Quick Answer
No, mixing black hair and blonde hair genes will not make red hair. Red hair is caused by a specific gene mutation that results in the production of a reddish pigment called pheomelanin. For red hair to occur, both parents must carry and pass on a copy of the red hair gene variant. If one parent has black hair and the other has blonde, their hair colors are caused by different pigments (eumelanin and pheomelanin respectively) and they do not carry the gene for red hair. The only way they could have a redheaded child is if both were secretly carrying a recessive copy of the red hair gene from distant ancestors.
Genetics of Hair Color
Human hair color is determined by the type and amount of melanin pigment produced in hair follicles. There are two main types of melanin:
- Eumelanin – Brown and black pigment
- Pheomelanin – Red and yellow pigment
Hair color depends on the ratio of eumelanin to pheomelanin. Higher levels of eumelanin result in brown or black hair, while higher levels of pheomelanin result in blonde or red hair.
Several different genes influence melanin production and lead to varying hair colors:
- MC1R – A major gene that controls the type of melanin. Variants in MC1R cause red hair.
- OCA2 – Influences brown/black eumelanin production.
- SLC24A4 – Influences blonde pheomelanin production.
Eumelanin and Black Hair
The pigment eumelanin produces black and brown shades of hair color. The genes OCA2 and MC1R regulate eumelanin synthesis.
The OCA2 gene encodes the P protein which is essential for eumelanin production. Certain variations in OCA2 lead to reduced P protein activity and result in less brown/black pigment.
The MC1R gene encodes the melanocortin 1 receptor, which binds to melanocyte-stimulating hormone (MSH). This stimulates eumelanin production. Variants in MC1R can disrupt eumelanin synthesis.
Individuals with two copies of the dominant versions of OCA2 and MC1R will produce high levels of eumelanin, leading to black hair.
Pheomelanin and Blonde Hair
The pigment pheomelanin produces blonde and red hair shades. The genes MC1R and SLC24A4 regulate pheomelanin levels.
The SLC24A4 gene encodes a protein that helps produce pheomelanin. Certain variants lead to more pheomelanin production and lighter blonde hair.
Meanwhile, MC1R variants can impair eumelanin synthesis and cause more pheomelanin production. Individuals with two copies of the recessive MC1R red hair gene have bright red hair.
Those with one copy of the red hair MC1R variant combined with variants in OCA2 or SLC24A4 can have strawberry blonde or auburn hair.
Red Hair Genetics
Red hair is a recessive trait that must be inherited from both parents. It only occurs when two MC1R red hair variants are present.
For a child to have red hair, both parents must be carriers of the MC1R red hair mutation, meaning they both have one copy of the variant. There is a 25% chance of a couple who both carry the red hair gene having a child with red hair.
The MC1R gene has strong penetrance so almost all individuals with two red hair alleles will have bright red hair. However, there are some rare cases where people carry two red hair variants but still have darker hair. This indicates other genes can influence how strongly MC1R mutations manifest.
Blonde Plus Black Hair Doesn’t Make Red
A person with naturally blonde hair will have gene variants like those in SLC24A4 that increase pheomelanin production. Meanwhile, someone with naturally black hair likely has genetic variations like those in OCA2 that maximize eumelanin synthesis.
Neither person possesses the MC1R mutations that create red hair pigment. Therefore, two blonde and black haired parents will be extremely unlikely to have a child with red hair.
The blonde parent does not contribute the pheomelanin-boosting genes needed to shift black hair to red. And the black-haired parent does not have the MC1R mutation necessary for red pigment.
There are only two far-fetched scenarios in which they could have redheaded children:
- Both parents carry recessive MC1R red hair variants inherited from distant ancestors which randomly combine in their offspring.
- There is an improbable new spontaneous MC1R mutation in the child not present in either parent.
So while possible in theory, two parents with blonde and black hair combining to make red is highly improbably in reality.
Overcoming Misconceptions
There are some common misconceptions around hair color inheritance:
- Blending hair colors: Hair colors from parents do not blend in offspring like mixing paint. Each parent passes on discrete copies of their genes.
- Simple dominant/recessive: Hair color is polygenic – determined by multiple genes, not just one. Red hair REQUIRES two recessive MC1R genes.
- Any recessive gene: Recessive genes only manifest if you inherit two copies. Getting one recessive red hair gene from one parent does NOT make red hair.
Understanding the specific genetics around MC1R, SLC24A4, OCA2, and how different combinations interact is key to explaining the inheritance of blonde, black, and red hair traits.
Conclusion
In summary, black hair and blonde hair will not combine to make red hair in offspring. Red hair is produced by two copies of a specific MC1R gene mutation, which neither black-haired nor blonde-haired individuals possess unless they are carriers. While multiple genes influence hair color, the red hair trait is controlled by the distinct MC1R gene and will not appear through blending black and blonde shades. To have red-haired children, both parents must carry and pass on the recessive red hair gene variant.