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Alleles and genes

IST‑1 (EU)
IST‑1.I (LO)
IST‑1.I.2 (EK)
A gene as a stretch of DNA on a chromosome. Alleles as versions (sequence variants) of a gene.

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  • sneak peak blue style avatar for user Evan Silverman
    How random can the patterns of ATCG be? Is there an infinite amount of randomness, or is there a way that they can be similar? Also can you take into account identical twins and how they are almost clones?
    (18 votes)
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    • piceratops ultimate style avatar for user Robyn Kayla
      The four "letters" A,T, C and G form three-letter "words" (called codons) - Sal's analogy. Continuing on with this analogy, the "words" form "sentences" depending on the way they are arranged, similar to how word order in an actual sentence is important. These "sentences" are proteins, that have a very specific 3D shape depending on the order of the codons used to make the protein (or words to make the sentence). The 3D shape of the protein determines its function. The collection of proteins in an organism determines the organism - different species have different characteristics, due to the different proteins they can produce.
      Just to round the analogy off nicely, we can think of our entire genome as one big instruction manual. The genome is the manual, the proteins are the sentences within the manual, the codons/amino acids are the words within the sentences and the nucleotides (A, T, C and G) are the letters within the words.
      (7 votes)
  • blobby green style avatar for user paige.lynne.martin
    If the genes have different alleles, can the chromosomes still be homologous?
    (7 votes)
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    • leaf green style avatar for user mystick358
      Yes. An "allele" of a gene can be as simple as a single nucleotide difference, or an insertion or deletion of hundred of bases. While the two genes are not necessarily perfect homologs of one another, there's still enough homology across the chromosome for synapsis (the pairing of homologous chromosomes) to occur.
      (10 votes)
  • blobby green style avatar for user Vong Emsamboramy
    Can anyone explain me how do rRNA, tRNA and rRNA work? Thx before.
    (6 votes)
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    • primosaur seed style avatar for user Faizan
      messenger RNA (mRNA) is a large family of RNA molecules that convey genetic information from DNA to the ribosome, where they specify the amino acid sequence of the protein products of gene expression.
      Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein. tRNAs function at specific sites in the ribosome during translation, which is a process that synthesizes a protein from an mRNA molecule.
      Ribosomal ribonucleic acid (rRNA) is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein by weight, or 3/5 of ribosome mass.
      (9 votes)
  • leaf green style avatar for user amna ahmwd
    difference between gene and alelle?
    (4 votes)
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  • female robot grace style avatar for user Gabby Merritt
    If my mom has dark brown eyes and my dad has blue eyes, how did my brother end up with Blue Eyes and his older sister end up with a green eye and a hazel eye? lol
    (4 votes)
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    • blobby blue style avatar for user Rey
      Your mother must be heterozygous for eye color ("Ee") and your father recessive homozygous (recessive phenotypes must have recessive homozygous genotypes, "ee") The cross is Ee x ee
      resulting in Ee, Ee, ee, ee where you had 50% prob of having blue eyes and 50% brown eyes when you were conceived, the same goes for your brother. Some traits have co-dominance (both recessive and domiant traits are present, such as with spotted fur on dogs or multi color eyes) or incomplete domiance (the recessive and domiant "blend" such as with a red flower and a white flower creating a pink flower). Your brother's sister must have be recessive green in one eye and have co-domiance with green and brown to have a hazel eye.My information may not be correct so I recommend doing some more studying/research on classical genetics!
      (7 votes)
  • duskpin ultimate style avatar for user Anjali Joseph
    why do people not have black eyes?
    (2 votes)
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    • duskpin ultimate style avatar for user Aiyanna :)
      Black eyes do not exist actually. "Black" eyes are really just very dark brown eyes with lots of melanin in the three layers of the iris. The only other case of "black" eyes are those with aniridia (absence of an iris), as your pupil is just a black hole.
      (8 votes)
  • blobby green style avatar for user Sahithi Chowdary
    how many amino acids may a single protein has
    (3 votes)
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  • duskpin sapling style avatar for user karma frazier
    so is gene like traits?
    (2 votes)
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  • duskpin tree style avatar for user VikingTheDude
    At , Sal says something about "pre-messenger RNA" and how we could lose some sections of it. Is he referring to hnRNA? If he is, how does the "losing sections of it" part work? I didn't really get it in school.
    (2 votes)
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  • piceratops seed style avatar for user Ty  Hanrahan
    can a recessive trait only be heterozygous?
    (1 vote)
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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.