Why do we have fingers on our hands, and not on our heads? Hox genes. These are responsible for putting body parts in the right locations. They are like the body's genetic blueprint, and they're not just for humans. These genes are the foundation of the head-to-tail organization in other animals, too, such as flies, worms and mice. Occasionally, something goes awry, which can cause an insect to grow legs out of its head instead of antennae or genetic disorders in humans, such as malformed hands or feet.

What Are Hox Genes?

First, let's understand the bigger picture. Hox genes are a subset of Homeobox genes, which are a subset of Homeotic genes, the master regulators that control the development of whole-body segments or structures, according to Khan Academy.

When they are overactivated or inactivated by a mutation, body structures such as limbs can still develop, but they may end up in the wrong place. For example, normal insect anatomy means that a bug should have six legs growing out of its thorax, antennae growing out of its head and wings on its back. But a genetic mutation could mess up the normal body plan (the basic structure of the animal) and cause a peculiar-looking insect that may not be able to fly.

How They Were Discovered

According to Stanford University's The Dish on Science, Thomas Hunt Morgan discovered the Hox gene family in 1915. Scientists in his research lab noticed that some fruit flies had an extra set of wings. They investigated and found the gene that caused the mutation and named it the Hox gene. During this era, William Bateson, the British biologist who founded and named the science of genetics, also made similar observations in other organisms. He studied:

  • Crayfish with extra oviducts (reproductive tubes)

  • Bees with legs where antennae should have been

  • Humans with extra fingers, toes or ribs

Broader Implications

In the century since Hox genes were discovered, scientists have continued to investigate how these genes create blueprints for our bodies and why they sometimes go wrong. In 2019, Technology Networks reported that an international group of researchers found a method that can systematically identify the role each Hox gene plays in a developing fruit fly.

"The genome, which contains thousands of genes and millions of letters of DNA, is the most complicated code ever written," said Richard Mann, PhD, one of the researchers. "Deciphering this code has proven so difficult because evolution wrote it in fits and starts over hundreds of millions of years. [This] study offers a key to cracking that code, bringing us closer than ever to understanding how Hox genes build a healthy body, or how this process gets disrupted in disease."

Not only do these genes play an important role in embryo development, but they also seem to have a role in certain types of cancers, such as leukemia, according to News Medical.

Further research on these mysterious genes could help us understand both human and animal genetics — and maybe even provide the foundational science needed to cure certain genetic disorders and other diseases.