When a person with red hair and a person with black hair have a baby together, the resulting hair color of the child depends on the genotypes of the parents. Human hair color is controlled by the amount of eumelanin (black/brown pigment) and pheomelanin (red/yellow pigment) produced by melanocytes in the hair follicles. Several genes influence the ratio of eumelanin to pheomelanin that determines hair color. The MC1R gene plays a major role in regulating this ratio. Specific variants of this gene are associated with red hair. The combination of genotypes from both parents determines which variants the child inherits and the resulting hair color.
Genetics of Hair Color
Human hair color is primarily determined by two types of melanin pigments:
- Eumelanin – brown/black pigment
- Pheomelanin – red/yellow pigment
The relative amounts of eumelanin and pheomelanin produced in the hair follicles determine someone’s hair color. Several genes are involved in regulating melanin production and deposition, including:
Of these, MC1R plays the biggest role in determining the ratio of eumelanin to pheomelanin. Specific variants in this gene are strongly associated with the red hair phenotype.
MC1R Variants Associated with Red Hair
The MC1R gene provides instructions for making the melanocortin 1 receptor protein, which is involved in controlling melanin production. Several variants in this gene are associated with red hair:
|D84E||Impaired receptor function, more pheomelanin|
|R142H||Impaired receptor function, more pheomelanin|
|R151C||Impaired receptor function, more pheomelanin|
|R160W||Impaired receptor function, more pheomelanin|
|D294H||Impaired receptor function, more pheomelanin|
These variants lead to impaired MC1R function and favor pheomelanin production, resulting in red hair. An individual only needs to inherit one of these variants from a parent to have red hair.
How Genotypes of Parents Determine Hair Color Outcomes
When a person with red hair and a person with black hair have children, the resulting hair color depends on the specific MC1R genotypes inherited from each parent. There are several possibilities:
Both Parents Have MC1R Variants for Red Hair
If both the red-haired and black-haired parents carry two copies of MC1R red hair variants, they will pass one of these variants on to the child. The child will have red hair.
One Parent Has Two Copies of MC1R Variants, One Parent Has None
If the red-haired parent has two copies of red hair MC1R variants, while the black-haired parent has no copies, the child will inherit one red hair variant from the former parent. The child will have red hair.
Both Parents Carry One Copy of an MC1R Variant
If both parents carry just one copy of an MC1R red hair variant, along with one normal copy, there is a 50% chance of the child inheriting a red hair variant from either parent. The child would then have red hair. There is also a 50% chance the child inherits two normal copies and has black hair.
One Parent Has One Copy of an MC1R Variant, One Has None
If only one parent carries a single copy of a red hair MC1R variant, while the other has no variants, there is a 50% chance the child will inherit the red hair variant and have red hair. There is a 50% chance they inherit the normal copy and have black hair.
Other Genetic and Environmental Factors
While MC1R variants account for most cases of red hair, other genetic and environmental factors can also influence hair color, including:
– Other hair color genes like OCA2, SLC24A5, TPCN2, and KITLG
– Quantity and distribution of melanocytes in hair follicles
– Age/growth stage of hair
– Sun/UV light exposure
– Oxidative hair treatments/dyes
These factors may explain occasional discrepancies between MC1R genotypes and observed hair phenotypes. The exact shade of red hair can also vary depending on the specific variants inherited.
In summary, when a person with red hair and a person with black hair have a child, the resulting hair color depends primarily on the MC1R genotypes inherited from each parent. Specific variants in this gene impair melanocortin 1 receptor function, favoring pheomelanin production and resulting in red hair. Inheriting one of these red hair variants from either parent is typically enough for a child to have red hair themselves. The possibilities are:
– Child inherits red hair variant from each parent – red hair
– One parent has two copies of red hair variant, one has none – red hair
– Both parents have one copy of red hair variant – 50% chance red hair
– One parent has one copy of red hair variant – 50% chance red hair
While MC1R genotypes are the main determiner, other genetic and environmental factors can also influence the final hair color. The interplay between all these factors explains the range of red hair shades seen.