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Alleles and genes

Genes and alleles are key players in heredity. Genes are sections of DNA that code for specific proteins or functional RNA. Alleles, on the other hand, are different versions of the same gene. They can lead to variations in traits like eye color. Understanding these differences is crucial to studying inheritance patterns. Created by Sal Khan.

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Video transcript

- What I hope to do in this video is hopefully give you some clarity on terms you might hear used in a fairly related way and those are the terms Gene and Allele. Gene versus Allele. So let's do a little bit of review. Let's just reorient ourselves in the world of DNA and RNA. Let's say that this, this yellow squiggly line is a length of, I don't know, say my DNA, and let's say this little light section right over here, that's if we were to zoom in, and we've represented the various base pairs. And the sequence of base pairs is really the information content in DNA, and here I've just kind of drawn it as a, as a ladder. We know that the real structure of DNA is a is kind of this twisted ladder, this double helix. Now if we talk about this whole yellow squiggly line, and it could be even a section of a longer yellow squiggly line, this could code for multiple for multiple things, especially multiple proteins. So different regions of this could code for different proteins. So for example, this section right over here could be part of this region that I'm highlighting in blue that codes for a specific protein, and so we would call this a Gene. We would call this a Gene. This might be a protein that is involved in, I don't know, I'll make something up. It's a protein that evolved, that's involved in the immune system. Maybe, maybe this stretch, let me do it in different color. Maybe this stretch of DNA right over here, this stretch of DNA maybe it's a longer stretch of DNA. Maybe it codes, it codes for a protein that's used-- Maybe it's a protein that helps regulate DNA replication. Maybe over here is another we encode for another protein that maybe, maybe it in some ways affects, affects the pigmentation of your skin, or the pigmentation of your eyes, and so you these stretches of DNA that code for specific things. And actually it doesn't have to just be even for a protein. We are, we always talked about even if you do code for a protein you go from the DNA to messenger RNA, to messenger RNA and actually go to pre-messenger RNA. That gets processed so you could actually lose some sections of it, but you go to messenger RNA and then that messenger RNA, every three of these base pairs is a Codon. Let me, so let's say that's one codon. One, two, three, that's another codon. One, two, three, each of those-- Maybe I'll draw them next to each other. Each of of them codes for an amino acid that is kind of connected together to form, connected together to form a protein. So that's one amino acid right over there. This could be another amino acid right over there. We can keep going on and on and on and on. You could have another Amino Acid right over here, and then they all bond to each other and they're brought actually to the mRNA from a, by a functional RNA group. And so there are functional things other than proteins that this could code for. Like tRNA, tRNA which is really helping to transport the appropriate Amino Acids to the mRNA in the Ribosomes so that you can construct these proteins. So you can have tRNA and we've seen this before in previous videos. It's this little squiggly line, matches up the the appropriate Codon, and then puts that Amino Acid in place. You also have things like Ribosomal RNA that make up the structure of the actual Ribosomes. So RNA doesn't have to only play this kind of in between messenger function. It actually can play a functional or a structural role. In fact there are theories that the earliest life, the most primitive life was nothing but self replicating RNA and then the systems became more, and more, and more complicated and complex until eventually you end up with things like redwood trees and hippopotami. Hippopotamuses, hippopotami whatever. Elephants, but whatever else, but it all started with potentially self replicating RNA. Some people say it might be some type of proteins are able to replicate, who knows, but RNA is definitely, is definitely an interesting character in this. So you go from Gene to RNA, that's transcription, and then RNA to protein, to protein that is translation but sometimes you just stop at the RNA, and the RNA by itself plays a function. That's functional RNA. So each of these Genes they can code for a type of protein or even a functional RNA. That's what a Gene is. Now what about an Allele? When the Allele is a specific variation of the Gene. So for example, let's say that you look at the at the same stretch of DNA. Let's say this is my DNA and if I were to take your DNA out and if were to look on the same chromosome at the same region. We're both human beings and we have for the most part very similar DNA. So this is-- Actually let me straighten it out. So, let's say this is my DNA, a section of my DNA, and let's say this right over here, this in white is a section of your DNA, and so if we look at that Gene, that blue Gene, that's that on my DNA. Now if we look at that and this is the blue Gene, this is the blue Gene on your DNA. Now we're both human beings and most of our genetic material is fairly similar, but we might have variations in how this Gene is coded. For example, you might have or I might have a let's say, I have a an Adenine right there, but right at that exact spot you might have a different base. You might have a, I don't know, you might have a, you might have-- Actually let me just-- You might have a Thymine right over there. So it's encoding for a protein, or you know, functional RNA that's playing the same role. Maybe it has a role in the immune system or role in your skin color or role in how your brain develops, but there's a variation. There's a variation in how it's coded. Now some of these variations which could arise through mutations, it might not have any impact in the function of the eventual protein that gets constructed. You might just have a different Amino Acid sometimes. In fact, you might not even have a different Amino Acid because many times you have two Codons coding for the same Amino Acid, but even in a case you might have one different Amino Acid in a protein that has 4,000 Amino Acids it doesn't change how that protein acts or how it functions. Or sometimes it might. It might change how that protein functions. It might change how that protein regulates other things and whoever knows whatever else, and so you could imagine that you have Genes. This Gene right over here. Maybe it has a role in eye color, and because of this variation or because of other variations that show up in both cases they code for the protein that say regulates eye color, or regulates the amount of pigment you have, but because your variation right over here might lead or help lead-- And these things are very complex, it's very seldom do you have a gene just for this, but this might make you-- especially if you have a Gene like this from both of your parents, maybe this one would go for blue eyes. Blue eyes, it somehow helps produce blue eyes. While this, while mine somehow helps produce brown eyes. And obviously I'd want to think about which variant of this Gene that I get from my mother, and the variant of this Gene that I get from my father. We all have two copies in our regular somatic cells and our body cells. We have except for-- If we think about the, xx and the xy chromosomes, the sex determining chromosomes, on all the other chromosomes we have two copies of the same Genes. We just have two-- It's just they're different variants. One variant from your mother and one variant from your father, or you could say that they are different Alleles. So Alleles are just different variants. So these are two different Alleles. They code, they're the same Gene. They're the Gene that somehow deals with eye color, but they're different variations for that Gene. So the Gene you're speaking generally to that region of DNA. That region of the DNA strand that codes for some functional molecule, usually protein but it could be RNA. While the Allele is that specific variation. That flavor of that Gene. Hopefully that helps.