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Before scientists test new drugs, diagnostic procedures, and therapeutics on humans, they usually start by evaluating how those things perform in animals.

But sometimes, their choice of animals seems... maybe not that representative of human biology. Like one common test subject is a fruit fly. Except, fruit flies have been behind some of the most ground-breaking discoveries in physiology and medicine. And they're helping us understand everything from inheritance all the way to cancer and sleep.

In some ways, the reason we use fruit flies in the lab are pretty basic, like they're cheap to keep and maintain for example.

But there are also bigger reasons, For one, the flies are much easier to study than complex vertebrates, especially when it comes to genetics.

Their whole collection of genetic material consists of just four pairs of chromosomes compared to our 23. That means it's easier to study what genes do and how they interact.

Their simpler genes and structure also make fruit flies relatively easy to genetically modify, which allows us to test what happens when you break things. And, of course, their short life cycle is useful in a research setting too. But like, here's the key thing, fruit flies also have a shocking amount in common with us.

They have equivalent genes for 60% of the human genome. They also have a similar gene for 65 to 75% of the human genes that have been linked to diseases like Alzheimer's, Diabetes, and many cancers. And thanks to those similarities, they've shown us quite a bit.

Fruit fly research officially began in the early 1900s when the now famous biologist Thomas Hunt Morgan was studying how genes are inherited. By this point in history, we knew inheritance was a thing, but we didn't quite understand how it worked, so Morgan was looking into it.

In his research, he found a male fruit fly with white eyes instead of the typical red [eyes], and he observed how this trait was passed on by breeding different fruit flies together.

Ultimately, he discovered that only male flies ever had these white eyes, and that the genetic factor that determined eye color was on the same chromosome that determined sex.

In doing so, he was the first to link the inheritance of a trait to a specific chromosome.

And it not only earned him a Nobel prize, but it opened the door to most of what we understand about inheritance in humans today, because we also have traits controlled by our genes on our sex chromosomes.

One example is red-green colorblindness, which is passed down on the X-Chromosome. That's why people who are X-Y and only have one copy of this chromosome are more likely to be colorblind, usually men. People with two X-Chromosomes would need to have the gene for colorblindness on both of them, which is less likely.

Meanwhile, one of Morgan's students named Hermann Muller made another revolutionary discovery using fruit flies that earned him a Nobel prize.

He found that x-rays and other ionizing radiation can cause genetic mutations by breaking apart chromosomes.

This can cause DNA to get deleted, duplicated, swapped around, or just inserted into the wrong place, all of which can be passed on to offspring.

Thanks to his work, we now take precautions when taking x-rays, like using those heavy lead aprons you might wear at the dentist.

But this work had implications beyond inheritance, too.

Since they had to keep track of all these rearrangements, scientists ended up creating records of what sorts of genetic information lived in different parts of the chromosome.

And that led us to broader discoveries, like it taught us more about how embryos are developed.

Specifically, it let us find one of the signaling pathways that controls development within an embryo. 

A signaling pathway is how cells communicate with each other.

This one is called Notch, because researchers found it while trying to figure out what made certain fruit flies develop notches in their wings.

But, lots of other animals have it, including mammals like us.

Through a lot more research spanning decades, scientists not only learned how it communicates with other cells, but that this pathway is critical for the development of things like neurons, blood cells, the heart, bones, and skin.

Through this pathway, cells are told what to become during differentiation: the process where they transition from one type of cell to another.

Notch also controls cell multiplication, survival, and equilibrium.

That means that any mutations or abnormal signaling can result in developmental disorders and cancers.

And really, that's only the start of the list.

The potential applications of fruit flies in biomedical research are far from exhausted.

They're being used to study wound healing, new bio-engineering technologies, the effects of new pharmaceuticals, how the brain works, and cancer as a whole.

Like in the 2010s, the number of cancer studies using fruit flies increased exponentially.

And they're teaching us about everything from how tumors spread all the way to why cancer cells can resist medication.

Fruit flies have even taught us about sleep.

It turns out that fruit flies need to rest just like we need to sleep, making them a good model for studying the mechanisms and function of sleep, because we still don't know why sleep is a thing we need.

By looking at their genetics, researchers have identified genes and signaling pathways that affect fruit fly sleep cycles, as well as the regions of the brain responsible.

So, while these results don't have direct applications to humans yet, they could lead to a better understanding of the differences in sleep habits.

Really, fruit flies may look nothing like us on the outside, but, because of their biology and their genes, there's a practically endless number of things that they could teach us.

So, the next time you see a bunch of them hovering around your fruit bowl, you may want to thank them before getting out the fly swatter.
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