• 2 months ago
Transcript
00:00Remove swab from collection receptacle, and gently scrape inside of cheek with a spinning
00:11motion.
00:12I don't know what you expect to find out.
00:20Trust me, you're not a Romanov.
00:24Dear Rita and Moby, what does it mean when someone says, it's in my jeans?
00:30I'm Barbara.
00:31Well, you've probably noticed that family members often resemble each other.
00:37The similarities can be physical, like hair color, or personality stuff, like a goofy
00:43sense of humor.
00:45Some of these traits, or qualities, can be explained by the way we're raised.
00:50But other similarities run deeper.
00:53They're written into instructions within ourselves.
00:57And these instructions are inherited, passed on from parents to children.
01:03That's what people mean when they say, it's in my jeans.
01:07But even before scientists discovered jeans, people knew that some traits were inherited.
01:15Ancient farmers even found a way to influence the process.
01:20Like if they wanted to grow larger fruit, they'd take two plants with the biggest fruit
01:26and breed them.
01:28Their young, or offspring, would be more likely to have those traits too.
01:34Keep breeding plants with the biggest fruit, and the size increases in the whole crop.
01:40This practice of choosing which individuals to breed is called artificial selection.
01:47Farmers have been improving crops and livestock with it for thousands of years.
01:53So it's no surprise that the guy who figured out how it really worked was the son of a
01:59farmer.
02:01His name was Gregor Mendel, and he chose to study pea plants.
02:06They were easy to grow and breed, and had lots of different traits he could observe.
02:12In the mid-1800s, he bred thousands of pea plants and recorded their traits.
02:19Things like height, pod shape, and flower color.
02:23At the time, it was thought that inheritance worked by blending traits from both parents.
02:30Like if a white-flowering pea bred with a purple one, the offspring would be light purple.
02:37But Mendel found that in pea plants, traits didn't mix like paint, they stayed separate.
02:43When he bred plants with white and purple flowers, their offspring's flowers weren't
02:49light purple.
02:50They were either white or purple, the same pattern held for other features he studied.
02:57The offspring would have the same trait as one parent, not a mix of both.
03:04To Mendel, that meant traits must be passed down in separate units.
03:11He called these units factors, and believed they were stored in cells.
03:17It was a revolutionary idea, maybe too revolutionary.
03:22Other scientists ignored it for decades.
03:25Nope, Mendel was definitely onto something.
03:30Turns out, every cell in an organism has the same number of these tiny structures called
03:36chromosomes.
03:38Except for reproductive cells, they only have half as many.
03:43When reproductive cells from two parents fuse to create offspring, two cells become one.
03:51But the chromosomes don't fuse, they stay separate from one another.
03:56So the offspring ends up with the same number of chromosomes as its parents.
04:02It's just like what Mendel described, separate units inherited from each parent.
04:08Mendel's factors are what we now know as genes.
04:12They're located in chromosomes, and each one carries instructions for a trait.
04:20Well, chromosomes are mainly made of a substance called DNA.
04:25It holds the secret to genes, and to life on Earth.
04:30Hidden within DNA's ladder-like structure is a code that cells can read.
04:36The rungs of the ladder are made of four different building blocks.
04:40You can think of them as letters in a very simple language.
04:45String enough of them together, and they can spell out the instructions for building and
04:50operating an organism.
04:53That's all a gene is, the instructions for a specific trait written in DNA.
05:01A lot of the code has to do with making proteins.
05:05These molecules are like the construction equipment for life.
05:10They can be built to do just about anything, from making a plant grow taller to giving
05:16its flowers a certain color.
05:19Genes control these traits by telling cells how to build different proteins.
05:24So those factors that Mendel first imagined are located on strands of DNA, which are bundled
05:31into chromosomes, which get passed from parents to their offspring.
05:38Well, that's if everything goes right.
05:42Every time genes get copied, like when a cell divides in two, there's a chance of mutation.
05:49That's a change to DNA's code, kind of like a typo in a set of instructions.
05:56Mutations can mess up a gene's instructions for building a protein.
06:00Usually it's not a big deal.
06:02It's like when you can still make out a misspelled word.
06:06But sometimes the mistake changes the meaning of the word.
06:11When this kind of mutation happens, cells function differently from how they're supposed
06:16to, which can change traits in all kinds of ways.
06:21That's usually not good for the organism.
06:24A lot of diseases are caused by a genetic error that gets passed down in reproductive
06:30cells, like hemophilia, a dangerous condition that prevents the blood from clotting.
06:37But occasionally a mutation turns out to be beneficial.
06:42Like say a mutation in a fish's DNA gives it better camouflage.
06:48It'll be better at hiding from all the predators that want to eat it.
06:53And if it survives, it may pass that same trait on to its offspring.
06:59This process, called natural selection, is how useful traits spread in nature.
07:06But that process can take millions of years.
07:11Like I said before, ancient farmers used artificial selection to speed up the process.
07:17And today, humans have more control over genes than ever.
07:24Scientists can now change DNA by editing its code directly.
07:29That could give us the power to cure genetic diseases and make all kinds of other changes.
07:36While Mendel's pea plants were easy, a single gene caused a single trait.
07:45But the relationship between genes and traits isn't always so straightforward.
07:50One trait can be affected by many genes.
07:54And one gene can affect many traits.
07:57Plus, whatever your genes are, behavioral stuff like nutrition and exercise can affect how things turn out.
08:04All of which means it's really hard to predict the effects of editing DNA.
08:11We have a lot of thinking to do before we start messing with human genes.
08:17Whoa! Same day service!
08:21Congratulations! You are now the proud owner of your own pair of genetically tailored genes.
08:31Wear them in good health.
08:34I gotta say, they are flattering.