EASY TO UNDERSTAND | INTRO TO GENETICS

Hi everybody and welcome back to Miss Angler's biology class. I am Miss Angler and in today's video we are going to do an introduction to genetics. Now if you are new here don't forget to give this video a thumbs up, like and subscribe and turn your notifications on because I post new videos every Tuesday and Thursday for grade 8 to 12 biology. Also if you are new here don't forget to sign up for my membership on my YouTube page. You can find the join button on my homepage and you can have a look at the different perks that are offered being a member. Things like members exclusive videos, live lessons with me, question and answer sessions. So go check that out if you're looking for some extra help as you work your way through your matric year and into your finals. Now it's important to point out that this video is an introduction to genetics. If you're needing a little bit more detail you should go and look at my grade 12 playlist. There you'll find many videos covering monohybrid, dihybrid crosses, sex link disorders, a little bit more in depth. This video here is going to cover genetics and the basics around it. So let's just recap a couple of things. First things first, we know that in every cell there is a chromatin network and that chromatin network is found inside of the nucleus that we see here. Now when a cell is undergoing any form of meiotic or mitotic division, so meiosis or mitosis, that chromatin network is going to condense into chromosomes. Now if you're not so sure what a chromosome is or its structure you should go look back at my meiosis videos which I've linked above now so you can refresh your memory on all of those basics. Now a chromosome is a collection of your DNA and you'll have 46 chromosomes as a human and chromosomes are condensed pieces of DNA. So that means if I zoom in on just this chunk over here we will find this piece of DNA that has been condensed. Now DNA is the code of life. We know that it codes for all the proteins of the body. Everything from skin to hair and everything in between is made via this DNA. Now the sections of the DNA are called genes. In other words if I were to take all the information from here all the way down to there that would code for a specific characteristic. Now it's really important to get this terminology locked down. A gene is a type of a characteristic. For example your height, your hair colour, your eye colour, your blood group. Those are the characteristics that we find in genes and those genes express themselves physically so that we can see them in people. Now if you can see them that would be something like your hair colour but you can't see someone's blood group. You'd have to have a blood test for that but we still say that a gene is the way you express a characteristic. It's really important now to clarify this confusion between the word gene and allele because it's going to make it really difficult if we don't know the differences from this point onwards. So first things first as we've established already a gene is a characteristic. So I want you to think of things like your height, your eye colour, your blood group but those particular genes have variations or types and we call those things alleles and an allele is a variation of that gene. For example you have your eye colour gene and the variation of that gene would be a blue-eyed allele, a brown-eyed allele, a green-eyed allele. Those are all variations of eye colour. Eye colour is the characteristic and the actual physical colour itself is the allele or the variation. Now let's see these alleles in action. As we already know every human has homologous chromosomes or homologous pairs and you'll remember that from a previous video you have two chromosomes that are paired together and they are paired together because they carry alleles that are for the same gene. In other words they carry an eye colour or they carry your skin colour or something like that where they must be grouped together because they carry the same gene. Now we're going to get into more detail about how you actually inherit those things but let's just see what they look like physically. What does an allele actually look like on your chromosomes? So first things first, on these two chromosomes that you have, let's say hypothetically for example over here is where we find your gene for your eye colour. On your one chromosome that you have, you have a blue allele in that exact location and it must be on both sides because both sides of the chromosome are like mirror images of each other and then on your other chromosome you have a different allele. Let's say you had green eyes on this particular chromosome so that's your allele. Now you will notice that the gene is in exactly the same place on both of the chromosomes which means that it is the same characteristic, it's the same gene but the colours are different and because the colours are different we say that those are alleles. They are different kinds or different types and so what we have here is one gene but we have two different alleles is what we are seeing here, two different alleles. Now that we've clarified what an allele and a gene is, we now need to look at how do you actually pass those characteristics on and so in every human being you have 46 chromosomes and they come in pairs or homologous pairs. The pairs are made up of a maternal chromosome which you got from your mother and a paternal chromosome which you got from your father and what that basically means is for every single gene in your body you have two alleles for that gene. So as an example on here this particular person is going to have a eye colour gene on the one chromosome from mom and then on the other we are going to have maybe a different allele variation, maybe a blue variation for eye colour on the other. So what that means is for every single one of your genes you will have two alleles or two versions of that gene and you are going to pass those on to your children but separately and that comes down to having knowledge in meiosis and so these two chromosomes are not going to stay together. Based off of how meiosis works the maternal chromosome is going to go off into its own cell over here and the paternal chromosome is going to go off on to another different cell that will then continue on in the process of meiosis. This separation you may be familiar with when you think about anaphase one where we separate the homologous partners from each other. So now I've gone and I have placed those chromosomes into separate cells and they've taken their alleles with them and so that is why when you have children you can only pass one of your alleles on at a time. For example let's say that you were male and it doesn't matter if you're male and your maternal or your paternal is passed on it's not linked to your sex. In other words if you're male you don't just pass on paternal traits you can also pass on maternal ones. Essentially if you were making sperm cells maybe the sperm cells that were resultant of this particular cell are all going to have brown eyed alleles on them and then maybe all the sperm cells that come from this chromosome are going to have all the blue alleles on them and so essentially what I'm getting at here is when you pass on your characteristics you can only pass on one of the two alleles that you have at a time. You can never pass on more than that because if you do you have created a chromosomal mutation. Now to take this even further we need to describe these alleles in a way with letters and what we do is we use upper and lower case letters to describe the characteristic and in this instance because we are using eye colour brown and blue I'm going to use the letter B for now and I'm going to elaborate very soon as to why I'm using capital B's for the one and lowercase b's for the other. That has to do with whether or not the allele is what we call dominant or is it a recessive allele and I'm going to explain that next. Now that we understand how we inherit our alleles from our parents and that we always have two alleles for every characteristic we need to now see if these alleles come in pairs who gets expressed? Which one do we actually use because we don't use both of them all the time. In actual fact depending on the combination you receive it will determine what you physically look like or what characteristic you have and so that's where we play into a dominant and a recessive allele. Now when we speak about these alleles we often use letters and for now we're just going to use the letter B because it's you could use any letter. When we talk about dominant alleles, dominant alleles are ones that we use with a capital letter. When we speak about recessive alleles we use a lower case letter and that's how we tell the difference. Now how do you know what you are going to physically look like? That depends on the combination of your alleles. Now as an example below we have three possible combinations and they come in twos remember because you have to have two alleles of every possible gene. One maternal, one paternal. You will see that out of our first two individuals you could either have two capital B's or you could have a capital B and a lower B and then the third individual is two lowercase b's and you can see that their combination actually influences the way they look and we call this influence on the way they look their phenotype which is their physical appearance. It is how they look and that physical appearance so their color whether they're purple or white is influenced by something called their genotype or their allele and so their allele pairs are important. So let's have a look at the first allele pair in this first picture. There are two capital B's which means that this particular plant has two dominant in this case purple alleles as the key describes below. So that means 100% this plant is going to make purple only flowers no other options. The second version is where you have a capital B and a lowercase b. Now according to the laws that govern how genetics works which I do cover in a different video in the mono hybrid as well as in my types of dominance video which I've linked above now you will see that when you have this mixture you are going to only see the dominant allele or the capital letter allele because it dominates it masks the recessives it's going to come out purple. The third and final option is two lowercase letters and it's two recessive alleles that means that those two alleles are going to make a white individual and the only time you can ever have a recessive physical characteristic like in this instance being white you need to have two in order to have it. Now to summarize that when you are writing out these characteristics and specifically you are writing out the genotype you would say for example that this organism the first one would be homozygous dominant. Homo means the same dominant means that it has two of the expressed physical characteristics. If you have a mixture like a big letter and a small letter we call this heterozygous hetero meaning two different. Now if you have two smaller case letters you still use the word homozygous to describe the genotype. However we say homozygous recessive so that we can tell that oh this is referring to two small letters that are the same as opposed to two big letters for homozygous dominant. Now as always at the end of every video I like to do a quick terminology recap you can use all of these terms in your flashcards while you study it's the best way to study terminology. First things first we looked at the chromatin network which was a recap of a previous lesson where we looked at that long twisty noodle-like structure that has all your DNA it's only visible during interphase and it condenses into chromosomes. Chromosomes you have 46 of them they carry that particular DNA we spoke of earlier in the chromatin network and they are the ones that we will be dealing with mostly when we talk about alleles and being able to see them and pass them on and crossing over and stuff like that in meiosis. And then we looked at genes which were sections of the chromosome that coded for a specific trait that one might be your height your eye color your hair texture and we looked at variations of those genes which we call alleles remember that's a variation like you have the gene for your eye color that's the gene but then the variation would be green eyes or blue eyes and so that is the allele. Then we looked at paternal and maternal chromosomes which remember you inherit one chromosome from your dad one from your mom and likewise when you reproduce your paternal and maternal chromosomes they must separate from each other so that only one goes into each of your gametes. We then spoke about dominant characteristics or alleles which are the physically expressed alleles when there is just one present but if you want a recessive gene to be expressed you're going to need at least two and an example of this maybe in nature would be if you have brown eyes you only need one brown allele to have brown eyes but if you have blue eyes you need at least two small b's in order or two recessive alleles should I say for you to have blue eyes and lastly we looked at homozygous and heterozygous which refers to the combination of letters that you have you are either homozygous dominant which means you've got two capital letters let's just remind ourselves two capital letter b's or you are going to have two lower case that's what homozygous means dominant or recessive heterozygous means you have one capital letter and one lower case letter now that's all for today's video I hope you enjoyed it um if you like this video don't forget to give it a thumbs up and subscribe I post new content every Tuesday and Thursday and please turn your notifications on so you get the freshest content as soon as I post it and I will see you all again soon bye