If curly hair is genetic, why do you have curly hair if none of your ancestors did?

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The answer to your question may lie in the way that hair-type genes are inherited.

First, review of some basic genetics stuff. For most genes, you have two copies of each gene that you inherited from your mother and father. For most "traditional" genes, there is a dominant and recessive version. This all has to do with gene expression and phenotype. If at least one dominant version of the gene is present, it will be expressed regardless of what the other is. The only way the recessive version will be expressed is if the dominant version is not present. This holds true for some simple traits like whether earlobes are attached or not, where the free earlobe allele is dominant (noted as "E") and the attached (noted as "e") allele is recessive.

Hair-type does not follow the nice and simple pattern of inheritance. Hair-type follows a type of inheritance pattern known as "incomplete dominance". Like the earlobe gene, there are two versions of the hair-type gene, curly (noted as C) and straight (noted as s). The incomplete dominance refers to the fact that if you have one of each version of the gene, you get a mix of the two or, in this case, wavy hair. Therefore, for hair type, CC gives curly, Cs gives wavy and ss give straight hair.
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