Transcription
Hi everybody. Sorry, my internet is messing around with me, and I'm living in a new house. So I'm trying to get my internet to work nicely, hence all the moving boxes and stuff behind me, everybody. But I know you've been waiting for me to appear. I am here. Um, and so I'm just going to give you a hot second to join the live. Um, and to let anybody that you might know join the live as well. Um, we're going to dive into paper two, do as much as we possibly can in this session together. Um, just as we wait for some more people to join.
I think that we must anticipate tomorrow's exam being a little more technical, everybody. What does that mean? I don't think it's necessarily going to be harder, like paper one was easy and paper two is going to be hard. What I mean by that is I think you must prepare yourself to explain yourself more. We always see in genetics that um matriculants struggle to explain their reasons why they chose what they chose. For example, um, you don't know why parents are in a certain allele. Like, let's say the parent is heterozygous, and then the next question says, "Explain how you know that they're heterozygous." So we're going to see a lot of that probably tomorrow, and I need you guys to be um ready to explain yourself on that. Um, and what we're going to cover today is I'm going to cover what I think you don't do enough of. As I did in the previous live lesson, I think that that's the best way to prepare for an exam is to give you what I think you overlook a lot. Um, we're going to do some past paper questions. I'm going to do a pedigree diagram. I'm going to do an investigation question based off of evolution. Um, we're going to do a human evolution question. I'm going to do some meiosis and some DNA.
And so, I'm not going to chitchat for too long. What I am going to do is I'm just going to um join my whiteboard. And so while I just wait for that to load, um, I'm going to then dive into that. And just remember everybody, you can put questions up in the chat. I will have a look at the chat just now um and try and answer as many questions when we take little breaks in between sessions and sections. Um, I also just want to warn you that I also do anticipate paper two um not having a memo that is going to be very flexible. So, you have to give a good, strong, perfect answer. Um, and I'm going to elaborate a bit more once I have jumped into my whiteboard. So, let me share my screen with you everyone so that we can get this thing going.
Okay. So, um, let's start off everybody with what I want to call things that we get wrong very, very often in the Oh, sorry. I thought there was an insect on me. It was a leaf. Anyway, um, I'm going to do things that we often get very, very wrong or that we make mistakes on. Um, and I'm going to start off with DNA and I'm going to go very, very quickly through DNA. Um, okay, so first things first, things that we get wrong in DNA all the time is when we are asked to identify uh the structures. So, just to elaborate, when we look at the structure of DNA, this is the basic structure. We have the phosphate at the back, we have the sugar, and then we have the nitrogenous base. Now, for now, everyone is pretty good at this, and we know that adenine joins with thymine and guanine joins with cytosine. So, we we know those basics and we're really good at that. But this is where a lot of matriculants make mistakes in the name of the sugar. So, the name of the sugar in DNA is deoxyribose, but in RNA, it's just ribose. So, if you didn't know that, please make a note of that. It is something that a lot of matriculants get wrong a lot. Um, and so please just make a note of that, especially if they ask you tomorrow to do any tabulating. Um, they ask you to do a table um in this last exam, and you also drew a bar graph. I think it was a bar graph. Um, they probably will ask you to draw something else in this exam as well. So, you need to be prepared to do another drawing of some kind. Maybe you might just have to draw something as simple as this. I think maybe they're going to ask you to draw a phase of meiosis or chromosomes, just the chromosomes like what they look like in the phase they've given you. So, they'll give you a phase, they'll have the chromosomes, and you need to draw what the chromosomes will look like, like in future. But I'll get to that when I get to meiosis. So, just let's remember this basic structure, the differences between the sugars. Um, another one that I think that a lot of people don't know is what do we call this structure over here together? The phosphate and the sugar. A lot of us don't know that that is the sugar-phosphate backbone. Um, that's something that we forget a lot.
Another thing that we forget about in DNA, just going to move my page up here, is I think we all know the shape of DNA, which is a double helix, but we forget about the proteins that hold DNA together. Another word we forget is a histone. That is a protein that holds the whole thing together. Um, and then I get a lot of questions about, "Do we need to know the enzymes, the specific names of the enzymes in DNA?" No, you can just call them the enzymes. You can call them uh, if you really want to call them DNA polymerase if you really want to, but you can just call them the enzymes that you need for translation and transcription. Um, speaking of translation, transcription, in my my prediction video, I talked about tRNA, and I think it's because I feel like we're not good at tRNA. So, I'm just going to go over tRNA really quickly. This is a tRNA molecule. At the back, we have an amino acid, and at the bottom, we have the anticodon, which remember is complementary to the codon on the mRNA. Um, and so, for example, if the codon or sorry, the anticodon is UUC, then the mRNA that would be sitting below it would be something like AAG. Remember, there is no thymine in um RNA. So, just keep that in mind. Um, they like to ask tRNA, and they like to ask um mutations as well. We've kind of spoken about that, and I I we always see it. I always it's like I can close my eyes and and know that that's going to be in the exam. Like, I can actually just imagine flipping the page over and seeing question 2.1 being a DNA question, and then 2.2 two being a mutation question which follows, which has like a codon table, and then and then errors in the codon, like like I I already know what's going to be there. Um, they they have to ask it because you they you need depth of knowledge in this. Um, I spoke about also um potentially what uh in the prediction video what you might overlook, and remember, I don't want you to forget to look through DNA replication, please, because we forget about it. We just focus on translation, transcription. So, don't forget to go over that as well. And then also, most importantly, when does all of this occur? It occurs in interphase. Um, they love to ask that question as well. When does it occur? In interphase. Um, what else can I say about DNA other than it's probably going to be the easiest part of your whole exam? You'll be very lucky tomorrow if they ask you to um explain translation or explain transcription for like five or six marks. Please remember to only use the guideline for that. Don't use anything else. Don't use um any other um explanations. Uh, if you're using my cheat sheet explanation, that's okay because I've actually taken that from the guideline and I've I've written it as a metric marker, so I know exactly what they want. But if we're just working from a textbook, um, I wouldn't use what's out of your textbook, basically. Thank you so much, Luga, for the tip. I really appreciate that. Um, okay. So, I'm just going to pause for uh two seconds and just have a quick look at your questions about DNA. The first one I'm seeing is, "Do we need to know purines and pyrimidines?" The answer is yes. You would need to know uh thymine, guanine, cytosine, and adenine. Which group do they fall into? Um, let me, I'm just sorry, I'm scrolling backwards to have a look. Um, you must Oh, this is actually such a good one. Okay, matriculants, I forgot about this one. So, I'm reading someone's question. It's making me think of it. I think it's Brianna's question. She speaks about the shape, the importance of the shape, and must we stipulate it's a molecule? I love this. Okay, a lot of matriculants don't know this because I guess their teachers don't emphasize it, but you have to refer to DNA as a molecule. So, it's a DNA molecule. It's important. And I don't want to get into a lot of detail why because it it'll we'll be be forever talking about why it's important. I just want you tomorrow to always refer to DNA as a DNA molecule, and that is referring to the whole thing. So, if I just refer to my picture, this is a molecule, the whole thing. This is a strand, which means one side. So, there's strand one and there's strand two. Please don't call it molecule one and molecule two. That's what I'm basically saying. You call them a strand one, strand two. The whole thing together is a molecule. Okay, lovely. Um, I'm just popping through some of the other questions. If you do want to watch this live later, you can. You can rewind it. It It will be uploaded when we're done as well.
Okay. Um, Shayon wants to ask, "Is there, excuse me, a specific difference between DNA replication and transcription that we should know?" Um, well, yes, there are specific differences. Um, DNA replication, you get two strands, whereas uh, so you're making two identical strands, whereas the other whereas in transcription, it's it's it's a single strand and it's not identical. Um, what else can I say? Um, one is double helix, which would be trans, which would be DNA replication, and then the other would just be a strand, a straight strand because it's mRNA. So, mRNA and DRNA would, DNA would be technically another difference. Um, and then, oh, another difference would be the purpose. So, DNA replication, what is the purpose if that's what they want as a difference? Uh, the purpose would be for cellular division or repairing and replacing cells, whereas um transcription is for protein synthesis. So, that's also a physical and then a functional difference that we should know. Okay, I think I'm going to move on because everything will kind of start filtering into themselves. And I see all your questions about other things like um gel electrophoresis and karyotypes. Again, I actually said this in my prediction video. I think there's going to be a karyotype and a fingerprint tomorrow, but in two different ways. So, there's always going to be some kind of like gel electrophoresis where it's like, "Who is the dad?" or "Who is the murderer?" And everybody, it's pretty straightforward. If you get a gel electrophoresis sheet like this, remember you are just trying to identify all the pieces that line up with the individual, and whoever has the most pieces. I need to add more now because I haven't actually planned it out. Well, oh wait, no, there is another one over there. Whoever has the most pieces ends up being the father. Uh, or in this case, if we're looking for a murder victim, or we're looking for a um someone who's like committed a crime, I would say that you're looking for the person who shares the most between it. So, if this is the sample, then this one here would be the, let's call it the murderer. Um, and that is because we've got 1, 2, 3, 4 in common, and the others only have three. Right.
Now, um, when you're explaining yourself, and this is what I'm trying to get at today, you are going to lose marks tomorrow, not because you can't do this. You can tell who's the dad. You can tell who's the murderer. You can tell me if it's a karyotype, you know, and you've got the chromosomes and there's an extra number 21, they've got it, they've got Down syndrome. I know you guys can tell me that. What you can't tell me is why. So, let me explain. If they're asking for paternity with a gel electrophoresis, so like a DNA profile, you need to explain that you get 50% from mom and you're getting 50% from dad. So, you got 50% of those markers from mom and 50 from dad. If it was a murder, then your reasoning is there must be a 100% match. And that's the first point about explaining yourself and being able to explain yourself about why you chose what you chose. Likewise, in a karyotype, if they ask you, let's say the karyotype has a set of chromosomes that look like this, and they say, "What sex is this person?" You would go, "Oh, well, that's an X and that's a Y because it's a well, I'm not going to say why. You know that. Okay, that's a boy. Okay, so it's male." Then they ask you why. A lot of matriculants don't know why. They'll just go, "I just know it is." And so that's what I'm trying to get at is for tomorrow you need to be really good at explaining yourself. And ultimately, it's because of the size, right? The X chromosome is a large chromosome. It's the biggest chromosome. And the Y chromosome is much smaller. I don't know if you know this, but the X and Y chromosome are not actually homologous pairs. They don't actually touch each other. They never do crossing over. And that's because they're not a homologous pair. They are not the same size and they don't carry the same genes, so they can't cross over. If you're a girl and you have two X's, then yes, you can have crossing over occur.
All right, which is a great segue everybody to meiosis. Now, again, I don't think matriculants study enough meiosis. I think that you think it's going to be 20 marks, done and dusted, easy peasy. They're going to make you label something and then it's over with. No. So, um, let me explain what I think is going to be a problem. So, there are always two danger phases that matriculants get wrong, and it all has to do with the chromosomes. You don't know what the chromosomes are actually doing. So, let me explain. The first phase is going to be my meiosis, and specifically, this is going to be metaphase two, and I'll actually, and I'm going out of order here, but I will draw metaphase one below. Okay, it's metaphase one. We put our here we go. Okay. Quick sketch. Okay. Okay. And this is metaphase one. Okay. So, number one, why uh, sorry, this little popup box. Let's just close it. Um, why do matriculants get this wrong? Well, congratulations. You all identify it as metaphase. Yay. But we don't identify it correctly as one or two. And then the follow-on question is always going to be, "How do you know it's metaphase one? How do you know it's metaphase two?" Okay, I'm going to tell you. It all has to do with the number of chromosomes and how they are arranged. So, whenever we see a set of chromosomes like we see over here, where they are singular, in other words, it's a single chromosome versus over here, we have a pair. That is going to give us an indication as to whether or not we are in meiosis one or meiosis two. So, in meiosis one, you have homologous pairs. Okay. But in meiosis two, you just have a homologous chromosome. That's what you would call that. If you wanted to, you could say that in meiosis one, there's one chromosome that's double-stranded, whereas in meiosis one, there's two chromosomes that are double-stranded. But I don't like using that. And and your matric markers won't like that either. They won't like that because they don't know if you understand what a homologous pair is. So, the pair is referring to both of these, whereas the homologous chromosome is just referring to the one. Now, ma'am, why does this matter? Well, the second phase that matriculants always get wrong and can't explain themselves, like they did last year. Matriculants couldn't explain anaphase last year at all. And I'm very, it's very sad when you mark all those papers and you see thousands of children not explain it correctly. Um, and they lose out on very easy marks. So, if we're going to draw anaphase, I know I'm drawing the second one first, but it doesn't really matter, guys. If you're good at meiosis, what I'm doing here now shouldn't confuse you. The fact that I'm drawing them not in order. Okay, this is anaphase two. This is anaphase one. So, why do matriculants get this phase wrong as well? So, number one, you get it wrong because you're not looking at the chromosomes. Remember the chromosomes, as you can see here, have splits, right? So, it's a single chromosome like that, versus here, you still have a double-stranded structure. So, in anaphase one, you should still have a double-stranded chromosome, or you could call it a homologous chromosome, whereas in one, sorry, in two, you now have a single. But how do you actually explain that? So, let me tell you what wording you you need to use to describe them separating from each other. So, let's go over that. Let's start off with anaphase one. So, I'm going to start at the bottom here. When you talk about anaphase one, you're going to say something along the lines of homologous, oh no, not chromosomes. Homologous pairs are pulled to opposite poles. And you can also say like spindle fibers shorten. Okay, I just want you to know that last year this got a tick and this got a tick. And so if you didn't mention that it's a homologous pair and you just said the chromosomes are moving to opposite poles, you wouldn't have gotten the mark either. So, like I said at the beginning of the live, you being very specific tomorrow is the most important thing you could possibly do. Okay, be very specific. So, in anaphase one, it's the homologous pairs that are pulled to opposite poles because the fibers are shortening. But in anaphase two, what is happening? Okay, listen carefully to the difference. We're going to say chromatids move to opposite poles. And again, you can mention that these spindle fibers shorten. Important tick on the chromatids. Important opposite poles. It must always be opposite. Okay. If you were going to ever explain nondisjunction in any of these, because remember nondisjunction occurs in either anaphase one or anaphase two. So, if you were ever going to explain it, just remember that you need to say that either the chromatid or the pair, so the homologous pair, are pulled to the same pole. Emphasis on the word same. So, if you ever have to explain how nondisjunction occurred, please make sure that you are describing that both of the homologous pair are moving to one um pole or the same pole. Likewise, the chromatids fail to separate and are pulled to the same pole. We need to do that every single time, everybody. That is really important. Nondisjunction always makes an appearance because it's a great explanation question that examiners like to ask. Okay. Um, before I go any further, the only other thing matriculants get wrong in meiosis is um very basic things, which surprises a lot of lot of matriculants that you think you get this wrong, but a lot of matriculants get this wrong is just the basics around the structure of the chromosome. So, remember, this is the chromatid, this is the centromere, and this is a chromosome. Okay. Other things that matriculants get wrong linked to the structures and this kind of thing is crossing over. So, I need you all to know when crossing over takes place, which we should all know, it only takes place in prophase one. Hey, only in one, doesn't take place in prophase two. So, don't ever use that as a reason for why you know it's prophase two. That's it's not prophase two because they're crossing over because they don't cross over, right? Um, so let's talk about this action here of the chromosomes doing crossing over during prophase one. So, first of all, does anybody even know what the movement is called? It's another one matriculants don't study very often. What is it called when the chromosomes move together and touch? It's called synapsis. Where they touch, chiasma or chiasmata, it it's fine. It doesn't matter which one you want to use. You can say chiasma or chiasmata. It just means one or many. It doesn't matter. Um, what else do we want to remember? And then what does it form? Okay. Now, the word bivalent has been removed from the exam guideline. If you use it, I would say it's a bad idea. I wouldn't call anything a bivalent anymore. I would just simply call these a homologous pair that are touching. That's it. You don't need to call them anything else. But when I say, "What do they form?" what I mean is when you have a a crossing over that's occurred and now you have chromosomes that kind of look like this. Now, what do you call those? A lot of matriculants don't know. We call those a recombinant chromosome. Okay? And that's what I wanted to lead into now, everybody, is you might be asked to draw something like this tomorrow. Um, it's either going to be what the chromosomes will look like after touching, and sometimes what they do is they give them like letters like that, you know, like the genetics letters like a big letter and a small letter so that you can um so that you can like follow the letters in your diagram. So, here's my top tips for drawing meiosis diagrams. Number one, always make the heading what they're asking you to make the heading. That sounds like, duh, ma'am, of course. But what I mean is a lot of matriculants don't write what the question asks for. If the question says, "Draw a diagram showing meiosis two," the heading must say, "Diagram showing meiosis two," or "Metaphase two," or "Anaphase two." Or if they ask you for a structure and they say, "Draw structure B," your heading must say, "Diagram showing structure B." Okay. Next. This is the only time in life sciences you're allowed to color things in. So, as I've shaded in over here, please also shade in if they want you to shade in and they want to show where the crossing over has taken place. And then last but not least, you should always provide a minimum of three labels for meiosis uh diagrams. So, you can label the chromosomes, the centromeres, the um cell membrane. Um, maybe if there's no cell membrane in the picture, then you need to label something else, like maybe they've asked you to label the gene location, which is what ma'am has done here with the letter B's and the letter R's. You know, capital B and little R and little B and big B, that kind of thing. There are a number of matric exams that do this and have done this. There's lots of past paper questions. Okay, so that's kind of it for meiosis in terms of revision on it. I'm not going to go into too much detail um because I have a number of questions I want to get to, which I'm going to zoom into now. You can see my whole whiteboard is ready to go. Um, I'm going to look at the chat now for some questions, and we're going to dive into this pedigree question shortly now. Um, I'll make it bigger for you so you can all see it. Oh, this one came from the past paper, the NSC of 2022. Um, and so we will see some kind of pedigree tomorrow. I'm just going to have a quick look at some of the questions and just see if there is anything that I want to answer for you.
Shayen asks, "When is it called a recombinant bivalent and homologous chromosomes?" So, a recombinant is after crossing over. We're not going to use the word bivalent anymore. Technically, that's while they're crossing over. So, while they're touching. So, recombinant is after they've touched. And homologous chromosome, you can use that word before they touch. So, before like if they're just existing, you know, like this and they haven't touched yet, you can call the one chromosome a homologous chromosome. And then a homologous pair is the two together. You can also use the word homologous chromosome when they've aligned on the equator and they're going to pull apart. Um, it's also not wrong to write a recombinant homologous chromosome or something like that. Like, like it's okay to put some of these words together, but to make it simple, recombinant, I'm only ever going to use after they've touched. Um, and you can actually see the recombination, like the little patches of color on them have changed. Um, and I would use homologous chromosome throughout. You can use it throughout, beginning and end. Um, I'm not trying to overcomplicate it as well, everybody. I don't want to overexplain it for everyone out there. Um, the safest words to use would be the homologous pairs and homologous chromosomes. Basically, um, Tanique asks, "What are the structural differences between tRNA and mRNA?" Well, the structural differences would be something like a codon and an anticodon. Um, the other one could be the structural difference in terms of the shape. So, tRNA is kind of like a three-leaf clover, whereas mRNA is a long strand, a straight strand. Um, tRNA carries amino acids, whereas mRNA is the coding for amino acids. That's another difference. Um, you should know about three, I would say, for every everything we've learned together. You should know three differences. Um, Lily wants to know, and this is the last question I'll do for meiosis, "When do we go from calling it a chromatid to a single-stranded chromosome?" Lovely question. Very good question. Um, you are going to go from a chromatid to a single-stranded chromosome. Um, after anaphase one, excuse me, anaphase two, anaphase two, anaphase two, anaphase two. So, before that, you're going to call it a chromatid. So, when they're still attached, so there's still chromatids. And then in anaphase two, you'll say the chromatids pull apart, and now they are single-stranded chromosomes. Okay.
Um, let's move on to this pedigree diagram question. I thought it was a nice one. Um, and I wanted to practice this one because it is a dominant disorder, which we often don't practice enough of in class or school. So, um, it says here that the disorder is caused by a dominant allele, which it tells us, and the disorder damages the arteries supplying blood to the brain. This is our family. Now, um, first things first, a lot of matriculants see female and male and they go, "Oh, this must be a sex-linked cross." Just because it has male and female doesn't mean it's a sex-linked cross, right, matriculants? You've got to look for the um sex chromosomes in the question, and there isn't a sex chromosome. There is just the capital letter R. So, R is dominant, and that means you have the disorder. So, I'll put a little tick, and then the little r is recessive, which means you don't have the disorder. So, if we were to go through this family, which is what I encourage all my matriculants to do, is go through the family tree and fill in everybody you know for certain, and then kind of work your way back and add in everyone who's missing. I know this feels like this takes up a lot of time, but I promise you, you won't make as many mistakes. Okay, so let's go into all of the people who are unaffected. So, if you're an unaffected human, male or female, you won't be colored in, which means that I can go in here and I can quickly give everyone two little r's who is not colored in. Then I look at who is affected. Now, if you're affected, you're colored in, which means you have a minimum of one capital R, a minimum, because remember, this is a dominant disorder, which means um you need only one letter to have it. Remember, it's a dominant disorder. You only need one capital. So, then how do I know what the other letter is? So, we always work our way back. Now, let's start off with finding out what A is. So, we're going to look at their children. Now, the fact that there is a child here, D, that has two small r's, the only way that's possible according to the law of segregation is one of the small r's comes from mom, which means the other one must come from dad. So, we've solved what A is. If we want to do C now, we again can look at the child, which is um two lowercase r's, which means they got one from mom, definitely, and they must have got the other one from dad. If we go over to the other side of the family, we look at E. Now, E is going to be tricky because they have got a capital R, which they got from dad, which means the only other letter they could have got from mom is a little r. Right? We now look at their children. So, H has two small r's, which confirms now that this is definitely possible and true that E is a small r. But now, what is I and J? Well, I and J both got capital R's from their dad, which means mom could only possibly give them a small letter r. So, we've now solved the family tree. But now that we've done that, let's look at the questions and what they expect of us. So, this is an easy one. "How many generations are in this diagram?" Well, we've got one, two, three. So, there are three generations in this diagram. Then it says, "Give the letters of the unaffected males." So, the males that are not colored in, which it looks like there's only one unaffected. So, that's H. He's the only person who's an unaffected male. Then it says, "Give the genotype of individual A," which we have already done. It's big R and little r. And then finally, "Give the letters of individuals not biologically related to A and B." In other words, everybody who's not a child or a grandchild of A and B. So, that would be C is not related to them, and F. So, I'm going to put here C and F. And that's pretty straightforward, isn't it? Now, before you think, "Man, that was easy," just remember this is a very simple level one question. It is from 1.4, which means it's very straightforward, very basic. But I want you to know that um again, one of the mistakes matriculants make is not being able to explain how they know the parents are the letters they are. Um, another thing is how do you explain sex-linked diseases or sex-linked inheritance? And so this is what I teach my matriculants. So, this is my top tip for you tomorrow. If they ever give you a pedigree like this and they want you to explain inheritance, okay? In other words, explain why the baby is this letter or explain why mom and dad are this. Like, what are their letters? There's actually a formula I teach my matriculants. It's also in my cheat sheet as well. And this is how it goes. It's foolproof. It's failure-proof. So, explain the inheritance. If you are going to explain a child, let's say the child is big letter, small letter R, like that, you have to explain how that happened. First of all, you're going to tell me what is dad. So, dad's that. Next one, you're going to tell me what is mom. Mom's that. Okay. Then you're going to tell me what I got from each of them. In other words, I got a big R from dad and I got a little r from mom. And I round that off by saying, therefore, I'm going to tell you what the child is. And the child is big R, little r. That is foolproof, everybody. That is one, two, three, four mark explanation on how to explain the inheritance when it comes to children and their parents. Okay.
Next one that I always love to teach my pupils has to do with sex-linked. Let's say they ask you to explain sex-linked issues or characteristics, right? Sex-linked inheritance. Now, the most common question is, "Why?" I'll write it here. "Why more boys than girls?" Right? That is the classic question they ask in the exam. "Why do more boys have red-green color blindness than girls?" Okay. Well, yet again, you take a similar formula. Okay. You're going to tell me what are boys. You're going to tell me their XY. Okay. Then you're going to tell me what is the disease. It's an X-linked disease. Right? So, if it's red-green color blindness, it's R, and therefore it is recessive. Okay. So, you're going to tell me what are boys. Then you're going to tell me what is the disease. The disease is this recessive. Now, you're going to say, you're going to speak about masking and covering and that kind of thing. You're going to tell me something about how many X's do boys have, and that is one, because they have one. Therefore, if affected, they will have it, "it" being the disorder. Now, I want you to just pause for a second and hear me very clearly on what I'm going to say next. Do you have to explain any girls in this answer? The answer is maybe. If they're asking you to explain why there are more boys than girls, then yes, you could go one more bullet point here to say, um, girls are XX. So, it must be on both, both of the X's, right? So, it must be like this, XR XR. But what happens if they flip it on you, grade 12s, and they say, "Why are girls not as affected as boys?" So, why don't girls experience hemophilia? Why don't girls experience as much red-green color blindness? Right? So, they're not asking about boys, they're asking about the girls. Okay? So, this is where it's important. Uh, small change. This is a small change. All you're going to do is you're going to focus your explanation on this aspect over here. You're going to talk about the girls. You're going to say, "Well, girls are XXX tick." So, it must be on both tick, because this disease is recessive, which is this one up here. The point I'm getting at is you must determine who is the question speaking about. Is the question asking about boys? Just boys, not a comparison to girls, just boys, then the answer must only talk about boys. If it says "more boys than girls," you can talk about both. If it just says "girls," we're only going to talk about girls. We're not going to mention the boy stuff. It's not important. It won't get you any marks. It's a waste of time. And potentially, you might think, "Oh, I've got four out of four because I have so much stuff I've written." But you actually haven't written enough. You've you've written about too many different people. You were only supposed to talk about the girls. So, just remember everybody to do this kind of thing and be able to explain sex-linked and basic inheritance. Okay?
Righty ho. Let us move on to a let's do a human evolution question. This one over here. This one I also took from 2022. This is the supplementary paper. A lot of matriculants don't practice supplementary papers, guys. I don't know why you wouldn't want to practice supplementary papers. They're the most recently written paper, which would be the 2025 one, which you can write if you want to now and you can practice it. Just keep in mind that whatever they ask in the supplementary paper, they're not going to ask again. Now, however, however, I just want you to know, whoever set the supplementary this year in June set this paper too. So, if you want to get a good idea of their thinking and the examiner's style of question, then you should be doing the 2025 paper today so that you can see their style. It doesn't mean that they're going to ask those questions, but it gives you an idea of what kind of language they're looking for, what kind of style of question they're going to ask you tomorrow, that kind of thing. Um, supplementary papers are hard to find, but I'm going to tell you the easiest place to find them, everybody, on the government website. Go to the official official Department of Education website. Type in, don't even have to go on to the website. Just Google um past papers department of education and go to the link, whichever the ones that suggest there. Go to the link that says DBE, Department of Education, and then it says past papers. Click on that, and right there will be the past papers. I'll actually do it in the background now so I can show it to you. Past papers, Department of Education. I'll open the tab now so that you can see it. Let's see. Where is it? Uh, here we go. Okay, you can see my screen. Right, there it is. We're going to go here and look right there. Right at the very top there. 2025 May June NSC examination paper. We click on it. My internet is going to work for us. Maybe it will, maybe it won't, but you get the idea there. It's where it's sitting. There we go. And then they have every single subject, Afrikaans, English, all the languages. And if you scroll all the way down, you get all your subjects. And there's life sciences with the memos. Okay, everyone. So, they're not impossible to find. Let's go back to my whiteboard and let's do this human evolution question because I want to do one more question after this as well. So, let's dive into human evolution. So, before I start, don't forget to go over the out of Africa hypothesis as well. A lot of matriculants don't study it enough. So, I suggest that you make sure that you know it well. Ma'am, what do we need to know in out of Africa? You need to know the out of Africa theory. So, that is where did we find the fossils, and uh, where are the oldest, and where are the youngest? So, please know the names of those fossils um and where, in other words, they were all found here in South Africa or in Africa, only the oldest fossils. Key words: oldest and only. Please put those in your explanations. Oldest and only. Okay. All right. Let's dive into here this question. Now, this one is about the foramen magnum and the palate as well. I do think though, maybe tomorrow they're going to ask you something about the hip bones. So, be prepared for that because it's linked to bipedalism. So, it says, "Diagram A and B show the ventral or the bottom view of two skulls. These are not drawn to scale," which is not really important to us. Now, before I even begin, I would identify who is who. And I definitely know that this is an ape and this is some kind of human. It might not be a human per se, but it's definitely a humanoid. And I already know that that is an ape for many reasons. So, let's actually go through some of the reasons why I know which one is which. First of all, the foramen magnum. Please remember, matriculants, you may only use the words "more forward" when you talk about the foramen magnum. You are not allowed to talk about it being central. The word central is a no. It's a no for me. It's either more forward or more backward. The foramen magnum. The next reason why I know this is an ape versus a human is the canines. These are large. Ours are small and reduced. You can't even see them here. Another reason how I know which one is which is the shape of the palate. So, there's the one shape. There's the other shape. Right? This is a rectangle. This is more of a U shape. Some textbooks say parabolic. That's also okay as well. So, now we have some really good annotations on our diagram. Let's go into our questions. And I often see matriculants don't annotate their diagrams while they do their questions. And again, that's what separates the 60 percenters from the 80 percenters is that if you look at an 80 percenter and a 90 percenter pupil, often they are annotating all over their diagram. But anyway, let's move on. So, number one says, "Which diagram represents the skull of a bipedal organism?" So, we already know that's going to be B. And now this is your shortfall, right? It always asks you, "Give one visible reason for your answer." So, my visible reason is going to be the foramen magnum is more forward. I know that's out of two marks, and you're like, "What would you get two marks for that?" You're getting one for the foramen magnum and you're getting one for its position. Okay, pretty straightforward on that one. Now, it says, "If we move it down a bit," there's our table. "Two visible differences between the upper jaws." That's important. Upper jaws. Upper jaws, everyone. Not the skull. Upper jaws. And that represents trends in human evolution. So, uh, how do you get five marks? So, number one, you always need a heading, right? Number two is you need it to actually look like a table. So, if that is A and that is B, and you're going to give two visible differences. As before, my visible differences would have been the palate shape. So, that would have been the U shape and the rectangle, and then the canines would have been my other one. So, would have been large canine, small canine. You could also say reduced canine. Okay.
I'm just going to pause for a second and read some of your questions. Um, M wants to know, "Do we know do we do we need to know which hominins were bipedal, had prognathism, and other details, or is it more important to know the order of hominids?" So, no, it's not more important to know the order. It's more important to know the structures that those individuals had. So, it's more important to know who had big canines, who had small canines, who had a prognathic jaw, who didn't have a prognathic jaw, who had a large cranium, who didn't have a large cranium, who had a flat face, who had a sloped face. Um, but with that being said, I think you also overstudy that because they often don't ask you individual skulls, you know, like it's very specific. As you can see here, this is not very specific. You just need to know that apes or hominid ancestors look like this. They're more primitive, right? Bigger teeth, longer face. This is a prognathic jaw. You can see this is prognathic. The jaw sticks out in front of the face, versus this is a non-prognathic jaw. It's flat. The teeth are sitting close. So, it's more about seeing the trend and less about knowing individuals. I think a lot of matriculants spend way too much time studying things. Um, "Please tell the difference between a hominid and a hominin." So, a hominid and a hominin. Hominids are referring to all of our direct family, whether it be Australopithecines or Homo habilis. Those are hominids, basically two-legged individuals. Hominins are more specific, and that's specifically the Homo group. And before anyone says they're not going to ask that, they have before. Everyone, they have before. Uh, "What do we call the gap between the canine and the other tooth?" Uh, the gap is called a diastema. That's the gap, everyone. If you didn't know that, now you know. Um, "Which fossils do we know details of?" So, the most important fossil ever, ever, ever, ever. And I'm going to do the last question here, don't worry. The most important fossil is um Lucy. Lucy is our gal. Okay? She's important. She's our Australopithecine. She's the one that if I do a rough sketch, is often like so, like she's missing the bottom part of her her her face, which she is. And um she's the one with like really large canines often and teeth. And that's how we also know that it's her. We know that it's her also because she's got a small cranium. She's got a sloping face. So, she has prognathism. She has a very big eyebrow ridge. So, Lucy is one of the most important ones that we do need to know. Do they ever ask the year they were found in? No, but they ask the country and the person. Um, do we have to know who discovered? Yeah, you do need to know who and where. Um, "10 out of 10 for my drawing." Thank you. But you get the idea, everybody. I think everyone knows which fossil I'm talking about. Okay. So, um, "Are cranial ridges and brow ridges the same?" No. These are eyebrows. Cranial is up here, also known as a sagittal crest. Okay. Brow ridge. Cranial ridge. Okay.
Okay, everyone. I want to do this last question because I don't want to leave it out. But you may remember in paper one, there was a lot of significance questions. There's actually two. Do you remember? There was like, "Explain the significance of this," and "Explain the significance."
Of that. Okay. Um, and I have beef with with people on the internet arguing with me about what the difference is between significance and the word importance. And people are beefing with me, telling me that they are the same thing. Look at me. They are not the same thing. If you answer them the same way, we have a problem, cuz you're probably not going to get it right then.
What does it mean to be significant? I teach my matrix this. It's not about the importance, it's about the outcome. So if you read that word tomorrow, replace it with the word outcome. Explain the outcome of the shape of the spine that is associated with skull B. So skull B is the humanoid, right? The hominin, what we think is a human. Now we're going to explain the significance of that. So what is the shape of the spine? Well, we have two options, right? You could have a C-shape or an S shape. Which one is bipedal and which one is associated with B? S is associated with skull B. So now, so it's not this one. So now what we need to do is explain the significance of the shape of the spine that is associated. So what is the significance of this? The significance, the outcome is this person is bipedal. Therefore, with the S shape, there is even distribution [Music] of weight. You could also say the weight is distributed in the middle of the body. It is not importance. The word significance does not mean importance. So explain the significance means explain the outcome. What is the outcome? The outcome is we are bipedal. Therefore, the S shape then allows us to have an even distribution of our body weight to keep us upright. Okay?
Please everybody, it was the same for for for Friday's paper. If you didn't describe the outcome, I think the one was explain the significance of the size of the arterials, you know, when they got bigger and smaller and thermoregulation. Basically, you you describe the final, the significance of it being open or closed. I can't remember which one it was, but you you you explain the significance of that, not the importance of it. It's not the same thing because importance means it's a positive thing. Not every single thing that is significant is important. Do you see what I'm saying? Like, not everything that's significant is positive. Significant can also be negative. If somebody asks you in this exam on Monday, tomorrow, what is the significance of nondisjunction? It's not important. That's you can't write what's the importance of nondisjunction. It's not important. We don't want nondisjunction. So the significance of something like nondisjunction is the outcome. What is the outcome of nondisjunction? Well, the outcome is you will have a cell with too many chromosomes and another cell with too few, and this would have occurred during anaphase one or anaphase two. So, please substitute the word significance with the outcome. Okay. All right. So, that's pretty straightforward when it comes to some of the things that they might ask you. And I'm going to do one more. Well, I was going to stop the lesson just now, but I'm going to do this last one over here, which is about um natural selection today. And I do think there will be something like this. This was a plant one. I did say in my prediction video that there might be a plant natural selection situation. This one is about resistance to herbicides though. Um, it could be anything though. They're allowed to ask you anything. They also are allowed to ask you the formation of a new species tomorrow. So, be prepared for that. They are allowed to ask you um natural selection when it comes to Lamarck versus Darwin. So, can you compare the two? And I also spoke about this in my prediction video about punctuated equilibrium. Don't forget to go over that and how we use punctuated equilibrium to describe short bursts of change with long bursts of no change. And what kind of population would we see this in? We don't see it everywhere. We only see it in small communities um and in small populations. So micro populations. Okay.
Okay guys, let's go into our last little bit for today and then I'm going to wrap it up in this lesson and just see if there are any physical questions I can answer here. So it says the herbicide glyphosate, that's the herbicide, is used to control weeds in maize fields. The herbicide kills weeds. It can also kill the maize plants. It has been found that some weeds develop resistance to the glyphosate treatment. Scientists carried out an investigation and please highlight this part. It's your aim to determine the development of glyphosate resistance in weeds. The weeds were treated with the same concentration of glyphosate each year from 2009 to 2006 and the percentage of glyphosate resistance in the field was recorded every year and we have that in the table below so far. So good. Nothing too challenging. Number one says, describe the change in glyphosate resistance over time. So, it's out of three. And I know you're probably wondering, well, what must I say for three marks? Like, what would I get? So, I just want you to notice that if you look over time, you will see that it is increasing. So your first mark would go to you speaking about as there is an increase in time, there is an increase oops in resistance. But then to get the third mark, I want you to acknowledge that it remains the same. So you can say here from 2015 to 2016, it remains the same, and that's what gets you your three marks. So don't rush too quickly on those kinds of questions and just think you can say two things. It is for three. So be very careful that you look at the numbers and you actually see, is it actually increasing? Oh no, it's not. This is where it plateaus or it levels off. So that one's easy.
Next one is calculate the percentage increase. I think you did a calculation on Friday. Um, but you must always be prepared to do a um calculation. Remember when we're doing percentage increase or decrease, please remember it is final minus initial over initial times 100. Okay. So what is the initial amount from 2010? That would be 20. And then into 2015, it's 65. Yeah. No. Oh, I put them the wrong way around. Hold on. Let me get my little. Yeah, that is how we calculate percentage increase, right? I'm going to double check percentage increase. I'm going to double check quick sticks because I keep saying it. But I think that's how you do it. Final minus. Is it final minus initial or initial minus final? I don't want to make a mistake. Everybody, percentage increase or decrease. It's final minus initial. Okay. Okay. Yeah. Yeah, yeah, yeah, yeah, yeah. Sorry everybody. Final minus initial over initial. Yeah, times 100. Thank you. Sorry, made a mistake there. I don't want everyone to make a mistake tomorrow. So, our final is 65 minus 20 over 20 times 100. We put that in the calculator. I don't have my calculator with me right now or my phone, but you would get an answer, right? You'd get a percentage and it would be a percentage increase. So, it should be a positive number. Okay. Right. Um, that would get you three marks because it would be like one, two for the 100 and then three for the final. That's what you would get three out of three for. Okay. Right.
Then it says for number three, scientists isolated a gene for glyphosate resistance from the weeds and used it to genetically modify the maize plants. There are something similar to this last year. Actually, I feel like this is the same question a couple years before. Um, it's literally the same question as it was last year. Explain the economic benefit of making maize that is resistant to glyphosate. So what is the economic benefit of making maize resistant? So remember when we talk about economic benefit, what are we always talking about? Money, everybody. We're talking about money. We are talking about less uh herbicides, right? We're talking about um more yield. In other words, more plants will grow. Um, so when we speak about economic benefit, we're always trying to save money by using less herbicide and growing more plants. So that's what they mean by economic benefit. It feels like a geography question to be honest, but they do like to ask this kind of thing. So let's be prepared for it.
And then I'm not going to draw the whole bar graph, but I will tell you what you would have got your marks for on Friday. A bar graph must have a heading, type, scale, label, plotting. 1, 2, 3, 4, 5, 6. Does the heading have both of the variables in it? The independent and dependent? T for type. Is it a bar? Um, hopefully we all drew a bar graph because I told you to draw a bar graph. S is for scale. Just as a top tip, when you scale, they are talking about these scale lines, but they're also talking about these scale lines. Hopefully, if you were, I'm just making up numbers, you went 10, 20, 30, and maybe over here it was like 2010, 2011. Do you know what I mean? You scaled it out properly. Um, L is for label. So this would have been time and year is the unit of measurement everybody. I think probably some of you didn't do that. Hey, you just went year. I don't know what they're going to do in the memo discussion. They might accept both. I don't know. And then P for plotting is did you plot your bars correctly? And that's what you get six out of six. So it's actually a really straightforward one for us. Okay.
All right. I'm going to have a look at the chat to just see if there's anything that I want to maybe wrap this lesson up with. We've got a little bit of time left and I just want to make sure. Um, somebody's worried here that it's going to be a pie chart. Just remember to be ready for a pie chart tomorrow, everybody. It could be a pie chart. So, bring a protractor and a compass and make sure that you're able to do that. If you don't know how to do one, I actually have done a question, a past paper question on it before. If you go into my playlist that's filled with past paper questions where I actually walk you through every single one. There is one with a pie chart. So you'll find the thumbnail and the thumbnail will have the pie chart behind me and that's the one you should go over with. Um, oh Tristan, you want me to do sorry, it's moving so quickly. You want me to do um how we modify antibiotics and stuff like that? Okay. Do you mean like natural selection? I think that's what you mean. We can quickly do that. Okay.
So, tomorrow they might ask you something about natural selection and um antibiotics or ARVs, right? So, it could be anti-antibiotics, ARV, or it can be um pesticides. I just want you to know they're all the same thing. This one is about bacteria resistance. Oh, oops. Resistance. This one is about virus resistance and this is about pest resistance. The idea is these are the organisms that are resistant. Okay? And so let me make a nice little little thing here. This is the organism we're affecting and this is the selective force. So now that you have an idea of those two, you put them together and you are able to explain natural selection. And natural selection in today's explanation. So you would go into your guideline and of course, we're going to learn natural selection off by heart, you know, where it's like there's a population with variation. Some are favorable, some are unfavorable. Now, if they're asking specifics like this one about antibiotics or ARVs, you can't just go some are favorable and some are not. Instead, if you were to, for example, do the antibiotic one, we need to know that antibiotics are the selective force and the organism we're resisting or affecting is bacteria, right? So you would go like there is variation in who the organism, bacteria, and then that's when you go, some are resistant, others not resistant, right? Resistant. Then you would go on to say, um, there we go. Sorry, it's not picking up my next point. Then you would go on to say, so some are resistant, others are not. Um, those that, uh, we would say natural selection occurs and then you would say, like the antibiotic kills the non-resistant, so they die. Whereas the resistant survive. Those that resist reproduce and then they go on to pass on their characteristics. And that's it, guys. Like I can do the same for ARVs. I could do the same for pesticides. The main thing is, as I've put there, is what is the selective force? Is it an antibiotic? Is it an ARV? Is it a pesticide? Is it a herbicide? Is it a medicine, basically? And then who is the organism that's resisting? Remember, it is the microorganism or the pest that is resisting. It is not the animal. So like one year we had pigs who got sick, right? A pig got sick with some bacteria. Let's say pigs got TB, which they can. I want you to know it's not the pig resisting. It's the bacteria living in the pig. That's what's resisting, everybody. And that is natural selection.
Remember, speciation is often confused with natural selection. Remember speciation, if I just quickly, I'm not going to write it all out because it's from your guideline, but remember speciation is when you have one population that splits into two, either with a river, a lake, an ocean, and over time they become so different, those two populations, that if they were to ever meet again, they would be unable to reproduce. That's basically what speciation is. Uh, I'll do this last one cuz I'm I must go everyone. I've been on for a while, but dihybrids, I see the questions. So, I want you to know that a dihybrid, you're never going to have to do the whole thing. Your focus for tomorrow should be, can you do the gametes and can you do the parents? So, what do I mean by that? Well, if the parents are this, right? Can you give me their gametes? So, remember it's like this letter and this letter go together. I do it like this. This letter and this letter, then this and this. So, that's A and big B. This and this. I just underline them so I keep track. So, there I've made the gametes. So, can you go from parents to the gametes and can the gamete, can you take the gametes and go backwards to the parents? That's the what I need you to be able to do tomorrow. So these two are important skills. They will never make you do a full Punnett square, everybody. They'll be like a question mark and they'll be like something like this. Something like that, guys, and you got to solve what is this? They're never going to make you do a whole one, okay? Ever.
Um, last but not least, actually linked to that before I go, let's just do a quick checklist. So, when you do your monohybrid tomorrow, which there will be a monohybrid, I don't know what they're going to ask you. They're going to ask you on like the color of feathers. Who knows? But, um, just just do a checklist. Must be P1 in the margin. And then parent times parent. Okay. And so I'm just going to literally put your color times color, like whatever that thing is. Then you need to put their letters, right? Uh, then you need to write meiosis in the middle. Then off to the side, gametes. And you put their gametes. I put my gametes in circles. If you don't, that's okay. But just make sure they're like far apart. I put mine in circles. I tell my metrics to put in circles because it's the safest thing to do in the metric exam. Then we write fertilization. I use a Punnett square, everybody. I hate line diagrams. They're really awful to mark and also you guys make a lot of mistakes. So I would never use a line diagram. But I would put my gametes in the right place. I'd fill out the whole Punnett square and then um I would then write the phenotype and the genotype. Now, what I write here is dependent on what the question wants. Do they want a percentage or do they want a ratio? Okay, so remember if it's 75% something and 25% something, what is that ratio everybody? It's 3 is to 1. If it is 50/50, then it's Whoops. Then it's one is to one. Okay. Um, nobody, no one, if you've watched any of my videos, should not be getting less than six marks for their their their monohybrid. No one should be getting less than that. Then you've made a mistake somewhere. Um, the one place you make a mistake is up here. You don't write out what the parents are properly. Please write them out properly. Please say male with green eyes. I'm just making it up. Or please write female with um, whatever the condition is. Let's go heart condition. Even if it's not sex-linked, which this one isn't, I would still put male and female in. I would still put the male and female, even if it's not sex-linked. It doesn't matter. Okay.
And I think that's it for it for today, guys. We've been on for quite a while now, almost an hour and a half. I think I'm going to let you go. You can go back as many times as you like to watch this video. Um, there are so many little nuggets of goodness that I have in my prediction video if you haven't gone to go watch it just yet. Um, and I would use the prediction video not just as like what I think is in the exam. I want you to use it as a checklist to see if you're actually ready and did you cover everything you should have. This particular video now will be live for you to go and watch again and watch portions of it. Go watch my playlist on uh past paper questions where I walk you through various ones from paper two. Um, as always, tomorrow natural selection, meiosis, and speciation will probably be the worst answered questions. So, those are the questions you need to prepare the most for. You need to be on top of your game when you explain yourself tomorrow. And I think you'll be fine, guys. I think you've done a lot of preparation. You're hearing this live now, which means already that you've taken an extra step to make sure you're ready. And I look forward to seeing the paper tomorrow. I don't think it's going to be easy. So, please just mentally prepare for that. Don't be caught off guard. And I will see you all again soon, everybody. Bye.