Genetic researchers have been working for a long time to reproduce the mysterious evolutionary step that grew legs on fish. This change eventually moved life from water to land, resulting in a explosion of walking species that took over the Earth's land and skies more than 300 million years ago.
Now, they have achieved it. They have grown legs on fish.
The key of this change is called HOXD13, part of a gene cluster that encodes the instructions that are responsible for morphogenesis in multicellular organisms. In other words: these genes control our body structure, from the number and shape of fingers on your hands to the shape of your legs. When these genes are damaged, they result in serious limb abnormalities.
On the other hand, it seems that overexpressing this gene can result in the growth of limbs. In a paper published in the scientific journal Developmental Cell, a team of genetic researchers from the Pablo de Olavide University in Seville, Spain, have discovered that HOXD13 can also be used to transform fins into limbs in zebra fishes:
Modulation of 5′Hoxd gene transcription, through tetrapod-specific digit enhancers, has been suggested as a possible evolutionary mechanism involved in these morphological transformations. Here, we overexpress hoxd13a in zebrafish to investigate the impact of increasing 5′Hoxd expression during fin development. This overexpression causes increased proliferation, distal expansion of chondrogenic tissue and finfold reduction.
In other words, by manipulating this gene they were able to grow legs on zebra fishes that resemble those in tetrapods, the superclass of animals that include all living and extinct amphibians, reptiles, birds, and mammals. In fact, the round shapes look like those of lobe-finned fish, which are the precursors of amphibians.
Their theory is that a mutation in early fish may have triggered the activation of the hoxd13 gene, resulting in the jump from sea to land, and the evolution of these animals into a walking and flying species.