What were the chances of my parents have a blonde child?

My mom has dark brown hair and my dad has black hair. All of my grandparents had dark hair except for my grandmother who had blonde hair. I'm just wondering because all my brother and two sisters have dark and my cousins do too so I'm like the only blonde.What were the chances of my parents have a blonde child?
From a dark haired couple (your parents) with the recessive blond allele (your parents), there is a 1/4 chance that they will have a blonde child. From your grandparents, it's a little more complicated:


For two dark-haired people to have a dark haired child with a recessive blonde allele, the probability is 1/2. And on your other parent's side, the probability that a dark haired man and a blonde-haired woman have a child with dark hair and a recessive blonde allele, the probability is 1. So for the grandparents you had, the probability that your parents would turn out the way they did is 1/2. And then for your parents to have a blonde child (you), the probability is 1/4.





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Therefore, the probability that you would be blonde is 1/8, given three dark-haired grandparents and one blonde-haired grandparent.