Inheritance Patterns, Pedigrees, and Genetic Disorders Practice Test

Rett syndrome is a sex-linked dominant disease found on the X-chromosome. If the offspring of a certain cross have a 50% chance of receiving the disease, regardless of gender, which of the following statements is true?

Researchers are studying a disease that causes neurological deficits in humans. They have identified the disorder as autosomal dominant, but notice that about 20% of people with the dominant disease allele do not express any of the associated neurological impairment. What genetics term explains this phenomenon?