The homeotic (Hox) genes that encode such transcription factors are critical for the proper number and placement of embryonic structures, such as legs and antennae, in the fruit fly Drosophila (see Figure 18.19). Interestingly, maize has a homolog of Hox genes called KNOTTED-1, but unlike its counterparts in the animal world, KNOTTED-1 does not affect the number or place- ment of plant organs. As you will see, an unrelated class of transcription factors called MADS-box proteins plays that role in plants. KNOTTED-1 is, however, important in the development of leaf morphology, including the production of compound leaves. If the KNOTTED-1 gene is expressed in greater quantity than normal in the genome of tomato plants, the normally compound leaves will then become “super-compound” (Figure 35.31).