Down's syndrome is caused by trisomy of chromosome 21, where individuals inherit an extra copy of the chromosome instead of the normal two. there is a wide range in the severity of the disease experienced by each individual, but experience lifelong intellectual disabilities and a number of associated health problems. one of the most common problems experienced by those with down's syndrome, is the early onset of alzheimer's disease (usually emerging between the ages of 30-45), with up to 75% developing dementia in their lifetime (ness et al., 2012). one of the reasons behind this is the fact that the gene encoding for amyloid precursor protein (app) is present on chromosome 21. due to this, individuals with down's syndrome produce more app. a. what is app and why would this genetic change make alzheimer's disease much more likely to develop?