able to identify, localize and classify a small group of genes responsible for the control of early embryonic development of the fruit fly, Drosophila melanogaster. This small group of genes was shown to be responsible in determining the body plan and the formation of body segments in the embryonic fruit fly.
Found 150 genes that were essential in the genetic control of embryonic development. Out of that 150, they found 15 genes that, if mutated, would cause defects in fruit fly segmentation. They even went further, classifying these genes into groups based on their effects on segmentation. First, gap genes control the body plan along the head-tail axis. Loss of gap gene results in a reduced number of body segments. Second, pair rule genes affect every second body segment. Loss of this gene known as "even-skipped" will result in an embryo consisting only of odd numbered segments. Lastly, segment polarity genes affect the head-to-tail polarity of individual segments.