In Drosophila, loss-of-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, Ultrabithorax acts to specify the identity of the posterior thoracic segments. Similar genes were soon discovered in other animals, including mice and humans. You have found that mice possess two closely related genes, Hoxa7 and Hoxb4, which are orthologs (see Genetic Analysis 14.2 for definition) of Ultrabithorax. You wish to know whether the two mouse genes act to specify the identity of body segments in mice.

How will you create loss-of-function alleles of the mouse genes?

Key Concepts

Loss-of-Function Mutations

Loss-of-function mutations are genetic alterations that result in reduced or abolished gene function. These mutations can occur through various mechanisms, such as deletions, insertions, or point mutations that disrupt the gene's coding sequence. In the context of the Ultrabithorax gene, such mutations lead to the transformation of posterior thoracic segments into anterior-like structures, highlighting the gene's role in segment identity.

Transcription Factors

Transcription factors are proteins that bind to specific DNA sequences to regulate the transcription of genes. They play a crucial role in determining which genes are expressed in a given cell type and at what levels. The Ultrabithorax gene encodes a transcription factor that is specifically expressed in the posterior thorax, influencing the developmental fate of those segments by activating or repressing target genes.

Orthologs

Orthologs are genes in different species that evolved from a common ancestral gene and typically retain similar functions. The identification of Hoxa7 and Hoxb4 in mice as orthologs of Ultrabithorax suggests that these genes may have conserved roles in segment identity across species. Understanding orthologs is essential for studying gene function and evolutionary biology, as it allows researchers to draw parallels between model organisms and humans.