hi everybody and welcome back to ms angler's biology class i am miss angler and in today's video we are going to be looking at the different types of dominance that we see in genetics now if you're new here don't forget to like this video subscribe and make sure you turn your notifications on because i post new videos every tuesday and thursday for grade 8 to 12 biology now don't forget if you're looking for some extra help when you are working on your exams coming up this year don't forget to go check out my membership once you join the membership you get access to exclusive members only videos we do live lessons together and you'll also be able to pick upcoming videos as well as summary notes on topics that you can use to study for your exams now there are three kinds of dominance that we are going to follow through here today they are complete co and incomplete dominance this picture really sums it up in a very basic way but i'm going to run you through the laws and the letters that you should be using when you complete your genetic crosses the first type of dominance we are going to look at is complete dominance and this particular type of dominance was originally coined by mandel and we're going to look at the law that governs this dominance as well as the basic definition so when we define our complete dominance we say that one allele is dominant over the other recessive allele now if you're not so certain about what dominant and recessive means you should go back and look at my introduction to genetics so you can familiarize yourself with that idea it goes on to say that such the effect that the recessive allele is masked by the dominant allele in a heterozygous condition now when they say masked they are saying you can't see the recessive allele if it is partnered with a dominant allele and we call that a heterozygous condition hetero meaning uh two different and in this instance they're talking about the alleles and the dominant and recessive combination again if you don't know what heterozygous means please go back and look at that intro to genetics video now let's look at this example because it makes it nice and easy to understand first of all i want to introduce the key that we're going to use for this example and when we are dealing with our complete dominance crosses we always use the same letter either in lowercase or in uppercase so big letters and small letters and in my key here a capital b represents black fur in mice and a small b represents brown fur in mice now what we have here is three outcomes depending on the combination of alleles that they have so first of all we have their phenotypes now remember phenotype means physical characteristic and genotypes refer to their alleles and what their alleles look like so if we look here we can see that the first mouse has two capital b's which means it's homozygous dominant it's got two dominant alleles and we know that capital lepers represent dominance and that means that this mouse is going to be black the second mouse however has a capital letter b and a lowercase letter b however it is still a black mouse and the reason for that goes back to the original explanation i said at the beginning where i spoke about the fact that if there is a heterozygous condition a begetter and a small letter you are going to get a masking of the recessive allele in other words when there is at least one dominant allele present the organism will express that dominant allele in its physical characteristics you'll be able to see it now the third option represents a mouse that is brown and it has two small or lower case letter b's and this represents what we call the homozygous recessive condition when we see this because in order to be able to observe any recessive traits whether it be hair color skin or fur it has to have at least two of the recessive alleles present in order to be visible now there is a law that governs this whole process and it came from mendel and we are going to need to know this for our exams it says that when two homozygous organisms with contrasting traits and what they mean by that is one is black and the other one is white or maybe one is blue and the other is green when we cross them all the individuals of the first generation in other words the first group of offspring that they will make we also call this the f1 generation will display a dominant trait so basically if we were to use our mice above if i took this black mouse up above here with a homozygous dominant allele and i crossed it with a brown homozygous recessive allele you would get all black now the reason for why you would get all black offspring from this particular cross is because of the law of dominance where if you just have one of those capital letters one of those dominant alleles all the offspring are going to express the dominant trait and you would need to be able to calculate this in a genetic cross using a punnett square if you're not so sure how to do these kinds of monohybrid crosses and using punnett squares you can click the video above the next type of dominance we're going to look at is incomplete dominance now you can already see the product of this dominance is very different when we cross two contrasting colors we produce a third different color now the definition for our incomplete dominance goes as follows it says that neither and that's important neither one of the two alleles of a gene is dominant over the other it results in an intermediate phenotype in other words the phenotype is in between when we are viewing it as a heterozygous condition in other words you have two different letters and so a beautiful example of this is with snapdragon flowers they do this very often and let's have a look at the key so we know what to work with now it's important that when you choose your letters in your crosses you provide a key if they provide you the letters then you use the letters they give you in the question but if they haven't given you any letters then you need to provide a key so let's just run through the key and why i've chosen these particular letters themselves so first of all like we did in the previous one we've used capital letters but you'll notice that we've used capital letters for both so where we see a capital letter r it's going to be red and when we see a capital w it is going to be white now you'll notice that i didn't use the same lettering like i didn't use just the letter b or just the letter w and that goes back to the incomplete dominance definition neither of these particular traits in the color are dominant over the other they're incomplete and so what happens is that when we bring them together they will make a new mix and so when we choose their lettering we get to choose the first letter of that particular trait so that means if we put a red and a white together or an r and a w together you are going to produce a pink flower and so we use this kind of lettering and i suggest that you do this because it's easy to keep track of combining these letters together and making a new color there are other ways that you can write this but this is a very simple way it's a way that you won't get confused because each of the different kinds of dominance have slightly different lettering that you're going to use as you can see now the last thing i want to talk about in terms of incomplete dominance is how do you actually get like a pure color and not a mix well that is where the whole incomplete aspect comes in order to make a red flower you have to have two red alleles for white same thing two white alleles but you'll notice there's no recessives or no dominance they are in this instance neither dominant and that's why they both get their own lettering but the moment you have one of each or what we call heterozygous you will end up producing a pink color or a mix of the two now don't worry in every exam they are going to give you a clue in a question about whether or not you are looking at a complete or an incomplete dominant question and generally the clue in their wording would be something like you have a red bird and a blue bird and when they reproduce they make a purple bird in other words it's like making a third different phenotype they won't always tell you it's a incomplete cross you are going to have to figure it out based off of the information they've given you the final type of dominance is what we call co-dominance and when we look at the definition for this it is similar to our incomplete dominance but i want you to note some important differences in codominance it says both alleles of a gene are equally dominant whereby both alleles are expressed in the phenotype in a heterozygous condition and so to break that down essentially it means that unlike incomplete dominance where there is mixing and making a new color codominance is taking two alleles that are equally dominant and when they are present together in the phenotype they share equal amount of the phenotype and this chicken example is a perfect example of what this looks like so let's look at the key that they have created for this now i quite like the way in which they've done this and they have used a capital letter c and then they have superscripted a capital letter b or w and this is quite a nice way to do it because you want to be able to tell the difference between all your genetic crosses so you want to be able to use essentially different versions of your letters for different kinds of crosses so that you don't get confused and this is a nice way to do that so it prevents you thinking if you write a b and a w for example just on their own you think maybe you're doing an incomplete dominant cross so it's quite nice to use this letter c because it's always going to make you think of co-dominant and so what we have here is codominant with a superscript capital b which means black then a c with a w for white and then if you put the two together with black and white at the top you get a speckled chicken or a chicken that is both black and white it's important to note here everyone that it's not a new color so we're not making a new intermediate color or a mixture instead i want you to think of a chicken that is black with white spots another example is like a cow that is white with black spots so it's not a gray car we're not mixing colors and making a new version of that color and so if we look at our phenotype options in our chickens here we've got black speckled and white speckled is just another way to say spotted and if we look at their genotypes that reflects their co-dominance so if we have two letter cs with the capital b's attached to them we will get a black chicken if we have two capital cs with the w's attached to them we'll have a white chicken if we have a c with a capital b and a c with a capital w we end up with a chicken that is black with white spots it could also be a white chicken with black spots so it's important to know that because codominant genes are equal it means that neither of the colors are going to dominate each other and so they share equal space in the phenotype now another very interesting type of dominance that we see and that you will need to know for your final exams is blood grouping dominance now what's interesting about blood groups is that some of the blood groups are both completely dominant but also co-dominant and i've actually made an entire video for this and it's going to be coming out next week so keep an eye out for that in your grade 12 playlist and i'm going to explain the genotypes that we see here and how they produce either a complete dominant or a codominant but just to give you a short rundown a and b are co-dominant to one another because you get an a b blood group so they can work together however o is recessive to everybody else so we see an example of what we call complete dominance but again i will produce a video separate to this one so to summarize and to start off with the original picture that we started off with let's just quickly look at the lettering that i suggest you use when you're working with complete dominant questions where one color is dominant over the other we are going to use a capital letter and a lowercase letter and generally we use the capital letter of the dominant trait so in this example a letter b for blue if we are working with codominance then i suggest we use the letter c capital letter c and we superscript it which means it's like the power of like two at the top and you'll see that i've used b for blue and y for yellow and when they come together you get an individual who is both blue and yellow equally when you are working with incomplete dominance i suggest you use the letters of both of the phenotypes so capital letter b is for blue capital letter y for yellow and if you have a b and a y together you make a green individual and these are the letters that would be universally accepted remember if they don't give you the letters you have to create a key there is only one particular grouping that you will need to always use the same which is the letter i which i go into detail in blood groups about why you use the letter i uh and oh i forgot also hemophilia um which i also touch on in my sex link disorders is the only other one that has a set letter which is the letter h now as always i'd like to finish off my lessons with a terminology recap please use these words to create flashcards and your study notes so in the beginning we looked at the law of dominance which it was a law created by mendel which basically explains that when you have two alleles one of them that is dominant one of them is recessive the dominant allele masks the recessive and you can only see the dominant characteristic we then looked at complete dominance which is again a product of the law of dominance where you see alleles that dominate other alleles so that's when you had like a capital letter dominating a lowercase letter then we looked at incomplete dominance incomplete dominance was where you took two alleles neither of them are dominant but when you mix them together you make a new intermediate phenotype like a mixture that's the one where we took a red flower and a white flower and we made a pink flower in codominance we looked at alleles that are equally dominant and we looked at the chicken example and another example be if i took a brown cow and a white cow and they produced a white cow with brown spots perhaps they show equal distribution in the phenotype we also spoke about genotypes which is the alleles those are the letters that you must use and the phenotype is the physical characteristics we also spoke about something being heterozygous which is when you have two different letters either you have a big letter and a small letter so a big letter b or a small letter b or you have maybe if you are a red and a white mixed together you make a pink flower that's a heterozygous and lastly homozygous means the same in other words two of the same letters so two big capital b's or maybe two capital w's and that's what homozygous means now as always if you've enjoyed this video please don't forget to give it a thumbs up subscribe to my channel and make sure your notifications on so you can receive the freshest content every week on tuesdays and thursdays and i will see you all again soon bye