Duplication is a type of chromosomal structural variation where a segment of the chromosome is copied and inserted into the genome, resulting in multiple copies of that segment. This can lead to genetic imbalance and have various consequences depending on the size and location of the duplicated segment. 

Types of Duplications

Duplications can be classified based on their orientation (see in above figure):

Tandem Duplications

• Definition: A duplicated segment that is inserted adjacent to the original segment.

• Example: If a segment BC is duplicated, it may appear as BC: BC on the chromosome.

• Consequences: Tandem duplications can lead to gene dosage effects where increased copies of a gene can disrupt normal cellular functions.

Reverse Duplications

• Definition: A duplicated segment that is inserted in the reverse orientation relative to the original.

• Example: If a segment BC is duplicated, it may appear as BC:CB on the chromosome.

• Consequences: The reverse orientation can disrupt the normal function of genes if the orientation affects gene transcription or regulatory sequences.