Introduction to Mendelian Genetics
Why Mendel chose peas
- [Instructor] About a hundred and fifty years ago a man named Gregor Mendel, who was actually a monk, raised about twenty-nine thousand pea plants in his garden. You know peas, right? So he raised so many of them, not in one go, but over a period of seven to eight years. Why was he so obsessed with peas? Well, turns out he was trying to find out how traits get inherited from parents to children. For example, what I mean is, let me get rid of this photo. Suppose, lets say my mom has blue eyes and say my dad has brown eyes. Now the question is, what color eyes would I get? What would be the color of my eyes? Would it be blue, from my mom? Or would it be brown from my dad? Or would it be a kind of a mix between brown and blue? So kind of like a brownish-blue eye? Similarly, what about my hair? Would I get straight hair from my mom? Or would I get, would I get curly hair from my dad? Or, again, would it be some kind of a mix? Like, you know, straighty, curly, wavy hair. So you see, Mendel wanted to know exactly how traits gets past on from the parents to the children. And so for that he said let's do experiments. Now of course you can't experiment on humans, that's unethical. And this is why Mendel first started with mice. He thought he would take mice with different characters and make them mate, look at their offsprings, and see if some pattern is there. But that didn't work out. Then he did the same thing with honeybees. That didn't work out as well. The problem is, you can't control when animals mate, right? You can't do that. And so this is when eventually Mendel turned towards garden peas. He found the peas were perfect for his experiment. But why peas exactly? Well, let me just write down the reason. This is important, right? This is the main agenda of this video. Why did he take peas? So one of the first important reason why he chose peas because it's a plant. You can control when plants mate. All you have to do is take pod grains from one plant and put it to another. Right? So, he literally, the mating was literally in his hands. So he could control mating, or fertilization. Fer-tee-lize-ation He could control that so that was great. Another important reason for choosing peas especially is tons of peas have a very short life cycle. So they have short life cycle. Peas take only about, uh, three months to grow to their full height. So because of this short time, you can grow a lot of pea plants and that means you can do a lot of experiments or a lot of data. In contrast, an apple tree takes about ten years to grow to it's full length. So apple tree would be the worst, worst candidate if you want to do a lot of experiments. But if you are really wondering why just pea plants? Why not any other plant with short life cycle? Well that's because, and this is the most important reason, pea plants have a lot of characters. So a lot of characters to experiment with. So they had a lot of characters. What do I mean by this? So let me show you. Let me give you an examples of what characters I'm talking about. Let me give you an example of height. Height. Pea plants can either be tall or they can be short. So the tall ones can grow up to five to six feet tall. The short ones will be one and a half to two feet tall. Okay. Another example of the characters that you can see is in the pea shape itself. You can have pea plants which have round peas or the ones which have wrinkled peas. Similarly, you can do the same thing in the color. You can have pea plants which have yellow seeds, the yellow peas. Or you can have the ones which have green peas. Another example, you can have pea plants which have purple flower or you can have pea plants which have white flower. And there are a couple of other characters as well. So, anyways these properties that you can see, we call them characters. Any property which is visible, all these words, they're officially called, technically called, characters. And the different variations you can get in those characters, like tall and short, or round and wrinkled, they are called traits. Traits, okay? So for example, we could say, pea color is a character and it has two traits. We could say it has a yellow trait and it has a green trait. And now, you may be wondering, okay what do you do with all of this? What's the point? The point is, now, what you can do is, maybe you can take a tall pea plant and fertilize it with a short pea plant and see what offspring you get. And you can check how traits gets passed. Or you can take a purple flower plant and cross it with a white flower plant and see what trait is getting passed. Or maybe you take a short plant with yellow peas and cross it with a tall plant with green peas and see then what happens! So, so many different experiments you can do, right? And by the way another important, ah, advantage of peas you can see is that all these characters have just have just two traits. Two contrasting traits. They're tall or short. Yellow or green. Purple or white. Only two traits. But, ah, if you're to take, for example, the human eye color, it can have three traits. You can have brown or blue or you can have green as well. Think about the human hair color. Think about the human hair types. So many different traits. The more traits you have, the more complicated our experiments become. The more difficult it becomes to keep track of them. But if you just have two traits, perfect. And that's why Mendel probably said, for the next seven to eight years, I'm just gonna grow pea plants after pea plants in my garden. And that's why he grew so many pea plants. And if you're wondering, after all this hard work, did he find anything? The answer is yes! He did find a pattern which forms today the basis of genetics. Which is so important that today, Gregor Mendel is called the Father of Genetics. And we'll get to the experiments and all the fun stuff in the future videos. But for now, let's recall what we learned in this video. Can you recall, what are characters and traits? Can you remember, why Mendel chose pea plants? What are the reasons for that? And can you remember, or name three characters of the pea plants and what their traits are? So, great idea to see if you can recall all this. If you have difficulty in any of this, you can go back and revisit the video. If you are fine with this, then I'll see you in the future videos.