Genetics and biochemistry of hair color Human hair color

two types of pigment give hair color: eumelanin , pheomelanin. pheomelanin colors hair orange , red. humans have pheomelanin in hair. eumelanin, has 2 subtypes of black or brown, determines darkness of hair color. low concentration of brown eumelanin results in blond hair, whereas higher concentration of brown eumelanin results in brown hair. high amounts of black eumelanin result in black hair, while low concentrations result in white hair.

pheomelanin more bio-chemically stable black eumelanin, less bio-chemically stable brown eumelanin, breaks down more when oxidized. why bleach gives darker hair reddish tinge during artificial coloring process. pheomelanin continues break down, hair gradually become red, orange, yellow, , white.

the genetics of hair colors not yet firmly established. according 1 theory, @ least 2 gene pairs control human hair color.

one phenotype (brown/blonde) has dominant brown allele , recessive blond allele. person brown allele have brown hair; person no brown alleles blond. explains why 2 brown-haired parents can produce blond-haired child. however, can possible if both parent heterozygous in hair color- meaning both of them have 1 dominant brown hair allele , 1 recessive allele blond hair, dominant traits mask recessive ones parents both have brown hair. possibility of trait may appear in offspring can determined punnett square.

the other gene pair non-red/red pair, non-red allele (which suppresses production of pheomelanin) dominant , allele red hair recessive. person 2 copies of red-haired allele have red hair.

the two-gene model not account possible shades of brown, blond, or red (for example, platinum blond versus dark blond/light brown), nor explain why hair color darkens person ages. several gene pairs control light versus dark hair color in cumulative effect. person s genotype multifactorial trait can interact environment produce varying phenotypes (see quantitative trait locus).