By Lauren Donley
Do you know a ‘surprise’ redhead? More specifically, a red-haired offspring, originating from two non-red-haired parents? In many cases, an examination of the family tree will reveal ginger offshoots. For other families, the origin story might not be so obvious. In a nod to World Redhead Day on 26th May, let’s comb through the science of red hair and how it’s passed down from parent to child (or not).
To state the obvious, red hair isn’t very common. Only around two percent of people worldwide are born with ginger locks. Ireland has the highest concentration of redheads at around 10 percent of the population, while Scotland comes in second at roughly six percent. Due to these high numbers, it’s often assumed that red hair originated from this region. However, genetic studies have shown that it most likely arrived in northern and western Europe from Asia around 3,000 to 4,000 years ago.
Our hair colour is determined by the ratio of two different types of melanin, called eumelanin and pheomelanin. These two naturally occurring pigments are produced by specialised cells in the base of each hair follicle. These melanin pigments are then transferred into our individual hair shafts as they grow.
As a general guide, people with black or dark brown hair have mostly eumelanin, while those with blonde hair have very low levels of both eumelanin and pheomelanin. In the middle of this spectrum, our friends with red hair have mostly pheomelanin with a little eumelanin. The ratio differs from one redhead to the next, which explains the many shades, from light strawberry blonde through to dark auburn or flaming red.
According to the largest ever study on hair genetics, a single gene called melanocortin 1 receptor (MC1R) is responsible for red hair in three-quarters of people with the trait. In the remaining one-quarter, at least eight additional genes are known to be involved. Ultimately, these genes are also responsible for setting the unique blend of eumelanin and pheomelanin.
The study also showed that over 90 percent of people with red hair carry two copies of a specific variation in the MC1R gene – one copy from their mum, and one from their dad. And this is where we circle back to those surprise redheads. Along with a little bit of high school biology (Pro tip: For a helpful visual, Google ‘red hair Punnett square’).
Humans typically have 46 chromosomes in each cell: 23 from mum, and 23 from dad. In turn, each chromosome contains between 20,000 and 25,000 genes. To drill down even further, each of us has two different copies of every gene, and these are known as alleles.
For simplicity, let’s say that most redheads have two ‘ginger alleles’ in the MCR1 gene pair. If two of these redheads procreate, each parent will pass on one of their two ginger alleles. The resulting baby will also end up with two copies of the ginger allele. In the majority of cases, that baby will have red hair, like both parents.
In contrast, most non-redheads have either two ‘non-ginger alleles’ in the MCR1 gene pair, or a combination of one ginger and one non-ginger allele. In the latter scenario, these individuals are known as ‘carriers’ of the MCR1 red hair gene.
If two of these non-redheaded carriers reproduce, each parent has a 50 percent chance of passing on their only ginger allele to the baby. Overall, this equates to a 25 percent chance of spawning a baby with two ginger alleles. And hey presto, a surprise redhead is born!
For anyone nervously considering a 23andMe kit at this point, it’s important to note that the above is a simplified explanation of a very complicated genetic process. Studies have confirmed that not everyone who inherits two ginger alleles will be a redhead. And then remember those eight other genes that account for up to one-quarter of all redheads? The role of these genes is still largely unknown.
So rather than speculating any further, let’s all just raise a glass of ginger beer this World Redhead Day – to all the surprising and unsurprising redheads in our lives.
