In Drosophila, both fushi tarazu (ftz) and engrailed (eng) genes encode homeobox transcr...

In Drosophila, both fushi tarazu (ftz) and engrailed (eng) genes encode homeobox transcription factors and are capable of eliciting the expression of other genes. Both genes work at about the same time during development and in the same region to specify cell fate in body segments. To discover if ftz regulates the expression of engrailed genes, if engrailed regulates ftz, or if both are regulated by another gene, you perform a mutant analysis. In embryos (ftz/ftz) engrailed protein is absent; in engrailed embryos (eng/eng) ftz expression is normal. What does this tell you about the regulation of these two genes—does the engrailed gene regulate ftz, or does the ftz gene regulate engrailed?

¦ HINT: This problem involves an understanding of regulation of gene expression by trans-acting factors (see Chapter 17). The key to its solution is analysis of the genetic background of each mutant strain.