How mutations are inherited

Men and women can pass an inherited gene mutation to their sons or daughters through their sperm or eggs. When a person with a gene mutation has children, each child has a 50 percent chance of inheriting the same mutation.  

Genetics experts look carefully at a family’s medical history for signs of hereditary cancer. You can assist them by gathering medical information from relatives on both sides of your family.

Typically, a genetics expert will look at three or more generations of a family’s medical history to help predict whether family members are likely to have an inherited mutation. They will use this information to create a medical family tree known as a pedigree. 

Degrees of relatedness

When speaking about a family tree, experts use the term “degree of relatedness” to describe how closely related one family member is to another. "First-degree relatives” share half of their DNA. If a person has an inherited mutation, each of their first degree relatives have a 50 percent chance of testing positive for the same mutation. Second-degree relatives share one fourth of their DNA, third-degree relatives share one eigth of their DNA, and so on. 

• First-degree relatives
  • Siblings
  • Children
  • Parents
• Second-degree relativesHalf-siblings
  • Uncles and aunts
  • Grandparents
  • Grandchildren
  • Nieces and nephews
• Third-degree relatives
  • Cousins
  • Great grandparents
  • Great-aunts and Great-uncles