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Go to Brilliant.org/SciShow to learn  how you can take your STEM skills to the next level and get 20% off  an annual premium subscription! [♪ INTRO]. In the last few years, we’ve seen  scientists make big advancements with organoids — these are  clumps of tissues made in the lab that mimic the biology of a full-blown organ.

While it’s still a relatively  new technique, scientists have been able to make organoids  of everything from intestines to lungs and even brain tissue. These mini-organs in a dish are  models that help us understand the functions of those organs without  having to have the full version at hand. Recently, Dutch researchers publishing  in the journal Cell Stem Cell figured out a way to make organoids  that resemble tear glands.

And weirdly enough, they can actually cry. The scientists started by collecting  stem cells from the tear glands of mice and from human participants,  and then they grew them with some chemicals known to  be involved in eye development. Once they had organoids to work with, the next challenge was getting them to cry.

Unfortunately, cells in a dish don’t  quite have the emotional response to like, Titanic, that we do,  so you can’t just show them a movie and hope for the best. And so, instead of making an  organoid read The Fault In Our Stars, the researchers exposed the tissue  to one of the neurotransmitters that causes humans to get all  misty eyed — noradrenaline. Sure enough, when the organoids were  exposed to the neurotransmitter, they swelled up with fluid.

But the researchers weren’t done there. They took some of the stem cells  made from mice, and then deleted a gene called Pax6, which is  involved in eye development. Then they raised those cells  into tear gland organoids lacking that important gene.

These organoids not only grew  more slowly, but weren’t able to produce tears, which  means this gene was crucial for proper tear gland development. Understanding how these organoids  produce tears should help human   patients with conditions like Sjögren’s syndrome, an autoimmune disease that leaves  the sufferer with dry eyes and mouth. Sjögren's patients tend to have  less of the protein made by the Pax6 gene, so this research  model should help us study how that affects tear production.

These model tear glands aren’t  all the way there yet, though. They’re made of one type of cell: ductal cells. But experiments in mice told  the team that they were missing at least one key cell type.

So their future work will focus  on making more complete models. That means we're still a long time away from fully lab-grown tear gland transplants. But the research group is  hopeful that their work will lead to a better lab model, so that other researchers can study tear-related diseases more accurately.

In more eye-related news, an  article published last week in. Science Advances suggests that the genetics of eye color are way more complex than we imagined. In the paper, an international  team of scientists analyzed the genomes of almost two hundred  thousand people and identified fifty new genes that are involved in eye color.

And that’s a big departure from  how you may have learned about the genetics of eye color in school. See, in the past we thought of  eye color as a Mendelian trait. That means a trait governed  by just one or a few genes, so it’s easy to predict how  that trait will be passed on.

If you knew the eye colors of both  parents, then you could predict the eye color of the offspring,  since the gene for brown eyes was thought to be dominant  over the gene for blue eyes. But eye color doesn’t just break  down into brown, green, or blue. There’s a lot more variation  than one gene can account for -- like shades of brown.

In fact, previous research had found  around a dozen genes linked to eye color. Eye color is still inherited from your  parents, but more than one gene is involved. So in this recent study, the  researchers did something called a genome-wide association study  — which is a way to capture the influence of a large number of  genes across a large population.

Then they asked participants to  self-categorize their eye color, and if they had brown eyes, to  include exactly which shade of brown. Now, the vast majority of  participants had European ancestry, so they also recruited  about sixteen hundred people with Asian ancestry, and did  the same genetic analysis. All in all, the analysis found fifty  genes that influenced which eye

color the participant had -- in  addition to the ones already known.

Only eight of these fifty genes  had already been associated with some kind of pigmented  trait, like hair or skin color. So even though variations in these  traits are frequently seen together, like blonde hair with blue eyes, those  traits are influenced by different genes. The researchers also found that  the same genes influence eye color in people of both European and Asian ancestry.

Meaning the same genes that  influence blue or brown eye color also help determine individual shades of brown. So it’s not a simple matter of  brown being dominant over blue. Now, there are a few different  diseases that involve eye pigmentation — conditions like albinism or pigmentary glaucoma.

The research group hopes their  findings will help shine some light on how those work and how to treat them. But it also shows us that the  simplest things aren’t always as simple as we thought -- and  there’s always more to understand about the world and ourselves. The folks at Brilliant want to help you with that.

Because the best way to learn  is by just jumping in and doing. Which is why they’ve got tons  of courses in math, science, engineering, and computer science,  with hands-on interactive examples that will help you learn by  doing, not by memorizing. There’s a course on computational  biology, which among other things, will help you learn more about the  math behind the genome-wide studies we talked about today.

And, of course, there is much more than that. You can check them out at  Brilliant.org/SciShow, and if you want to sign up, you can save 20% off  an annual premium subscription. So thanks! [♪ OUTRO].