The exact location of a gene on a chromosome is called?

• A. Region
• B. Locus
• C. Position
• D. Site

Answer: (B)

In genetics, the exact fixed position of a gene on a chromosome is called its locus. The locus designates the precise spot where the gene sits, and it’s the term used when mapping genes or describing where mutations occur. Other words like region or site can be broader or context-specific, and position is too general to pin down a definite place. A locus stays the same location on the chromosome, even though the gene may have different versions (alleles) on the two homologous chromosomes. In practice, scientists describe loci using chromosome number and coordinates (for example, a specific band on a chromosome) to pinpoint where a gene is located.