For over thirty years research geneticists have been studying the chromosomes of the species Drosophila (fruitfly). These chromosomes, suitably prepared and stained, have an appearance similar to earthworms with light and dark bands around them. They are large enough to be seen clearly under a high power light microscope. These patterns of bands reflect the genetic heritage of the fly and can be used to trace inherited traits. Researchers examine enlarged photomicrographs of the chromosomes to locate sections with closely similar band patterns. An application of pattern recognition techniques to this problem has yielded a semi-automatic method of detecting band patter similarities. The chromosome photographs are optically scanned in a specially constructed densitometer. This generates a plot of optical density versus position along the length of the chromosome. The density plot is measured to determine the widths and spacings of the bands.