Genetic Advice
A friend comes to you asking, “Is it possible that two parents with dark brown hair could have a child with blonde hair when only one grandparent on each side has blonde hair?” I would answer immediately, “Yes, they can.” My husband and I both have brown hair and our oldest boy has blonde hair. Genetics is a wonderful thing that makes each individual unique. Many people don’t understand how a child can look different than their parents. The answer is in dominant and recessive genes inherited from their parents.
Every person gets two sets of genes. One set comes from the mom and one from the dad. A dominant gene is a strong gene that will show up whether one or two copies of that gene is inherited. A recessive gene is not as strong of a gene and only shows up when two of those genes are inherited. In other words, a child
must inherit a recessive gene from both mom and dad in order for it to manifest.
In the example above, it is important to know that brown hair is a dominant gene and blonde hair is a recessive gene. It is important to know that because one of the child’s maternal grandparents and one of the child’s paternal grandparents has blonde hair. This means that one grandparent on both the mother’s and the father’s side has two recessive genes for blonde hair. Since the child’s parents both have brown hair and we know brown hair is a dominant gene than we also know that one member of each set of grandparents has a dominant brown hair gene.
Below are charts that could be used to show how it is possible to have a child with blonde hair as in the example above.