Is it possible for a black haired parent and a brown haired parent to have a child with blonde hair if all the grandparents of said child has either black brown or dark auburn hair?

Answer 1

You should be aware that the color of a child's hair can change as it grows up. When I was 7 my hair was silvery blond - by the age of 20 I was dark brown.

On top of this the genetics for hair color are not simple (there is more than one gene involved). Look in the link I will place below. Yes, this is perfectly possible. Genes (sections of your DNA in each cell) determine, among other things, hair colour and are either 'recessive' or 'dominant''. the two different kinds of gene (dominant or recessive) are called alleles. The allele for brown or black hair is dominant over the blonde hair allele which means that when a child inherits a gene for hair colour from his parents then if one of the pair is a dominant gene - i.e. the 'brown hair gene' then that child will have brown hair whether or not they have a blonde hair gene as well. This means that it is more likely that a child has brown or black hair rather than blonde. Let's look at an example: 2 parents have 2 different allele Blonde/Brown (mother) and Blonde/Brown (father). They will therefore both have black or brown hair as they contain brown allele which mask the blonde allele in their chromosomes because the brown allele is dominant. Let's call the genes they have Bl(m) Br(m) Bl(f) Br(f) where Br=Brown, Bl = Blonde, m = mother and f = father. When they have a child then he will inherit one allele from his mother and one from his father. The possibilities of what he inherits are either 1. Bl(m) Bl(f) or 2. Bl(m) Br(f) or 3. Br(m) Bl(f) or 4. Br(m) Br(f) The only combination that produces a blonde child is the first one where both alleles are blonde. In the other three there exists a brown allele and, because brown alleles are dominant, the child will have brown hair irrespective of the fact that in two of the possibilities there is a blonde allele as well. Therefore there is only a one-in-four chance of parents with mixed genes having a blonde child, but it is still perfectly possible. Going back a generation to grandparents means that if all their grandparents had brown or black hair, then, again, the blonde allele could be lying dormant until the time when it is able to show up when it is matched with another blonde allele so that a brown allele cannot mask its effect. In my own family, my cousin's daughter has bright red hair (another recessive allele) although her parents and grandparents are brown haired. My father was red haired but I have brown. So to find the origin of the red-hair-allele we would have to look further back in out family history to find an ancestor of both my father and my cousin's parents. Asit happens our great great grandfather had red hair - and so he passed this on to the family, only to show up rarely in further generations where it was not masked by a more dominant allele like brown or black hair. Sad to say, many marriages have hit the rocks because of a child being suspiciously born with the same colour hair as the milkman or the husband's best friend... but if the couples had taken a lesson in elementary genetics, I am sure that the divorce courst would have been far less busy.