Which chromosomal aberration can create a fusion gene by joining segments from two different chromosomes?

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

Answer: (A)

Fusion genes form when pieces from two different chromosomes become joined, producing a new transcript that can encode a novel protein. This most often happens through a translocation, where a segment from one chromosome moves onto another chromosome and fuses with a gene there. A classic example is the BCR-ABL fusion resulting from a t(9;22) translocation, which combines parts of the BCR and ABL genes and can drive leukemia.

Deletions remove material on a chromosome, usually eliminating genes rather than creating a new cross-chromosome gene. Duplications increase copy number of a region on the same chromosome, altering dosage but not creating a fusion between chromosomes. Inversions flip a segment within the same chromosome, changing gene order rather than linking segments from different chromosomes.