Genes that cause Prader-Willi syndrome and Angelman syndrome are closely linked along chromosome 15. Although people with these syndromes usually do not reproduce, suppose that a couple produces two children with Angelman syndrome. The oldest child, Pat, grows up and has two children with Prader-Willi syndrome. The second, Robin, grows up and has one child with Angelman syndrome.

a. Are Pat and Robin's parents both normal or does one of them have Angelman or Prader-Willi syndrome? If one of them has a disorder, explain why it is the mother or the father.

b. What are the sexes of Pat and Robin? Explain how you determined this.