In this episode of Tiny Show and Tell Us, we cover the science of rainbows and why double rainbows are always mirror images. Then we talk about mysterious, yet super common, chromosomes called Robertsonian chromosomes that seem to have a significant impact on human health.
Transcript of this Episode
Sam Jones: Welcome to Tiny Show and Tell Us, the bonus series where you write in with your favorite science news or factoid. We read your email aloud and then dive deeper. I'm Sam Jones and I'm here with my co-host Deboki Chakravarti.
Deboki Chakravarti: Hi, Sam. I'm excited for this because it is always fun to get to read what people send us and to talk about it and to see where it takes us. Before we get started, we should just give a big thank you to science journalist Ariana Remmel who did the research for this episode, and also we should remind all of you listeners that we want you to write to us. That's what makes these episodes possible.
So email tinymatters@acs.org or fill out the form linked to the episode description with your Tiny Show and Tell Us. Okay. Sam, do you want to kick things off?
Sam Jones: Totally. So I'm going to share a Tiny Show and Tell Us from listener Tammy. Tammy wrote in saying in a rainbow, the more prominent the color red is, the larger the raindrops are. Also in a double rainbow the colors are reversed.
Deboki Chakravarti: Oh.
Sam Jones: I haven't really thought about rainbows other than that looks cool.
Deboki Chakravarti: Yeah.
Sam Jones: So I'm excited to talk about this, to talk about some rainbow physics, which you know鈥� I love my physics. So let's do this.
Deboki Chakravarti: This is going to be fun for all of us. It's you explaining physics to me, the person who it鈥檚 also a favorite subject.
Sam Jones: Yeah, exactly. Okay. So how does a rainbow form? We have to start with the basics because if you'd asked me to explain this to you in detail, I would not have been able to. I was like, there's light, it passes through water, things happen.
Deboki Chakravarti: Refraction, maybe.
Sam Jones: Yeah, you got part of that. Yes, absolutely.
Deboki Chakravarti: Don't ask me how, but I know that word is involved.
Sam Jones: Yes. Okay. So rainbows are the result of sunlight refracting and reflecting through raindrops. Refraction is when light bends as it passes through a material and reflection is when light bounces off a surface. So sunlight is composed of lots of different colored wavelengths that combine to make white light. When that sunlight hits the front of a water droplet, those different wavelengths will bend at different angles, so they will refract, that is refraction. The water droplet acts like a prism that separates the white light into the ROYGBIV colors for those of you who use the ROYGBIV acronym. But yeah, red, orange, yellow, green, blue, indigo, violet, which is the only way that I can ever remember the order of the colors on a rainbow. So then this newly separated light then hits the back of the water droplet, which reflects it back toward the general direction of the incoming light. Then the light refracts again as it leaves the droplet, and that is the light that we see in the rainbow. So it's a combo of refraction, reflection, refraction. We see it.
Deboki Chakravarti: Awesome.
Sam Jones: And I know that I'm also probably oversimplifying this, but this is the most complex I can think about this at this stage.
Deboki Chakravarti: Right.
Sam Jones: Okay, so because the different colored wavelengths bend at different angles, the colors that we observe will depend on our angle of observation. So when we're seeing all the colors of a rainbow from a fixed point is because seeing lots of reflections from raindrops at varying elevations each contributing to one of the ROYGBIV colors. Then something that Tammi wrote in her Tiny Show and Tell Us was that the more prominent the color red is, the larger the raindrops are. And so Ari looked into this, I looked into it a little bit too, and I think it's not quite that simple.
So the size of the droplet does affect how much of the visible spectrum it can effectively reflect back to us. The smaller the droplet, the less that the red side of the rainbow comes through. So water droplets that are about one to two millimeters in diameter give us this bright complete rainbow. Water droplets with a diameter that's smaller than 0.5 millimeters don't show as much red, and the red is then totally absent in droplets that are smaller than 0.3 millimeters in diameter and then below 0.05 millimeters in diameter, you're in the fog, mist territory and none of the defined colors really have a rainbow. So generally speaking, larger raindrops produce narrower rainbows with intense saturated colors, and the red side of the rainbow really comes through.
Deboki Chakravarti: Interesting.
Sam Jones: Yeah, it's not just that large raindrops look red. It's more complicated than that, but it's really interesting to think about, and I didn't think about how different sizes of raindrops would impact what wavelengths you're seeing or which ones look stronger.
Deboki Chakravarti: Yeah, because it's one of those things where it's hard because it's not like the raindrops are making a red rainbow. It's really the way that we are perceiving the light that's refracting and reflecting and refracting again.
Sam Jones: The second thing that Tammi mentioned was that in a double rainbow, the colors are reversed. So when you see a double rainbow, it's not just the same rainbow stacked on top of each other, you're actually seeing a reverse image for one of them. And so remember, rainbows are formed when white light is refracted and separated through a raindrop and then reflected back to us. Some of that reflected light can be reflected a second time within the raindrop before passing through.
Deboki Chakravarti: These raindrops need to chill.
Sam Jones: I know.
Deboki Chakravarti: Or the light needs to chill.
Sam Jones: I know. So that is the light that we observe as a double rainbow. So it's basically a mirror image of the primary rainbow, which is why the colors are reversed. So the second rainbow tends to be larger and fainter, so that's why they can be harder to see, which is so cool. I had no idea, and I obviously hadn't noticed this before because I'm oblivious and I didn't ever look at a double rainbow and go, that's interesting. It looks like the colors are reversed in the other rainbow.
Deboki Chakravarti: Yep. Wowee.
Sam Jones: Yeah. So this was fascinating.
Deboki Chakravarti: Yeah. I'm going to be on the lookout now for the double rainbow.
Sam Jones: Yeah, so that's enough physics for this week.
Deboki Chakravarti: Well, fantastic job. Thank you. That was very helpful. So Sam, I'm here with something sent to us from listener Michai who wrote to us with a preprint from his lab, which studies Robertsonian chromosomes, which are really mysterious but also important for human health. So I was excited to dive into it, but first let's start with actually just what are chromosomes? So chromosomes are structures that store DNA in plant and animal cells, and they include the DNA themselves, but they also have things like histones, which are proteins that keep DNA packaged in a particular way so that it's available for a transcription or replication. And humans have 23 pairs of chromosomes and all of our cells except the ones that we use for reproduction, like the sperm and egg cells.
And so what does a chromosome actually look like? If you've seen a picture, you've probably seen the blobby X shape, and that's not actually a singular chromosome. That's actually the copies of a chromosome connected together, which I didn't realize. I think I had just thought, oh yeah, a chromosome X shape, but they're actually what are called sister chromatids. So in general, each chromosome has two arms that are connected by a structure called the centromere. And so to be ready for cell division, the cell makes a copy of their chromosomes. And those are the two identical copies that are connected together. Again, they're called sister chromatids. They're connected at the centromere, and that's what makes that X structure and the centromere is what helps the cells move that chromosome around during cell division.
And we should note that the centromere, it has center ish kind of in the name. It sounds like it's central, but it's not really. It could actually be kind of far off center so that one arm of the chromosome is shorter than the other end. And so what are Robertsonian chromosomes and how do they actually form?听
So Robertsonian chromosomes are also called ROBs, which I just think is great. We should just call everything ROBs, and they're what happens when two chromosomes whose centromeres are really far off center actually get fused, and this makes a chromosome that's a lot longer than the original chromosome, but also might be missing part or all of the short arms from the original chromosome. And it can also have two centromeres. And these were first identified by a scientist named William Rees Brebner Robertson, who found them in grasshoppers in 1916. But they've since been found in plants, vertebrates and invertebrates, and they are in humans, and they're also heritable.
They can also come with potential health issues like infertility, increased incidences of cancer and trisomies. So they've been recognized for a while, but they're also mysterious. How they happened is just not completely well understood. And so the work that Michai wrote to us about is from a preprint. So the work is still undergoing peer review, but what was really interesting was seeing that they were able to actually assemble these ROBs because I think that will give us more insight into how they originate going forward. I think being able to come up with these things in the lab and find ways to study them will make such a huge difference to our understanding.
Sam Jones: Yeah, totally. It's like a really complicated set of work. I think just understanding chromosomes, understanding epigenetic changes as well, which I know is something that this group was looking at too, where we haven't actually really talked about epigenetics on Tiny Matters. That could be an interesting thing to talk about.
Deboki Chakravarti: For sure.
Sam Jones: It's a fascinating, very complicated field, but essentially things that are influencing whether or not certain genes are transcribed that are outside of just your standard, things that you would think about in genetics, thinking about histones, thinking about methylation, thinking about stuff that's going to keep DNA tightly wound or not, so that it's open to being transcribed. So anyways, I think this seems like something that will help set the basis for trying to understand how chromosomes evolve and how structural variation occurs, why you're getting these Robertsonian chromosomes.
Deboki Chakravarti: For sure.
Sam Jones: And also present in 1 in 800 humans. That's a lot.
Deboki Chakravarti: Yeah. So yeah, I think it'll be really interesting to see where that research goes. Thanks to Michai and Tammi for submitting to Tiny Show and Tell Us, a bonus episode from Tiny Matters created by the American Chemical 中国365bet中文官网 and produced by Multitude. And a big thank you to science journalist Ariana Remmel, who did the research for this episode.
Sam Jones: You can send us an email to be featured in a future Tiny Show and Tell Us episode at tinymatters@acs.org, or you can fill out the form that's linked in the episode description. We'll see you next time.
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