Prologue, 3   PART I FOUNDERS The Life and Death of Hannah, 11 Gregor Mendel, 17 Alois Alzheimer, 21   PART II INTO THE WILDERNESS The Descendants of Hannah and Shlomo, 33 Mendel's Heirs, 41 Alzheimer's Disease at Midcentury, 55 Enter Genetics, 59 New Seeds Are Sown, 69 No Longer Alone, 75 Twin Pillars of Hope, 79 A Transmissible Virus?, 87 Base Camp, Circa 1980, 95   PART III THE ASCENT The New Basis for Linkage Maps of the Human Genome, 105 The Quest for the Huntington's Disease Gene, 119 Charles, 131 Peter St. George-Hyslop and the Link to Chromosome 21, 135 A Gene for Amyloid, 149 A Siege of the Soul, 155 Elizabeth W. and the Second Family from Bobruisk, 159 A Unity of Heart and Mind, 163 Russia Once Again, 171 The Twenty-one Pedigrees of Nina Ivanovna Voskresenskaya, 175 How Many Genes?, 181 The Third Dove Goes Forth, 187   PART IV THE PATH AHEAD Lost Tribes, 193 The First Abnormal Gene Is Found, 205 New Sightings, 219 Mutual Aid as a Factor in Evolution and in Genetic Research, 227 Hannah's Heirs, 237   EPILOGUE Landfall, 241 Hannah's Gene, 259 Notes, 269 References, 287 Index, 303 [-310]