The Hoxd9–13 genes are thought to specify digit identity (see Figure 18.18). You wish to examine the effect of loss-of-function alleles in developing limbs. How would you construct a mouse in which the function of Hoxd9–13 is retained during anterior–posterior embryonic patterning but is absent from developing limbs?

Key Concepts

Hox Genes

Hox genes are a group of related genes that determine the body plan and the identity of body segments in animals. They play a crucial role in embryonic development by regulating the expression of other genes, influencing the formation of structures such as limbs and digits. In particular, the Hoxd9–13 genes are involved in specifying digit identity along the anterior-posterior axis of the limb.

Loss-of-Function Alleles

Loss-of-function alleles are mutations that result in the reduced or abolished function of a gene. In the context of genetic studies, these alleles are used to investigate the role of specific genes by observing the phenotypic consequences when the gene's function is impaired. In this case, examining the effects of loss-of-function alleles in Hoxd9–13 will help elucidate their role in limb development.

Conditional Knockout

A conditional knockout is a genetic engineering technique that allows researchers to inactivate a gene in specific tissues or at specific developmental stages. This is typically achieved using Cre-loxP technology, where the Cre recombinase enzyme excises the gene of interest only in designated cells. In this scenario, a conditional knockout of Hoxd9–13 in limb tissues would enable the study of their function while preserving their activity in other regions during embryonic development.