Genetic Inheritance, Autosomal Dominant, X-linked Recessive, Mitochondrial Disease Polygenic mtDNA

distinguished future physicians welcome to stomp on step 1 the only free video series that helps you study more efficiently by focusing on the highest yield material in this video we're going to be covering different types of genetic inheritance so things like autosomal dominant autosomal recessive x-linked recessive mitochondrial as well as a handful of other genetic concepts and terms this is the third video in my series of seven videos covering genetic specifically I'd like to point out the next video in the series which is going to cover pedigrees and the visual representation of ancestry of specific diseases that video is going to tie in really well with this one and there's sort of a combo so I suggest watching that right after this one and any particular gene locus you have a version for your mom and a version from your dad usually both versions are not expressed and only one of the genes affects the phenotype or the observable characteristics the gene that is expressed over another allele of the same type is called down individuals appear to have the phenotype of the dominant gene whether they have two copies of that dominant allele which would be homozygous or heterozygous have only one dominant allele so the person appears to have the phenotype of the down an allele whether they have one or two copies of that allele the allele that does not affect the phenotype when a dominant alleles president is called recessive recessive alleles only change the phenotype when there is no dominant allele present heterozygous individuals would have one dominant and one recessive and it like I already mentioned they would show the phenotype of the dominant gene however these heterozygous individuals that have one of the recessive genes are considered carriers for that recessive gene they themselves won't show the phenotype of the recessive gene but they can pass it on to their offspring an exception to this system would be Co dominance which we would most often see in the inheritance for different blood types in that case you can have two different genes both down at the same time that's why you can have type A and type B blood together when recovering dominant versus recessive alleles it's often shown in a Punnett square with the down mentally o being given the capital letter and the recessive allele being given the lowercase letter therefore a heterozygous who is a carrier for the recessive gene would be represented with a capital letter and a lowercase letter for each of the two alleles they have you can see here with the classic example of brown eyes versus blue eyes and brown eyes is dominant and blue eyes is recessive so here the capital B would be for brown eyes and the lowercase B would be for blue eyes and on the left hand we have both the alleles from the father and then on the top we have both the alleles from the mother and then in the four boxes in white here you can see the four different possibilities you would have by recombining the different alleles from the parents each of these four possibilities is equally likely to occur and you can see any of these combination sets highlighted in brown text is going to end up with brown eyes and any highlighted blue text is going to have blue office and you can see that 50% of the children on average are going to have brown eyes and they're going to be header as I get and they're going to be heterozygous for brown eyes and 50% of time they're going to be blue eyes with two of the recessive alleles together obviously if the couple has four children they might not get exactly two with blue eyes and tooth brown eyes but if they were to have a thousand children then you'd have about 50% as probability and chance to play less role if both parents for brown eye heterozygous individuals then you would only have a 25% chance of having a blue-eyed child and 75% of the time they would have brown eyed children with 25% of time being homozygous brown eye and 50% of the time being heterozygous brown eye even if the mother is homozygous blue all of the children will be brown-eyed if the father is homozygous Breanna and 100% of the children are going to be brown eyes with heterozygous for each gene and you can see here I give the autosomal dominant type of inheritance a high yield rating of four for those of you who don't know what that is it's a rating scale from zero to ten giving you a rough estimate for how important each topic is for step one and if you want to find out more details about the high yield rating you can go to my website here and check that out now that we reviewed recessive and dominant we can talk about autosomal dominant diseases these are diseases that are inherited in a dominant fashion and B gene that causes this disease is on won't be chromosomes other than x and y so the AutoZone would be all the other 44 chromosomes other than X or Y there's a long list of diseases with this type of inheritance but here are a few of the ones that are most commonly asked in these types of questions Huntington's familial hypercholesterolemia Marfan syndrome hereditary spherocytosis polycystic kidney disease and you can look up a whole bunch of other ones if you'd like online anywhere here's another way to graphically depict autosomal dominant inheritance other than the punnett square if you like that you can pause the video and take a peek at that autosomal recessive diseases are the same thing just the opposite we're talking about diseases that are inherited on chromosomes other than x and y that show recessive patterns of inheritance for whatever reason they'd like to ask more questions about the autosomal recessive than autosomal dominant cystic fibrosis seems to pop up a lot on these questions asking what type of inheritance that disease goes through most enzyme deficiencies are also going to be autosomal recessive lysosomal storage diseases PKU thalassemia and again there's a long list of other diseases that are autosomal recessive this is just a few of them here x-linked recessive diseases are the same thing as autosomal recessive diseases except that the gene that causes the disease is on the x-chromosome that complicates the situation a little bit because males who only have one X are going to get the diseases more often than females who have two x's because a recessive allele on the X chromosome in a male is going to produce the phenotype because there is no other dominant allele present so while autosomal recessive diseases you need to receive two copies that are mutated or damaged or have some sort of gene on it but for males they can get an x-linked recessive disease with only one affected allele for females x-linked recessive is pretty similar to autosomal recessive it just happens to be on the X chromosome because they still need to receive two affected alleles to get the disease there's also unique situations to consider such as males cannot pass an affected X allele onto a son because for a male to have a son that male has to give the son a Y chromosome so even if the dad has an x-linked recessive recessive disease there's no way for for that affected allele from the dad to get to a son he could only pass on that affected X allele to a daughter obviously males are going to be affected a lot more than females in the setup and women are primarily heterozygous carriers it's pretty unlikely for them to get the disease but it can happen as well they can get two affected x alleles one from each parent here's a small list of diseases with this type of inheritance muscular dystrophy hemophilia g6pd deficiency and a gamma globin immune now go back to the punnett square for the X and Y's it's the same thing but usually you show the X chromosome the Y chromosome with a superscript for what the gene locus is so consider here that we're talking about an x-linked recessive disease so the person highlighted in orange is going to have the disease and those highlighted in black are going to be fine so in this case the father is fine the mother is also fine but she's heterozygous so she's carrier for that recessive allele on the X chromosome 100% of the daughters of this couple are going to be normal half of those are going to be a carrier and the other half are going to have two normal alleles then when you're looking just at sons you're gonna have 50% normal sons and 50% affected sons we have the recessive genes now consider you have a carrier mother heterozygous carrier mother and a dad who is showing the disease so he has the Y chromosome and one affected X chromosome in this case 50% of the daughters are going to be affected they're going to be homozygous for the affected allele the other 50% are going to be carriers 50% of the sons are going to be normal and the other 50% are going to have the disease finally we can consider a situation where the mom has two normal genes and the dad has the disease in that case none of the children are going to end up with the disease you're going to have you're going to have 100% of the daughters be carriers but nobody's going to have the phenotype of the disease again here's a another way to represent x-linked recessive through picture if you like this you could pause the video and take a look you now can cover mitochondrial inheritance this is a little bit different because now we're talking about genetic material held in the mitochondria that's separate than the regular genetic material held in the chromosomes in the nucleus the mitochondria have their own separate DNA just for themselves and this DNA is only inherited through the mother the father's mitochondrial DNA has no effect on children heteroplasmy would be a situation where you have more than one type of mitochondrial DNA in your body and most of these situations are going to be when you've inherited one type of mitochondria and then it goes under some type of mutation during your lifespan the most common or at least highest yield disease with mitochondrial inheritance would be mitochondrial my apathy any red flag phrase for this disease should be ragged red fibers on a muscle biopsy curious mitochondrial inheritance via picture you can see that all the children of an affected mother become affected and none of the children of an affected father become affected so it's pretty simple if your mom's got it you're gonna get it if your dad's got it doesn't matter now I can go through a few extra genetic terms that are somewhat related to what we've been talking about so far polygenic is when the phenotype is not dictated by a single gene in this case more than one gene is going to determine the overall phenotype or there's going to be some interaction between genes and the environment this is going to be the case with most diseases and most overall types of inheritance specifically like they seem to like to ask questions about cleft lip and palate being polygenic it's also schizophrenia epilepsy baldness diabetes hypertension most diseases you think about are going to fall into this category variable expressivity is when the same genetic defect presents differently in different people you can have different severa T's different organ systems different signs and symptoms and a good example of this would be neurofibromatosis which I'm going to cover in a later video on the genetics section but some people that may have more contagious problems some people have tumors in different locations it doesn't present exactly the same with everybody mosaicism is when populations of cells within a single individual have different genotypes different genetic makeup this is due to post fertilization changes to those genes in most case it's going to be some sort of chromosomal abnormality caused by improper mitosis germline mosaicism is when only gametes or sperm and eggs are affected by the genetic defect therefore the individual themself won't show any signs of having the disease but they could pass it on to their offspring Leo trophy is when a single genetic defect can affect lots of different parts of the body multiple organ systems this is because that gene that's affected is expressed in multiple different organ systems so one genetic defect can affect multiple parts of the body incomplete penetrance is when not everybody with a genetic defect gets disease and again this is going to be common most of the time because incomplete penetrance really means anything other than 100% penetrance which is pretty rare neurofibromatosis is a good example of something with close to 100% penetrance and Huntington's disease also has a very high penetrance but most diseases are not going to have anywhere near 100% here are a list of here are lists of related topics which I give a high yield rating of zero and have decided not to include in my video to hopefully save you time and help you study more efficiently if you do choose to study these topics I would just suggest that you do so after you've already mastered all the higher yield material


  1. hello! great videos! extremely helpful and easy to understand. I take step 1 in the next couple of months. i am reviewing first aid and watching your videos as i follow along. im also doing u world questions. would you say this is suffice? also- do you have a video where you share your step 1 experience and how well you did? thank you so much!! 🙂

  2. Hey man! If you're trying to use a great mnemonic to remember the inheritance pattern of the actual diseases, I have a song on my channel that teaches you how to sing them out to the tune of a famous lullaby. I would appreciate it if you could check it out! Love your stuff. Keep it up

  3. Thanks for the information.  This has helped reinforce what we are learning in PA school.  I appreciate it.

  4. Well now Britains trying to stop genetic diseases from passing from mother child, with that new three person babies breakthrough, I think they're starting to play God alittle now.

  5. also recessive genes , can skip generations and a dominant gene can become recessive ,,in a short a time as 3 births from same male dominant. 

  6. man its well known mutations are occasionally passed through the mito from father to son. i think you need to update these vids.

  7. Thanks, this video was helpful , but one suggestion do it a bit more comprehensive .
    Please can you do a detail videos along with clinical scenarios on genetic mapping and diagnosis   

  8. If you liked this video and want me to make more please let me know by commenting, liking this video or by subscribing to my Youtube channel. If you have a question, please don’t hesitate to ask and I’ll try to answer it ASAP. 

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