Which of the following refers to a specific sequence of genes on a chromosome?

A gene locus refers to the specific physical location of a gene on a chromosome. Each gene occupies a distinct place, known as its locus, which is essential for identifying where genes are located within the genomic structure. The concept of gene locus is fundamental in genetics, as it helps researchers and geneticists understand gene mapping, inheritance patterns, and the relationship between genes and their respective traits.

The other terms relate to genetics but do not specifically denote a location on a chromosome. An allelic pair describes two alleles of a gene, often responsible for different traits but does not refer to a physical position. Chromatids are the duplicated forms of a chromosome that are joined at a region called the centromere during cell division and refer to the structure of chromosomes rather than their specific genetic locations. A genomic region generally indicates a broader area of the genome and is not specific to individual gene locations. Thus, the specificity of a gene locus makes it the correct choice in this context.