Chapter 17, Problem 26P

In Drosophila, loss $\text{-}$ of $\text{-}$ function Ultrabithorax mutations result in the posterior thoracic segments differentiating into body parts with an identity normally found in the anterior thoracic segments. When the Ultrabithorax gene was cloned, it was shown to encode a transcription factor and to be expressed only in the posterior region of the thorax. Thus, Ultrabithoraxacts to specify the identity of the posterior thoracic segments. Similar genes were soon discovered in other animals, including mice and men. You have found that mice possess two closely related genes, Hoxa $7$ and Hoxb $7$, which are orthologous (see Genetic Analysis $14.2$ for definition) of Ultrabithorax.

How will you determine where and when the mouse genes are expressed?

How will you create loss $\text{-}$ of $\text{-}$ function alleles of the mouse genes?

How will you determine whether the mouse genes have redundant functions?