Down syndrome is a genetic disorder that is typically caused by an extra copy of chromosome 21 in a person's genome. in a small number of cases, however, down syndrome occurs because a section of chromosome 21 becomes fused onto another chromosome. the type of down syndrome that occurs because a section of chromosome 21 attaches to another chromosome is an example of a genetic disorder caused by a. a frame shift mutation. b. chromosome deletion. c. a recessive allele. d. chromosome translocation.