13. By which mechanisms discussed in this chapter do the following situations alter Hardy-Weinberg equilibrium? a. In ovalocytosis (MIM 166910), a protein that anchors the red blood cell plasma membrane to the cytoplasm is abnormal, making the membrane so rigid that parasites that cause malaria cannot enter. b. In the mid-1700s, a multitoed male cat from England crossed the sea and settled in Boston, where he left behind many kittens, about half of whom also had extra digits. People loved the odd felines and bred them. Today, in Boston and nearby regions, multitoed cats are much more common than in other parts of the United States. c. Many slaves in the United States arrived in groups from Nigeria, which is an area in Africa with many ethnic subgroups. They landed at a few sites and settled on widely dispersed plantations. Once emancipated, former slaves in the South were free to travel and disperse. d. About 300,000 people in the United States have Alzheimer disease caused by a mutation in the presenilin-2 gene. They all belong to five families that came from two small villages in Germany that migrated to Russia in the 1760s and then to the U.S. from 1870 through 1920.