Which chromosomal mutation increases the number of copies of a chromosome segment?

• A. Translocation chromosomal mutation
• B. Duplication chromosomal mutation
• C. Inversion chromosomal mutation
• D. Deletion chromosomal mutation

Answer: (B)

Increasing the number of copies of a chromosome segment is caused by a duplication. In duplication, a segment of the chromosome is copied, and that extra copy remains in the genome, raising the gene dosage within that region. This can happen during flawed DNA replication or during meiosis when unequal crossing over occurs, leading to tandem or dispersed extra copies.

In contrast, a translocation relocates a segment to another chromosome or a different place on the same chromosome without necessarily changing how many copies exist. An inversion flips the segment’s orientation but doesn’t change copy number, and a deletion removes material, reducing the number of copies.