Monohybrid Cross - Video Tutorials & Practice Problems

Monohybrid Cross

Hi in this video we're gonna be talking about a mono hybrid cross. So amano hybrid cross is just what it sounds like. So mono you get the idea of one and crossing means that you're going to the idea of mating something. So this is a mating that occurs between organisms to look at different alleles at one gene, that's where you get the mono hybrid from. So we're looking at one dream gene. We're looking at the offspring produced by this mating um from this one gene. And so when we look at mono hyper crosses, we do something called a punnett square, which I'm sure that you've heard of before. But remember that the gina types of organisms can be presented a different way. So you can have the dominant recessive with the upper case and the lower case letter. You can also have the wild type mutant and that's usually with a plus sign or the absence of a plus sign. Um So let's remember this when we go through our examples. So I have two examples here that we're gonna walk through on how to do this model hybrid cross using a punnett square. Um And so we're gonna start with this one first, the two hetero ziggy's purple plants. So now this is the mating to heterocyclic purple plants. That's who you're mating. So what does that tell you about the genotype and the phenotype of the mother and the father plant. So remember Jenna types of the alleles phenotype. So what you can see. So let's just start with the genotype is what in this question or the statement gives you information about the Jenna types. Right? So that's hetero Ziggo. So heterocyclic amines. What two different alleles? So if it's heterocyclic, guess we know that it has to have one dominant and one recessive. And so the genotype would look like A. And A. Because that's heterocyclic this and so I chose a just randomly. You can choose whatever letter you want. Um But that's what the genotype would be now if it asks about the phenotype. So I kind of already gave this to you. But what in here says what the phenotype is? Right, that's going to be use a different color. That's going to be the purple because that's what you can see. That's a color. And so the phenotype is for both the mother and the father are purple. I wish I had a purple pin but I don't. And so we're going to do this punnett square, which is what this thing is. I'm sure you know punnett square, then we need to know we need to have an allele in gametes. So here are the gametes, you have one gamut, two gametes, Three gametes. For gametes. Now remember the gametes, do they can take two alleles or one allele. Right? They contain one allele. And so you want to give one allele from the mother, you can do this one for the mother. This one for the father. If you want to flip them, you totally can completely up to you. Um But you need in each one of these squares where I have numbers. You need one alil. So if we're going to say that this is the mother then you take one uppercase letter which is the dominant and one lowercase letter which is the recessive. Remember where did I get this from? This is the genotype. And I took one allele and put them in each of the boxes. Now for the father you do the same thing. One allele in each of the boxes. Now once you have the these are the Gammy Alil. So these four are the gametes we write that 1-4 equals Grammys. Now when um these two organisms made those gametes will come together and fertilize. And so when they come together you now have to make those pairs to make the offspring. So the first thing you do is you take the letter from each corresponding row or column. So this A. Comes down here and this A. Comes here. So now you have an organism with two dominant alleles. So if we were to repeat this again, you would get this A. Comes here and you would get this A. Comes here. So now you have an organism with one recessive and one dominant allele. And you keep repeating this. You get this A down here and this A. Here and you do the same thing over here we have A. And A. Let me go over this. So this is A. And A. A. So the colors match. So now you have four offspring. So here are the four offspring and now they have all these different Jenna types. So when you get asked about the offspring, genotype is, what are you going to say is therefore Jenna types or how many Jenna types are there first of all? So you might say four because there's four boxes. But if you'll notice and look at them, one is actually the same genotype. So you have to dominance. You have a dominant and recessive and you have two recessive. Now you might ask why is this not considered a genotype? Well it is considered a genotype. It's written here because the order of the alleles actually doesn't matter. So I can write this this way or this one this way. But both of them are hetero guess and both of them are the same genotype, It's just written different. So there are only three Jenna types. This one this one and this one now when it comes to phenotype is how many phenotype sar there there 4321. Right. So there are two phenotype. And so this would be any of the ones with a capital A's in them would be dominant. And we know from the question that purple is dominant because both of the parents are purple and they're both heterocyclic. This that's how we know that dominant is purple. We have purple and then I didn't give it to you but it's just pretty much like not purple, you can choose whatever color you want. Purple is dominant and we'll just say white is recessive. So those are the two types. Now this one I just pulled out, it's pretty much just not purple because I didn't give it to you but it doesn't really matter. So that is how you do a punnett square for mono hybrid cross using dominant and recessive. But let's do this one now and this is with wild type and mutant. These are looking at flies and these are wild type wings and short wings. You have normal wings and short wings. And so this is um this is the mating. So we have a wild type wing fly with a mutant short wing fly. And it's asking for the genotype and the phenotype sis now the genotype we're gonna cross are going to be and I'm gonna tell you this because you can't necessarily tell this um from the question. So I'm just going to give it to you. So the wild type wing fly will say is homos I guess for wild type. Remember if you're talking about wild type, you use the plus and then the mutant short wing is going to be homos I guess for the mutant. This this is the short wing and this is the normal wing. Now the phenotype is I completely give you some water. The phenotype. So the mother has to wild type of eels. That means it's going to have the wild type wing and the father has to mutiny lille. So that's going to mean what kind of wing in the short wayne. So if we're going to do this again, let's see if you can walk through a little bit less help this time. So remember we have four gametes. 1234. So what alleles are going to be in each of these? Right? So you take the two from the mother and put them in each row for each column. And then you take the two from the father and you put them in each row. Now you start making the offspring pairings. So you take one from here and one from here. One from here, one from here, one from the top. Mm And again let me back out. So you can see that. So now we have four offspring with alleles from both the mother and the father. And so now it's going to ask for genotype and phenotype. So what are the genotype? How many Jenna types are here? Right, So you only have one genotype in the offspring? That's going to be the wild type? And the mutant allele because all of them are the same. And if you're looking at types, what's the phenotype, right? There's only one phenotype. And it's wild type because wild type here is dominant. You have to have two mutant alleles to show the short to show the short week. And we know that because of here we have the or the wild type wing fly and the mutant short wing fly. And in order to get the short wing, the father had two mutated alleles. So the only way to see that in the offspring is that the offspring had two mutated alleles. But it doesn't they have one wild type and one mutated. So you actually see the wild type phenotype. So that is how you do a model hybrid across. And just an introductory punnett Square. It's going to get a lot more complicated. I know you've probably done some of this in your intro class, but just reviewing these basics, make sure you really completely understand this before moving on. Because we're going to start getting into two traits and three traits and it gets much more complicated. Um So with that, let's now move on.

A black and white rabbit were mated. All F₁ offspring were black, and the F₂ offspring is made up of approximately ¾ black and ¼ white rabbits. 

• Draw out two Punnet squares detailing both matings.
• Supposed two white F₂ offspring were mated. What would be the phenotype and genotype of the F₃ offspring? 

• A. White, aa
• B. White, Aa
• C. Black, Aa
• D. Black AA

Which of the following offspring ratios is expected from a Mendelian heterozygous cross examining one gene?

• A. 2:2
• B. 3:1
• C. 9:3:3:1
• D. 4:2:1

Human albinism is a simple recessive trait. Determine the genotypes of the parents for each offspring combination 

i. A wild-type male and albino female have 6 wild-type children 

• A. AA x aa
• B. Aa x Aa
• C. aa x aa
• D. AA X AA
• E. AA x Aa

Human albinism is a simple recessive trait. Determine the genotypes of the parents for each offspring combination

ii. A wild-type male and albino female have 8 children, 4 wild-type, and four albino 

• A. AA x aa
• B. Aa x Aa
• C. Aa x aa
• D. AA X AA
• E. AA x Aa