Genes contain the hereditary information that is passed down from parent to child.
They serve as the blueprint for many features. Everyone has two copies of a gene called BRCA1 in the cells of their body, one inherited from their mother and one from their father. In most people, both BRCA1 genes function normally. But in some individuals, one copy carries a misspelling. This change, or alteration, can occur at hundreds of different sites along the BRCA1 gene.