Question

A number of genes controlling expression of Hox genes in Drosophila and known collectively as the Polycomb group genes (PcG) have been identified. In homozygous mutants carrying a recessive mutation in one of the PcG genes, some of the head segments and all of the thoracic and abdominal segments develop as the last abdominal segment. In other words, all of the affected segments develop as posterior segments. What does this phenotype tell you about the set of Hox genes that is controlled by this gene? Predict how – positively or negatively – the product of this PcG gene normally regulates its Hox target(s)? Briefly explain.

Answer 1

Hox genes control the body plan across head to tail direction. PcG regulate the expression of Hox gene by suppressing its expression. In mutant of PcG, the anterior and abdominal segments has been converted into posterior segments. It implies that the expression of Hox genes are repressed by the PcG in the anteior region,so that the posterior specific segments are inhibited.anterior and abdominal region are specified by the absence of Hox expression, which is achieved by PcG mediated repression.