Is redhead dominant or recessive?

Red hair is a unique trait that only 1-2% of the global population possesses. Throughout history, redheads have faced discrimination and been associated with a fiery temper thanks to their rare genetic mutation. But what exactly causes red hair and is it a dominant or recessive trait?

In short, red hair is caused by a recessive allele on chromosome 16 that produces a mutation in the MC1R gene. This gene codes for the melanocortin 1 receptor, which is responsible for producing the pigment eumelanin that results in brown/black hair. The mutated version of MC1R produces a different pigment called pheomelanin, which results in red hair.

For an individual to have natural red hair, they must inherit two copies of the recessive red hair allele, one from each parent. A carrier of red hair will have one copy of the recessive allele and one dominant allele which codes for dark hair. Since the dominant allele takes precedence, carriers will not display red hair but can pass the recessive allele onto their children. If two carriers reproduce, there is a 25% chance of producing a redheaded child.

The Genetics Behind Red Hair

Human hair color is determined by two types of melanin pigments: eumelanin which produces brown/black hues and pheomelanin which produces red hues. The relative ratio of these two pigments determines natural hair color.

Redheads have a mutation in their melanocortin 1 receptor (MC1R) gene which regulates melanin production. The MC1R gene provides instructions for making a protein called the melanocortin 1 receptor which is present on the surface of melanocytes, specialized skin and hair cells that produce pigment.

When the MC1R gene functions normally, it binds alpha-melanocyte stimulating hormone (αMSH) which stimulates melanocytes to produce high levels of eumelanin. This results in brown or black hair.

The MC1R gene mutation associated with red hair impairs the receptor’s ability to bind αMSH. This causes melanocytes to primarily produce pheomelanin rather than eumelanin, leading to red hair color.

There are over 80 known allelic variants of the MC1R gene associated with red hair. The most common variants linked to red hair in Northern/Western Europeans are known as R151C, R160W and D294H. These are missense substitution mutations that impair αMSH binding.

How the Red Hair Alleles are Inherited

Red hair is inherited in an autosomal recessive fashion. This means an individual must inherit two copies of the recessive red hair allele, one from each parent, in order to have red hair themselves.

The red hair allele is located on chromosome 16 in the region 16q24.3. We all inherit two copies of chromosome 16, one from our mother and one from our father.

If an individual inherits the recessive red hair allele from both parents (genotype rr), they will have red hair.

If an individual only inherits one copy of the red hair allele from one parent (genotype Rr), they will be a carrier but not have red hair themselves. Their hair color will be whatever trait is dominant.

The dominant allele (R) codes for brown/black eumelanin production. So carriers have a dominant allele for eumelanin production from one parent and a recessive pheomelanin producing allele from the other. Since eumelanin production is dominant, carriers display that phenotype of darker hair while still carrying the ability to pass on red hair to their offspring.

This table summarizes the possible offspring genotypes and phenotypes when different combinations of parents with homozygous dominant (RR), heterozygous (Rr) and homozygous recessive (rr) genotypes reproduce.

As you can see, two copies of the recessive red hair allele (rr genotype) must be inherited to produce red hair. If only one copy is inherited, the individual will be a carrier but have dominant darker hair.

The only way a redheaded child can be born is if both parents carry the recessive red hair allele. If one parent is RR they cannot produce any redheaded children. Two Rr carriers have a 25% chance of producing a rr redheaded child with each pregnancy.

Prevalence of Red Hair

Only 1-2% of the global population are natural redheads. However, red hair is more common in people of Northern or Western European ancestry:

– Scotland has the highest percentage of redheads at 13% of the population
– Ireland has the second highest rate at 10%
– Less than 4% of Europeans overall have red hair
– Red hair is rare outside of Europe – less than 1% prevalence in Asia and Africa

This geographic distribution reflects the genetic origins of red hair in Paleolithic/Mesolithic hunter-gatherers that inhabited Northern Europe between 8,000 – 11,000 years ago. They migrated from the Middle East into Europe and developed lighter pigmentation to improve vitamin D production in areas with less sun exposure.

The gene for red hair arose as a mutation among these ancient Europeans and was passed on to subsequent populations across the north and west of Europe. Its frequency remains highest in those areas most populated by their ancestral hunter-gatherer descendants.

Red Hair Stereotypes

Throughout history, redheads have been associated with a fiery temper and rebellious nature. Famous redheads like Queen Elizabeth I and Napoleon Bonaparte fed the stereotype of ‘fiery reds’.

In the late 1800s the use of anesthetics was still relatively new. Doctors noticed redheads seemed to require higher doses of anesthetic gases to sedate them during surgery, fueling the perception they were somehow biologically different.

Modern research has discredited these crude stereotypes. Studies show redheads are no more prone to exhibiting a fiery temper than others. The higher anesthesia requirements are linked to specific MC1R receptor variants rather than a universal redhead trait.

While the stereotypes are unfounded, they persist in popular culture. Redheads are often portrayed as untamed and quick-tempered in books, TV and movies compared to characters with other hair colors.

Red Hair Advantages and Disadvantages

While red hair has been stigmatized, it also comes with unique health implications. Redheads tend to be more sensitive to temperature extremes and sun exposure due to their melanin deficiency. They are also more sensitive to pain and often require higher doses of anesthesia and analgesics. Here’s an overview of the pros and cons associated with red locks:

Disadvantages

– Increased sun sensitivity – lower eumelanin production makes redheads prone to sunburns and 10-100x higher risk of developing melanoma
– Temperature sensitivity – redheads are more sensitive to heat and cold due to circulation differences
– Increased pain sensitivity – redheads require higher pain medication doses, likely linked to MC1R variants
– Increased anesthesia requirements – redheads need 20% higher general anesthesia doses on average

Advantages

– Reduced risk of Parkinson’s disease – the MC1R mutation appears to be protective
– Increased vitamin D production – paler skin enables faster vitamin D synthesis from sun exposure
– Stand out from the crowd – red is a rare, striking hair color that can be seen as desirable
– Youthful appearance – red pigment fades less than darker pigments, creating a younger look

While redheads do need to take precautions against sun overexposure and skin cancer risk, most downsides are manageable. And new research is discovering health benefits like neuroprotection associated with red locks. Ultimately red hair is just an aesthetic rather than something that significantly impacts health or personality.

Famous Redheads

While only 1-2% of the population have red hair, many iconic figures throughout history and popular culture have boasted red locks:

– Historical figures like Queen Elizabeth I, Napoleon Bonaparte, Thomas Jefferson, Malcolm X, and Vladimir Lenin

– Entertainers like Lucille Ball, Conan O’Brien, Louis CK, Isla Fisher, Emma Stone, and Amy Adams

– Artists like Vincent Van Gogh, Pre-Raphaelite painters, and Gustav Klimt

– Authors like Mark Twain, Anne of Green Gables’ L.M. Montgomery, and Anne Rice

– Fictional characters like Little Orphan Annie, The Little Mermaid’s Ariel, Pippy Longstocking, Sansa and Ygritte from Game of Thrones, Poison Ivy, Mystique, Jessica Rabbit and Merida from Brave

While many express surprise that a disproportionate number of iconic figures seem to have red hair, it’s likely because the rare, striking color makes redheads stand out and be more memorable. A sampling bias causes us to recall more famous redheads compared to all the forgotten figures with common hair colors.

Nonetheless, it’s fun to imagine how history might have been different if these famous figures hadn’t possessed their red locks!

Conclusion

In summary, red hair is caused by inheriting two recessive alleles of the MC1R gene, one from each parent. This results in a switch from eumelanin to pheomelanin pigment production and red hair color.

Red hair originated as a mutation among ancient hunter-gatherers in Northern Europe tens of thousands of years ago. It remains most prevalent in people of Northern and Western European descent, especially in Scotland and Ireland where up to 13% of the population carries the trait.

The genetics behind red hair produce both disadvantages like sun/temperature sensitivity as well as possible advantages like neuroprotection. Misunderstandings around redhead biology have fueled false stereotypes about their temperaments.

While the percentages are small, red hair holds a treasured place in our cultural history and imaginations. It makes the rare iconic redheads stand out in our minds more than all those with common hair hues.

So while redheads make up a relatively rare minority group, they hold a special place in society. The genetics behind their fiery locks not only impact physical traits but also human culture and history.