Hey everyone, welcome back to my channel. So in this video, I'm going to teach you guys a really nice way to solve any pedigree question. Like it works every time guys.
This is an algorithm I created. So I really hope that you find it helpful. So usually USMLE questions on pedigrees will show you something like that. And wait a minute later. okay it will show you something like that and it will point to one of the offspring and then asks you what is the mode of inheritance of this condition all right so what i want you to do guys is to first look back at the parents so the first was the first question you need to ask yourself are the parents affected so the question will ask you about the offspring something like that highlighted here or highlighted here But I want you to look first at the parents.
If the parents are free, then this is a recessive condition. Just from the get-go. Now you know it's recessive.
If the parents are not free, when the parent is affected, then this is dominant. Alright? That's the first question you need to ask yourself so that you can get this over with, whether it's recessive. or dominant. And then after you've already figured out that okay parents are free and it's recessive now you need to know whether it's autosomal recessive or x-linked recessive.
At this point now you look at the offspring. Now if it doesn't matter the offspring affected may be male or female then it's autosomal recessive right it's an autosomal it's not on sex chromosomes. But if only males are affected, then it must be X-linked recessive. Okay, so follow this algorithm, guys. Now, what if the parents are affected?
Then it must be dominant. Now, my next step is to know whether it's X-linked dominant or autosomal dominant. The key to X-linked transmission in general is that no father can give his son an X.
So there is no male to male transmission. So if you find that the parents are affected and then it's dominant, if you find there is male to male transmission, as in a square transmits to a square, then this cannot be X-linked and it has to be autosomal. Right there in this example, for instance, a square gave a square so there is male to male transmission so then it must be autosomal we already know it's dominant because one parent is affected now if there is no male to male transmission you can see here that no square was able to give any other no squares the squares give circles only or circles just give their offspring but no square give another so no male to male transmission then it's x-linked if you guys follow this algorithm Even without looking at the question, I promise you, you will get it right every time.
Now, let's do some questions to reinforce that. Okay, so guys, this is the first I'm going to tell you, don't read the question. I can just look at this, I can just look at this pedigree and get it all right.
First, use my algorithm. Number one, are the parents affected or are they free? They're free. Then.
this is recessive. Now I need to figure out is it X-linked recessive or is it autosomal recessive. So I've already ruled out two answer choices here and now I'm narrowing it down to recessive options. Look at the offspring. Only males are affected then it's X-linked recessive.
That's it. I really don't need to go through this whole thing. It will cut your question time to short, very short. Now to the next pedigree.
Look at the parents. Are the parents affected? No, they're not. Then it's recessive condition.
Now I need to figure out is it X-linked recessive or is it autosomal recessive? Look at the offspring. Males and females alike, then it must be autosomal recessive. If it was males only, I would say X-linked, but this is the female. pointed here obviously says that males and females can be affected then it's autosomal recessive but the question here really asks it doesn't say choose autosomal recessive it goes one step further to the actual syndromes or the actual genetic disorders so you need to know that the genetic disorders with a structural defect are usually Those that are autosomal dominant and those with a functional defect or enzymatic defect are the ones that are autosomal recessive.
So I would choose in this case, I know the autosomal recessive condition here is classic galactosemia. Hemophilia B is X-linked. Huntington disease is autosomal dominant because it's a structural defect. And Leber hereditary optic neuropathy is mitochondrial. all right so guys i really hope this algorithm helped you it's something i created and i think it's helpful all the best guys