six drosophila melanogaster tumor suppressor genes causing malignant or benign tumors in specific cell types are described . 
 the wild - type alleles of these genes are instrumental in the differentiation of particular cell types . in the homozygous state , 
 recessive mutations in the genes interrupt the differentiation of the cells and thus cause their uncontrolled , autonomous , lethal proliferation . 
 the tumors show all major characteristics of malignant and benign neoplastic growth . 
 genomic sequences of four of the genes have been identified and are currently being characterized . 
 imagesfigure 1.figure 2.figure 2 .