Chromosomal Mutations or Aberrations: Duplication

The presence of a part of a chromosome double of the normal complement is known as 'duplication'.

• A chromosome segment breaks and reattaches abnormally.
• The broken piece may attach to a homologous or non‑homologous chromosome or behave as an independent fragment if it has a centromere.
• Result: some genes occur in more than two doses (increased gene dosage).

1. Extrachromosomal: Duplicated part behaves as a separate chromosome when it has a centromere.
2. Tandem: Duplicated segment lies just beside the normal segment, in the same order.
3. Reverse tandem: Duplicated segment lies beside the normal segment but in reverse gene order.
4. Displaced: Duplicated segment is present away from the original section.
5. Transposed: Duplicated segment is attached to a non‑homologous chromosome.

Chromosome Pairing Effect:

During pairing of homologous chromosomes, duplication causes unequal or looped‑out configurations, similar to those seen in deletions.

Biological Effects:

• Effects on viability are generally less harmful than those of deficiencies (deletions).
• Carriers of duplications show abnormalities in bodily characters, which help in identifying the duplication.

Evolutionary Importance:

• Duplication increases the number of genes in a cell.
• Extra copies of the same gene can change in different directions over time, allowing new functions to evolve without disturbing the normal function.