Madhu Gopel, of Ilam Primary School, asks :-

Why do we have different hair colours?

Clive Ronson, a geneticist at Otago University's School of Medicine, responded.

Differences in hair and skin colour between people are due to differences in the amount and type of a chemical called melanin (the same chemical that allows some of us to go brown after exposure to the sun), and the way it is packaged into hair and skin cells. Melanin is a complex mixture of related chemicals and is produced in special cells called melanocytes. The melanocytes secrete melanin into keratinocytes, the cells that form hair fibres, and also into skin cells. Melanin is of two main types: eumelanin which is brown or black, and pheomelanin, which is yellow or red. The relative absence of both melanin types is associated with white hair; more eumelanin than pheomelanin with brown or black hair; and more pheomelanin with red hair.

The MC1R (melanocortin 1 receptor) gene encodes a protein that, when activated by hormones, causes an increase in the ratio of eumelanin to pheomelanin, leading to brown or black melanin at the expense of yellow or red melanin.

Differences in hair (and skin) colour between people are one of the most striking human characteristics. These differences are largely inherited and hence under genetic control. Surprisingly we dont know much about the genetics of hair colour in humans and it needs more study. We do know that red hair is a recessive trait, meaning that particular variants of MC1R need to be inherited from both parents to give a high chance of having red hair.

Similar diversity in the MC1R gene is known to underpin hair and skin colour changes in a wide range of animals, including dogs - for example, Red Setters are red and Golden Labradors golden due to the same MC1R variant causing an excess of pheomelanin, with other genes determining the red versus the gold.