They are no more alike than any sibling set, sharing about 50 % of their genetic markers in a unique combination of genes from both parents. (verywellfamily.com)
In such cases, she would have received the defective gene from both parents; specifically, an affected father and a mother who is either a carrier or is affected herself. (ckcsc.org)
This means affected individuals receive a flawed gene from each parent in order to have symptoms. (sciencedaily.com)