Final answer:
Aneuploidy, including segmental deletions and duplications, refers to an error in chromosome number, resulting in various syndromes and genetic imbalances. Down Syndrome is an example of a syndrome caused by aneuploidy.
Step-by-step explanation:
An individual with an error in chromosome number is described as aneuploid, a term that includes segmental deletions and duplications. Aneuploidy refers to the condition where the number of chromosomes in an organism is not a multiple of the normal haploid set. It can result in various syndromes and genetic imbalances, such as Down Syndrome which is caused by trisomy of chromosome 21.