is almost 100%.
  • If both parents have curly hair, their children are more likely to inherit curly hair.

The field of hair genetics is always growing, with new discoveries being made all the time. For instance, a study from Australia found 10 new genes linked to curly hair in people of European descent.

This study showed us that hair texture is influenced by a mix of different genetic factors, some having a stronger impact than others.

Understanding the genetics of curly hair and straight hair not only highlights the intricacies of genetic transmission but also celebrates the diversity of hair types across individuals and families.

Extra Reading: Genetics of hair loss!

Is Curly Hair Rare?

Yes, curly hair is relatively rare. Globally, less than 15% of the population has naturally curly hair, making it a unique trait among humans. This rarity is due to the specific genetic combinations required to produce the curly hair texture.

Additionally, cultural and personal preferences often lead to many individuals with natural curls straightening their hair, further diminishing its visibility in the general population.

Embracing natural curls not only highlights this rarity but also celebrates the diverse beauty standards that exist across cultures. Curly hair, with its distinct spiral and wave patterns, offers a unique aesthetic appeal and stands out in a crowd, making it a striking feature for those who choose to wear their hair naturally.

Environmental and Lifestyle Factors Influencing Hair Texture

Not only do our genes play a role in whether we have curly or straight hair, but our surroundings and how we live our lives can also have a big impact on our hair texture. Here’s how:

  • Humidity and Climate: Ever noticed how your hair gets frizzy on a humid day? That’s because the amount of water in the air, or humidity, can make your hair change shape. Remember that Monica’s hair episode on Friends? High humidity often makes hair curlier or puffier, while low humidity might make it flatter or drier. The climate where you live can also affect your hair. Too much sun, wind, or cold can damage your hair, causing it to break more easily or look less shiny.
  • Hormones, Aging, and Medical Treatments: Our bodies produce chemicals called hormones, which can change our hair texture. Changes in hormones during times like puberty, pregnancy, or menopause can make hair thicker or shinier. As we get older, our hair can become thinner and drier, and some medical treatments like chemotherapy can also change how our hair looks and feels.
  • Hair Care Practices: The way we take care of our hair is super important. Everything from washing and drying to styling and dyeing can change our hair’s texture. For example, using certain shampoos and conditioners can add moisture, while styling tools like hairdryers or straighteners can apply heat. It’s important to use these products and tools carefully to keep our hair healthy.
curly hair problems

So, if you’re wondering why your hair acts a certain way in different weather, or why it’s changed over time, it might be down to these environmental and lifestyle factors.

By understanding them, you can figure out the best ways to take care of your hair, whether it’s curly, straight, or somewhere in between.

Evolutionary Perspective on Hair Types

When we look at different hair types, like curly hair or straight hair, we’re actually looking at a story that’s been shaped by our history and environment. Here’s a simple way to understand some of the ideas about how our hair came to be the way it is:

  • The Thermoregulation Hypothesis: This idea says that our hair type evolved based on where our ancestors lived and the climate there. Curly hair might have started in hot, humid places like sub-Saharan Africa. It’s thought that curly hair helped protect against the sun and kept people cool by reducing the need to sweat. This could have been really important for keeping hydrated and cool. Straight hair, on the other hand, might have developed in colder, drier areas like northern Eurasia, helping to keep people warm by trapping heat.
  • The Sexual Selection Hypothesis: This theory suggests that hair types evolved because of what people found attractive. Curly hair might have been seen as a sign of good health and beauty, making someone more appealing as a partner. Straight hair, in some cultures, might have been linked to looking youthful or having a certain social status.
  • The Drift and Migration Hypothesis: This one’s about random changes in our genes and how people move around the globe. It suggests that curly hair is the original hair type of humans, and straight hair comes from changes in our genes. These changes might have been just by chance, or maybe due to things like the environment or diet. As people moved to new places, they took these new hair types with them.
curly hair gene

All these ideas show us how complex and interesting the story of our hair is. It’s not just about curly hair being dominant or recessive, or whether curly hair is rare. It’s about how our hair tells the story of where we’ve come from and the environments we’ve adapted to.

There could be other reasons too, like natural selection or cultural factors, that have shaped the way our hair looks today.

Curly Hair Across Different Populations

When we talk about curly hair, it’s fascinating to see how it appears in various populations around the world.

Curly hair isn’t limited to just one group of people; it’s a global trait showing the rich diversity and complexity of human genetics.

Let’s look at how curly hair varies in different parts of the world:

curly hair across populations

Curly Hair in African Populations

In many African populations, particularly those from sub-Saharan regions, curly hair is quite common. It often has tight coils forming “S” or “Z” shapes and can be either fine or thick. African curly hair is known for its ability to maintain complex hairstyles and is celebrated for its versatility.

The curly hair in these populations is largely influenced by the TCHH gene, which helps in shaping the hair. This gene has a version, called the rs11803731 G allele, that’s linked to curly hair and is quite common in African groups. This particular version is dominant, meaning having just one copy can give you curly hair, and having two can make your hair even curlier.

Another gene, the EDAR gene, plays a role in the development of hair follicles and the production of hair fibers. A variant of this gene, known as the rs3827760 G allele, is associated with thicker and coarser hair and is found in some African populations.

Curly Hair in European Populations

Curly hair is also present in European populations, especially in areas with a mix of genetic backgrounds like the Mediterranean, the British Isles, and Scandinavia. Here, hair textures range from loose waves to tight curls.

In Europeans, curly hair is influenced by several genes. For instance, the KRTAP6-1 gene, associated with keratin in hair fibers, has a variant linked to straight hair. This variant, the rs17646946 C allele, is recessive, meaning you need two copies for straight hair. Even one copy of this variant can reduce hair curliness.

Another gene, PRSS53, is involved in hair fiber formation and shape determination. A variant of this gene, the rs554219 C allele, is linked to curly hair and is more prevalent in Europeans, particularly those of Celtic origin.

Curly Hair in Asian and Middle Eastern Populations

While straight hair is more typical in many Asian and Middle Eastern populations, regions in South Asia, Central Asia, and the Middle East have individuals with naturally curly hair. This reflects the genetic diversity in these areas.

The same genes affecting curly hair in other populations, like TCHH, EDAR, KRTAP6-1, and PRSS53, also influence hair in Asian and Middle Eastern groups. However, the prevalence and distribution of these genes and their variants can vary.

For example, the EDAR gene variant linked to thicker hair is common in East Asians, while the PRSS53 gene variant associated with curly hair is found in some South Asian and Middle Eastern populations.

In summary, the prevalence of curly hair in different populations and regions is complex and ongoing, reflecting human diversity and adaptability.

It’s not just about whether curly hair is dominant or recessive; it’s about understanding the intricate interplay of genetics, natural selection, and cultural factors that shape our hair.

Debunking Common Myths About Curly Hair

Curly hair is often surrounded by a lot of myths and misconceptions. Let’s clear up some of these and shed light on the facts about curly hair:

Myth: Curly Hair is Unprofessional and Messy

There’s a long-standing myth that curly hair is seen as less professional or more disorderly, especially among people of color. This idea might come from historical and cultural biases where curly hair has been viewed negatively.

The truth is, curly hair is just as professional and neat as any other hair type. It’s a natural part of someone’s identity and can be styled in many ways to fit different occasions and preferences. Curly hair is not a sign of disorder; it’s a unique trait that can be a source of pride and empowerment.

embrace curly hair

Myth: Curly Hair Doesn’t Need Frequent Washing

It’s a common belief that curly hair doesn’t get as dirty or oily as straight hair, leading many to avoid regular washing. The fear is that frequent washing might strip away natural oils, leading to frizz and dullness.

Curly hair does need to be washed regularly, but the frequency depends on various factors like scalp condition and hair porosity. While over-washing can dry out curly hair, not washing enough can lead to scalp problems and buildup. The key is to find a gentle, moisturizing routine that works for you.

Myth: Curly Hair Can be Permanently Straightened

Many believe that treatments like relaxers, keratin treatments, or Brazilian blowouts can permanently turn curly hair straight. This myth is fueled by the wide availability of these treatments.

The fact is that curly hair can only be temporarily altered. Curly hair’s texture is determined by genetics and the structure of hair follicles, which can’t be permanently altered by external treatments. While certain treatments can temporarily straighten hair, they’re not permanent solutions and can sometimes cause damage.

Final Words About Genetics Of Curly Hair

The genetic role in determining curly hair is both fascinating and complex. The interplay of genes such as TCHH, EDAR, KRTAP6-1, and PRSS53, and their interactions with environmental factors, shows the intricate biology that leads to the diversity of hair textures we see across populations.

From the dominant and recessive dynamics of hair genes to the influence of evolutionary factors and cultural perceptions, curly hair genetics represents a unique aspect of human diversity.

Acknowledging the need for proper care and understanding empowers individuals with curly hair to embrace their natural beauty confidently.


Leave a Comment

Your email address will not be published. Required fields are marked *