Segmental Duplications (SDs) are long DNA sequences (typically defined as being > 1kb in length) that have nearly identical sequences (90-100%) and exist in multiple locations as a result of duplication events. SDs can be tandem or interspersed, and can be interchromosomal or intrachromosomal. Because SDs are so large and similar in sequence, they often result in forms of chromosomal rearrangement and can cause genome instability.  
Two Types of Segmental Duplications 
1. Interchromosomal - Sequence duplicated onto non-homologous chromosomes.
2. Intrachromosomal - Sequence duplicated onto the same chromosome, often into the same chromosome region. These duplications are typically referred to as "region- or chromosome-specific low-copy repeats (LCR)"
 Samonte, R. and Eichler, E. (2002). Segmental duplications and the evolution of the primate genome. Nat Rev Genet. 3: 65 - 72.
 Stankiewicz, P and Lupski, JR. (2002). Genome architecture, rearrangements and genome disorders. Trends genet. 18(2): 74 - 82.