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The Gene Locus—the address of your genes

Haven’t we all read about how our ‘genes’ make up who we are— many traits like the colours of our hair and how we look depends on the genes. However, where exactly are these genes? They are in the coiled ‘chromosomes’ found in our DNA. So where exactly in the chromosomes are these genes that decide our height or our eye colour? Well, you then have to zoom the gene locus—the exact physical address of the gene on the chromosome.

Each of our cells contains 23 pairs of chromosomes, having about 20,500 genes. Although that is a significant number, our cells are super organised—these genes are not randomly scattered somewhere in the chromosome, but each of them has a specific place defined by their locus.

Scientists who study our genes refer to a ‘gene map’ that tells them the chromosomal location of each gene. Akin to how we have longitudes and latitudes to guide us on a map, distinct bands visible on a chromosome after staining with a dye describe the chromosomal locations.

So, how exactly does one decipher the gene location? A universal code is followed for naming a locus. For example, the locus 11p15, read as ‘Eleven-P-One-Five’, tells us that the gene is on chromosome 11, on its ‘p’ arm or the short arm. The numbers one and five identify the exact site in which the gene appears when a chromosome is viewed under a microscope with a suitable dye. There could also be abbreviations ‘cen’ and ‘tel’ at the end, which depict the centromeric and telomeric (end) locations. Thus, a gene locus 5qtel tells us that the gene is in the longer arm of chromosome 5, and 5pcen means that the gene is near the centromere of the short arm of the chromosome 5.

Thanks to sophisticated technologies like Next Generation Sequencing, we can now ‘sequence’ a genome and know the exact location and arrangement of these genes. This knowledge forms the base for further studies and manipulations of a particular gene of interest.