Finding genes on chromosomes
Your 23 pairs of chromosomes contain around 24,000 pairs of genes. If scientists have found a gene but don't know where on the chromosome it is, they use a technique called FISH - fluorescent in situ hybridisation. They prepare chromosomes on a microscope slide, tag a copy of the gene they want to find with a fluorescing dye and add it to the slide. Under a special microscope, the same gene shows up as a brightly coloured dot on the chromosome.