Many animals have repurposed genes that were originally involved in the development of other structures, such as fins or wings, to develop limbs. For example, the Hox genes, which are essential for specifying the identity of different segments of the body along the anterior-posterior axis, are also involved in limb development. In vertebrates, the Hox genes are expressed in different combinations in the developing limb to specify the different segments of the limb, such as the upper arm, forearm, wrist, and hand.

Eyes:

The eyes of different animals have evolved independently multiple times, and as a result, they have often repurposed genes that were originally involved in other functions. For example, the Pax6 gene, which is essential for the development of the eye in vertebrates, is also expressed in the developing brain, where it is involved in the development of the optic tectum, a structure that is involved in visual processing. In addition, the Pax6 gene is also expressed in the developing pancreas, where it is involved in the differentiation of pancreatic islet cells.

The repurposing of genes for different functions is a common theme in evolution. It allows animals to evolve new structures and adaptations without having to start from scratch. By reusing genes that are already present in the genome, animals can quickly and efficiently adapt to new environments.