Why can a germline mutation be passed to a child?

A germline mutation can be passed to a child because it occurs in the reproductive cells—specifically the sperm or ova—that unite during fertilization to form the offspring.12

Unlike somatic mutations, which affect only the body cells of an individual and cannot be inherited, germinal mutations alter the genetic constitution of the gametes. Because each parent contributes one set of chromosomes to their child, any mutation present in the DNA of the reproductive cells is transmitted to the next generation. Once inherited, this mutation becomes part of the child's genotype, meaning it will be present in all of the child's cells.123

This process is a fundamental aspect of heredity, serving as a primary source of genetic variation that can lead to evolutionary change or, in some cases, result in inherited diseases.132