How are chromosomes ‘painted’? Your 23 pairs of chromosomes
contain around 24,000 pairs of genes. FISH – fluorescent in situ
hybridisation – can be used to ‘paint’ chromosomes. Scientists
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.