hi this lecture is about patterns of inheritance this is how we inherit traits on our chromosomes those traits follow different patterns and you'll understand what that means a little bit better when we go through some examples the first person to really studied this topic and publish was an austrian monk named gregor mendel so it's sometimes also called mendelian genetics just a quick reminder that you have 23 pairs of chromosomes and this is a colorized picture of those 23 pairs of chromosomes remember that one of each came from the egg that made you and one of each came from the sperm that made you and when those came together they formed a zygote that first cell that divided many many many times to make all you every cell of your body came from that original zygote that 23rd pair of chromosomes are called the sex chromosomes and depending on if you're genetically male or genetically female those are going to be different but those first 22 chromosomes 1 through 22 are called the autosomes and when we refer to traits that are inherited on those first 22 chromosomes we call that autosomal in inheritance so when we use the term autosomal we were referring to those autism the first 22 chromosomes and males and females have those same 22. the 23rd pair called the sex chromosomes traits are going to be inherited a little differently there because if you're genetically female you have two x's and if you're genetically male you just have one x but you also have a y genetic females do not have that y so traits that are inherited on the y chromosome are not going to be present in a an individual who is xx also if you have only one x chromosome and you have a bad gene on that chromosome you don't have another copy of that gene to make that protein correctly and that's going to be a big deal when we talk about traits that are inherited on the x chromosome so when we're going through these patterns of inheritance a couple of really important things right off that are important to consider one is where is that trait inherited is it autosomal or is it on the sex chromosomes that's going to be important then what pattern it follows is going to be important as well there's going to be a lot of vocabulary associated with this lecture just to warn you right from the beginning and um you will probably want to take really good notes because these terms are very very important and we will use them again for other topics this semester let's start with just a quick reminder that you do have two of each chromosome so let's randomly say that this is chromosome number three and somehow i chose the crayon there so if it's looking fuzzy that's not your screen that is because i i accidentally chose that and let's now say that there is a trait that is on this chromosome number three and this is the one you got from dad in other words this is the one that you got from the sperm that made you and this chromosome number three is from mom in other words this is from the egg that made you that's how you got two of each chromosome if there's a specific trait on this chromosome number three from dad then your chromosome number three from mom has that same trait in that same location but since mom and dad are not identical twins the dna sequence for that trait is different from both of those parents so even though it's a trait that codes for the same protein in that same location the version that you got from mom and the version that you got from dad different dna sequence nevertheless we know that you can inherit the same version of that gene in other words the same allele from each parent or you can inherit two different versions let's just start from the very beginning with some pretend traits let's assume that these are rabbits and not humans and this is chromosome number three in rabbits and this rabbit on chromosome number three let's pretend that this is the fur color gene and let's assume that in these rabbits there is gray fur or there is white fur and those are the two possibilities graver and le and white fur those remember are called alleles different versions of the same gene this rabbit might have inherited gray from mom and gray from dad or maybe they inherited white from mom and white from dead or maybe they inherited one of each gray from one parent and white from the other those are the possibilities that these are the only two versions of this gene in other words if there are only two alleles for this trait then they either got two the same or one of each and there are some important terms associated with that so let's draw out those three possibilities this is going to possibility number one number two and number three and those are meant to all be the same size even though i do those little sausage-shaped chromosomes different sizes those are meant to be the same so this is the same chromosome chromosome number three and here's that fur color gene and it doesn't really matter in this situation if these are from mom or from dad so just remember this rabbit has two copies of that chromosome and let's say that this is one of the autosomes because it's chromosome number three and chromosome number three in rabbits is an autosome it's not a sex chromosome and there are two different alleles for fur color and let's say possibility number one this rabbit got gray from one parent and gray from the other parent so they only have gray alleles two the same in this situation this rabbit got white and white and now this rabbit got one of each gray and white there are terms associated with that so you know what two alleles that rabbit inherited if a rabbit or any individual has two of the same version of a gene they are called homozygous for that trait this term homo means same and zygus is referring to the zygote or that very first cell that formed when egg and sperm came together but in this case it's not referring to the whole zygote it's just saying for that gene you have two that are the same so that first individual would be homozygous this individual would also be homozygous meaning two alleles are the same in other words two of the same allele for that trait this third individual though they both those versions are different and this individual is called heterozygous for this trait hetero means different and that means this individual has two different alleles for that trait now we need a term to differentiate between having two gray versus two white and in order to understand that term we need to take this story a little bit further in all of these patterns of inheritance that we talk about these heterozygous individuals are going to be incredibly important because how that gene gets expressed in the heterozygous individual is going to tell you what pattern of inheritance you're looking at if you get two different versions of that gene how that gets expressed is going to be really significant in telling you what pattern of inheritance that trade follows in this pretend version of fur color if a rabbit has one gray for allele and one white in other words they're heterozygous for fur color and if that individual ends up being gray fur what that tells us is gray is considered to be dominant so gray fur in a heterozygous individual for fur color tells us that gray is dominant over white so when you have one of each gray is the one getting expressed that means white is what's called recessive so gray is dominant and white is recessive let's define what dominant and recessive mean in this example what they mean is a dominant allele is the one that is expressed in a heterozygous individual okay whereas the recessive allele is the one that is not expressed in a heterozygous individual so now that we've established that in this example gray is the dominant allele and white is the recessive allele now we can go back to our homozygous individuals and we can tell whether that individual is homozygous dominant meaning they have two of the dominant allele or homozygous recessive meaning they have two of the recessive alleles so let's go back here this individual gray and gray are the two versions of that gene they have so they're homozygous and we would now say that they are homozygous dominant meaning they have two of the dominant allele and this individual that has white and white they are going to be what's called homozygous recessive they have two of the recessive allele so that's how we differentiate between those two the only way we know which trait is dominant and which one is recessive is again looking at the heterozygous individual the trait that gets expressed in a heterozygous individual is the one that's dominant two more important terms right now that go along with this whole dominant recessive homozygous heterozygous and that is genotype is the two alleles an individual has for that trait and then the phenotype is really how that genotype gets expressed it's the physical expression of the genotype going back to the rabbit fur color is our example sorry that first rabbit was gray and gray that was the genotype and the phenotype is going to be how that genotype is expressed in other words what fur color does a rabbit have if they got a gray allele from one parent and a gray allele from another parent what fur color would they have gray fur they don't have any other option they got gray and gray so they're gray the rabbits that got white fur gene from each parent you can probably guess they got white from one parent white from the other that's their only option they have white fur that's their phenotype here's where it gets significant again the heterozygous individual if a rabbit gets gray from one parent and white from the other and these are autosomes so it doesn't matter whether the gray came from mom or dad or whether the white came from mom or dad we've already said that gray is dominant over white so the phenotype of these individuals is going to be gray fur in order to predict what offspring are going to look like based on the genotype appearance scientists came up with a method for doing what are called crosses between individuals looking at what the possible eggs are and the possible sperm when individuals mate and they do that using a square called a punnett square and i'm going to show you that in a minute but in order to do that we have to represent the genotype with a letter and that letter is going to be used in our cross and typically what happens is the dominant allele is represented with a capital letter and then the recessive is represented by a lower case of that same exact letter and i'm going to show you how that works so gray we've already determined is dominant we know that because in the heterozygous individual gray is the one that gets expressed so we're going to represent gray for allele with a capital g so the genotype of this first individual is big g big g in other words two gray alleles we're now going to represent white as a lowercase g why are we not using a w because if we use a w that doesn't tell us anything about which one's dominant and which one's recessive if we just had g and w it wouldn't tell us anything about which one gets expressed in the heterozygous individual so white is going to be lowercase g that means this third individual the heterozygous individual is big g little g and let's say that we have a rabbit that is heterozygous so we have a heterozygous mom rabbit and we have a dad that's homozygous recessive if dad is homozygous recessive that means dad is little g little g two of the same that's the homozygous part and recessive tells you that it's two of the white gene mom is heterozygous that means she's big g little g one of each this is called a cross we're crossing a heterozygous mom rabbit with a homozygous recessive dad rabbit and we're just looking at one trait so this is a cross that's just looking at one trait when you're just looking at one trait in the square it's actually called a mono hybrid cross it means you're just looking at one trait along the top it doesn't matter if you do eggs on the top or eggs on the side but we're going to do eggs possible eggs from mom here on the top and we're going to do possible sperm from dad on the side here remember that during meiosis wow meiosis is significant here in meiosis each of these rabbits are going to make gametes and during meiosis one this pair of chromosomes is going to get split up and this little g is going to go to 50 of the eggs and the big g's going to go up to 50 of the eggs so that means our possible eggs are 50 are going to get big g and 50 are going to get little g in dad he's homozygous recessive the only trait he has to give to sperm are a little g so 50 get this little g and 50 get the other little g during meiosis one says sperm little g little g now what happens in these squares are all of the fertilizations this egg comes together with this sperm and that gives us big g little g for this offspring then this big g crosses with this little g this little g crosses with this little g or they come together to make this individual and then the same here this one comes together with this one so it's all the possible fertilizations this shows you what all the possible outcomes are for offspring each one of these squares represents on average 25 percent of the offspring and the way this would get reported is we would say these two together equal 50 so we would say 50 of the offspring are big g little g and 50 are little g little g that represents the possible genotypes of our offspring we now need to look at the phenotypes of the offspring how does this get expressed remember that big g little g heterozygous those are going to be gray fur and little g little g homozygous recessive that's going to be white fur so on average 50 of the offspring are going to be gray and 50 are going to be white just so happens they end up looking just like the parents in this cross so this square that helped us figure that out is called a punnett square i need to write these really close together it's two n's and two t's obviously a person's last name probably the person who figured this out so a punnett square sorry i'm going to write that again looks like that punnett square is how we figure this out this cross in which one allele is completely dominant over the other allele is our first pattern of inheritance and it's called complete dominance in this story about fur color in rabbits gray was completely completely dominant sorry gray was completely dominant over white incomplete dominance one allele is completely dominant over another allele and what that means is in a heterozygous individual that heterozygous individual oops has the dominant phenotype in other words whatever that dominant trait is that's what the heterozygous individual looks like in other words in this example big g little g gives you gray fur which means gray is completely dominant over white to be more exact grafer is completely dominant over white fur this is the way that many many traits in humans are inherited is through this first pattern of inheritance called complete dominance and this is especially significant when we're talking about something more serious than fur color when we're actually talking about disease traits genetic disorders a lot of genetic disorders follow this pattern of complete dominance let's now take it a step further and talk about complete dominance with respect to genetic disorders the way that these are inherited through complete dominance i'm going to use cystic fibrosis as our example cystic fibrosis follows this pattern of complete dominance and in this pattern big c is normal and it's hard to i'm i'm doing this really exaggerated because this letter c is really hard to distinguish between the capital and the lower case little c is going to be cystic fibrosis let's talk for a minute about what this gene that's affected by cystic fibrosis codes for in your cell membrane you have proteins that allow salts to move in and out of the cell it's a transmembrane protein and in cystic fibrosis the dna code for that specific protein is incorrect and it codes for a misshapen protein and salts cannot move in and out of the cell salts accumulate and in response the body forms mucus especially around the lung cells this mucus damages the lungs the cells of the lungs and other cells in the body and over time ends up resulting in the death of this person it's a very very tragic disorder to inherit because there is no cure currently for cystic fibrosis we have done things to dramatically increase the lifespan of people with cystic fibrosis average lifespan used to be around 12 and now that average lifespan is even up in the 30s which is amazing but sadly these people most mostly all die if you have two copies of this gene which we all do and you have one bad gene let's say that this one is little c so long as you got one good copy of that gene you are making enough normal protein to not have full-blown symptoms of that disease this is going to be the bad copy of the gene so you're not making normal protein but so long as you have one normal copy of that gene you often don't have that disorder when that's the case then that means that trait is inherited through the pattern of complete dominance it's also important to note that that only is the case if it is autosomal so it has to be an autosomal disorder meaning it's inherited on chromosomes number one through 22 not on the 23rd pair of chromosomes and in this case the disease is recessive and normal is dominant so if normal is dominant and the genetic disorder is recessive then the what we call this disorder is we say that this is an autosomal recessive disorder autosomal tells you it's inherited on chromosomes 1-22 recessive tells you it's inherited on the recessive version of that allele that means normal is dominant over abnormal in other words so long as you have at least one normal copy of that gene you're going to make enough normal protein to not have full-blown disease this is the way that many many disorders in humans are inherited they are autosomal recessive disorders this is not always how diseases are inherited so this is only if something is called autosomal recessive that this is how it's inherited and in that case you have three possibilities to keep it a little straighter on these crosses i'm going to now for the crosses use a condition called albinism where a person is born without melanin in their skin so their skin is really really light in color and albinism is autosomal recessive so we would represent it with lowercase a for the genotype normal pigment in the skin is going to be a capital a this tells you that normal is dominant over the disorder so three possibilities a person could get two normal one of each oops or two of the disorder alleles this person would be homozygous dominant heterozygous homozygous recessive the only way you can have an autosomal recessive disorder is if you're homozygous recessive because if you get even one good copy of that gene you're going to make enough normal protein that you don't have the disorder let's do a cross a punnett square a monohybrid cross with albinism let's say that mom is normal pigment and she is homozygous dominant oops that means mom is big a big a and let's say that dad is heterozygous in other words he's big a little a let's do this cross we'll do mom's possible gametes on the top mom only has big a to give so fifty percent of the eggs are gonna get this big a and fifty percent are going to get this one so big a big a dad fifty percent of the sperm get big a and fifty percent get the little a so let's do our cross big a big a b a big a big a little a big a little a so this and this and then this and this so 50 of the offspring have normal skin pigment and 50 are heterozygous and also have normal skin pigment so for the g for the phenotype it's going to be 100 normal but for the genotype 50 are going to be homozygous dominant and 50 are going to be heterozygous if we're talking about a gene that causes a genetic disorder we call those heterozygous individuals something different and that is we call them carriers carriers are heterozygous they carry the disease traits and they have the ability to pass that on to their offspring but they don't have the disease or disorder because they are heterozygous this normal gene is completely dominant so they don't have the disease but they're called carriers because they carry that in their genotype and look what happens if twos two carriers meet so two carriers mate that means big a little a times big a little a and let's do the punnett square for that so on average by the way these these averages assume a lot of offspring so if this was an insect playing thousands of eggs this would be the ratios but if you're a human having babies every single time your offspring have a 50 chance of getting this gene in the egg and this gene and the sperm so these odds really aren't true odds if you're only having a few offspring this would be only if you're having thousands of offspring and that's how you can have in families multiple children having a genetic disorder when the parents were both carriers the odds of that are slim but it can happen and it does happen so looking at the percentages here 25 are big a big a which is normal 50 remember each square represents 25 so those two together are going to be 50 are going to be what we call carriers and it's important to differentiate between the carriers because the normal individuals don't even have the bad gene in their dna but the carriers do so even though they have normal skin pigment we call them carriers because it's a genetic disorder and they are heterozygous which means they could pass that on to their offspring and here we go these are the individuals that have the disorder so 25 on average little a little a and these individuals have albinism which is the genetic disorder that we were tracking with this cross and again every time mom makes eggs fifty percent get the bad gene and every time dad makes sperm 50 get the bad gene so it could be just by horrible role of the genetic dice that they have three offspring and all three of them end up having albinism or something worse you know there are genetic disorders that are deadly at a very early age things like tay sachs disease where the baby inherits a genetic mutation that causes a key enzyme to not be present or not be produced correctly it's misshapen and that baby has fats that accumulate around the brain and they go blind deaf they have multiple seizures per day and they end up dying by age three or four some horrible horrible genetic disorders that are inherited this way the only way the baby can have the disorder is if they have two bad versions of the gene and that's because these are autosomal recessive disorders meaning that normal is dominant so you if you are a carrier you don't have a full-blown disease you're making enough normal protein to not have symptoms of that disease so these again are only in genetic disorders that are autosomal recessive there are disorders that are what are called autosomal dominant and we will talk about those as well autosomal dominant disorders are a little more confusing in order to really understand autosomal dominant disorders i need to just remind you about autosomal recessive disorders again um i'm going to continue to use big a little a for a while just because it's easy to differentiate those two letters so remember that in autosomal recessive disorders that we just talked about big a big a is normal big a little a is what we call a carrier and little a little a means they have the disorder you have to have two of the recessive disorder sorry two of the recessive gene to have the disorder in the world of autosomal dominant disorders it's different it's a different outcome and that's because in autosomal dominant disorders a little a is normal and big a is the disorder in other words the disorder is dominant over normal and in that case this individual has the disorder and this individual has the disorder because this is the disease gene and this is normal and disease is dominant over normal so that one gets a little more confusing and i'm going to give you examples of this so normal is recessive in this pattern of inheritance so the only way an individual could be normal is to get two normal copies of the gene the way you can tell the difference is if an individual is heterozygous and they don't have the disease it's following this pattern if they're heterozygous and they do have the disease or disorder then it's following this pattern so that becomes a little more confusing in most cases this combination is so bad that this is lethal and that baby never develops so usually in these disorders that doesn't even exist by the time that person would be reproducing so that's a lethal disorder because it's too much of a bad thing remember this is the bad gene and you've got two copies of the bad gene that's really bad if it's bad enough that having one of each you have the disorder then having two is really bad classic examples of this one is huntington's disease huntington's disease is a very sad um degenerative disorder degenerates your central nervous system and people usually start showing symptoms of this very young like even in their 30s and by then unfortunately most people have you know had children because some people don't start showing symptoms until like their 40s or 50s but it's so much earlier than most degenerative brain and and central nervous system disorders so these people have signs of dementia pretty early on but they also lose coordination of their body huntington's disease is autosomal dominant autosomal dominant in other words it's an autosomal dominant disorder so in this case i'm going to use h since it's huntington's disease big h is huntington's disease we know that it's the big h because it's autosomal dominant that means the disease is carried on the dominant allele and we use the capital letter for that that means little h is normal three possibilities big h big h lethal too much of a bad thing heterozygous individuals have huntington's because there's enough bad here it's dominant that dominant the disease is dominant over normal the only way an individual could be normal is if they had two of the little h let's say that an individual with huntington's disease who doesn't know yet that they have it reproduces with someone who's normal meaning they don't carry the gene for huntington's disease and in fact they're not even called carriers because remember carrier means you have the disease gene but you don't have symptoms of the disease these people have full-blown huntington's disease if they are heterozygous so huntington's disease is going to be big h little h how do i know this because if they were big h big h they would not be reproducing that would have been lethal normal is little h little h so this cross draw our punnett square it's autosomal so it doesn't matter which parent has huntington's disease and which one is normal it doesn't matter if it's mom or dad so i'm just leaving that out of the story so sadly if you look at this on average 50 of the offspring are going to have huntington's disease and these 50 here are completely normal and they don't carry the disease allele in their dna so this would be 50 big h little h which is huntington's and fifty percent little h little h which is normal let's do another cross with an autosomal dominant disorder achondroplasia sometimes called dwarfism is an autosomal dominant disorder that means disorder is dominant and normal is recessive big d big d is lethal so that means people with dwarfism are big d little d and little d little d is normal so if i said that two parents have dwarfism you would know that they are both big d little d two heterozygous individuals is what our cross looks like so remember each square is 25 so 25 of the crosses are going to be lethal 50 percent are these two dwarfism but here's what's crazy 25 little d little d normal so these individuals both parents had dwarfism not only do they not have dwarfism but they can't even pass it on to their offspring because they don't even have that gene in their dna and that's because mom and dad were both heterozygous so if heterozygous individuals have the disorder you know that it's autosomal dominant there's no way for it to be autosomal recessive because in that case these heterozygous individuals would not have the disease or disorder so again quick reminder if it's autosomal recessive disorder we're looking at the heterozygous individuals to tell us big a little a is called a carrier no disease in autosomal dominant that's not the case in an autosomal dominant the disease is dominant over normal so in an autosomal dominant disorder big a little a has the disease or disorder so again looking at the heterozygous individual is going to be significant to know what pattern of inheritance you're looking at now we're going to look at something called incomplete dominance we've talked about complete dominance now we're looking at incomplete dominance so everything we've talked about so far is that pattern that's called complete dominance let's say that we're looking at a plant that is a flowering plant and big r big r gives red flowers and little r little r gives white flowers if this was complete dominance heterozygous individuals would most likely be red but what if i told you that big r little r gave pink flowers in this case the heterozygous individuals end up with what's called an intermediate phenotype something that's in between in other words both of those genes are having an influence on the flower color red is having an influence and white is having an influence it's almost like a blending of the two so you end up with an intermediate phenotype so heterozygous individuals have an intermediate phenotype a couple of examples of this in humans straight hair times curly hair gives you wavy hair the heterozygous individual has an intermediate phenotype ldl receptors on your cells ldl this is the bad cholesterol i'm going to use big l as my gene we're going to say big l big l lots of ldl receptors on your cells these are people who can eat french fries every day and not get high cholesterol we don't like these people just kidding we're just it's just not fair little l little l no ldl receptors these people get high cholesterol from an early age it's genetic they don't have enough ldl receptors to break down cholesterol if they have a poor diet if you're intermediate it's because you're heterozygous and this is an intermediate number of ldl receptors so if you eat healthy you're not going to have high cholesterol if you didn't healthy you'll probably have high cholesterol so again incomplete dominance heterozygous individual ends up with an intermediate phenotype somewhere between the dominant and the recessive not as common in humans incomplete dominance is that pattern so we've talked about complete dominance incomplete dominance this next one is a little more confusing it's called codominance and the best example of a trait that follows this pattern of codominance is blood type in humans we're going to do a blood typing lab it's the very last lab of the semester that we do in week 13. and in human blood type there are two major markers on your red blood cells that can be inherited one is the blood type marker and the other is what we call the rh marker so we're not talking about whether you're positive or negative so if if you have o positive blood or o negative blood we're not talking about the positive and the negative that rh factor is inherited by a pattern called complete dominance i'll talk about that a little more in a minute we're talking about are you type a b a b or o oops sorry i turned my ipad on accident so this is how it goes there are three possible alleles for human blood type and they look like this they're going to look a little bit different than everything we've looked at before this is the type a allele this is the type b allele and this little eye is the type o allele again i'm going to define codominance for you after i give the example because it will make marks more sense then so let's look at the possible genotypes the possible phenotypes for blood type in humans and when i tell you this story i'm also going to explain what that big guy and that little i mean a person can get two of the type a allele one from mom one from dad we would say that this individual is homozygous meaning they have two of the same allele they are homozygous type a but their outcome is that they have type a blood what that gene codes for is a specific marker on your red blood cells only on your red blood cells and if this is your red blood cell i'm going to draw a pretend marker shape your red blood cells would have this type a marker even just having one gene that says make the type a marker is going to give you the type a marker this person has two of them so they definitely have type a markers on their red blood cells again i'm going to tell you why that's a capital letter i in a second the other way that you can be type a is to get one type a allele and one type o allele because type a is completely dominant over type o so this individual would be heterozygous for type a blood and in this case this is saying make type a markers and this is saying make no markers because the type o allele says don't make any markers a b or otherwise on the red blood cells now again this doesn't have the rh marker is a separate marker this is just the blood type marker so if you've got one gene saying tape make type a markers on one say make no markers you're going to make some type a markers and you're going to have type a blood the same thing goes for b except that it's a different marker so you can be homozygous for type b blood so this person is type b blood the other way they could be type b is to have one gene that says make type b markers and one that says make no markers so type b markers are going to be a different shape so in this example let's give them a different shape so if you even have one gene saying make type b markers you're going to make type b markers and they have a different shape the only way that you would have no a b or o i mean i'm sorry a or b markers on your red blood cells is to get two of the type o this is the only way you can be type o and again that little i says this is type o no a or b markers what if you get an a gene and a b gene say you're this in other words one of those genes this one is saying make a type a marker and this one is saying make a type b marker you're making both because you have one of each kind of gene and in that case you're going to have type a b blood okay so what is codominance in codominance two alleles are not dominant over each other they both get expressed they can be dominant over a third but they're not dominant over each other they're what's called codominant so if you get one of each they're both going to be expressed and it makes sense if you think about what that gene is coding for o says don't make any markers so it's recessive right because if you have another gene saying make markers you're going to make markers these heterozygous individuals you can see that b is dominant over o and a is dominant over o but they're not dominant over each other so if you have an a and a b they are co-dominant so in codominance and sometimes codominance is hyphenated and sometimes it's not it depends on the textbook you look at either way is acceptable codominance two alleles are not dominant over each other both get expressed okay why the big i and little i big eye is referring to immunoglobulins and it's because if you have a marker that your immune system doesn't recognize as self it's recognized as foreign and you are going to produce antibodies against that blood type so if you have just type a markers and your type a blood if this is your genotype you recognize type b markers as foreign and you produce antibodies against type b markers and if you ever have got any blood with a type b marker on it put into your body those y shaped proteins the antibodies so this is an antibody it would bind to that red blood cell with the type b markers and it would cause your blood to clump and it's fatal very quickly same thing would happen in an individual that was type b if they got a type a marker put into them it's only what your body recognizes itself so type a b they can receive type a blood because they recognize that itself they can receive type b blood they recognize that itself everybody can get type o blood because it doesn't have any markers to make anyone's immune system angry so if you're typo you can't get a or b you you recognize both of those as being foreign and you're going to cause type a to clump and type b so if you're type o you can only get typo blood let's look at that chart for a minute of who can get what so let's go right here this is kind of a logic problem blood type can donate to which blood types and can receive from which blood types so let's go type a so if you're type a blood it means you have type a markers on your red blood cells who recognizes you as self others with type a and also type a b type a b has type a markers so they recognize itself who can type a receive from obviously type a if you're type a can you get type av blood no you cannot you would recognize that b marker is being foreign and clumped that blood but who else could you re see from if you're type a which blood type has no markers that would make your immune system mad it's the typo everyone can get typo similar story for type b blood you can donate to b and a b that you can only receive from type b and type o you couldn't receive from a b because the a marker would cause you to produce antibodies and clump that blood if you're a b guess what the b part makes a mad the a part makes b mad they both make omad so the only person you can donate to if you're type a b is to type a b that's it but you're lucky because you can receive all blood types because you recognize them all as being self you're called the universal recipient you can get anyone's blood your type o no marker no i'm sorry i call them markers but no a markers no b markers you can donate to all you are the universal donor but you can only receive from oh because any a or b markers are going to be perceived as foreign the story i've just told you does not include rh rh is the positive and negative part if you're rh positive it means you have the rh marker on your blood cells if you're rh negative it means you don't so if you're positive and positive then you're rh positive if you're positive and negative this gene says make the markers this says don't you're going to make the marker so you're going to be rh positive the only way you can be rh negative is if you got an rh negative gene from both parents this is a different marker it's called rh because it was discovered in rhesus monkeys this is the marker that if you have a baby with a different rh factor than you you could have problems because you produce antibodies against that and then the next baby you could have problems with um they give you a drug called rhogam to cause you to not um make antibodies against that baby in the future but that's a whole different topic but what i want to express to you is that this is a different pattern of inheritance it's complete dominance and in this story positive is dominant negative is recessive and the way we know that is because the heterozygous individual this individual is rh positive so that's how we know that positive is completely dominant so the positive negative is a separate thing so if you're a positive it means you have the type a marker and you have the rh marker okay if you're o negative it means no a or b markers and no rh markers so you're the true universal donor if you're o negative if you're o positive you can donate only to a positive b positive a b positive so the rh factor is a consideration when donating blood the true universal donor who can give blood to everyone is o negative type o is the most common human blood type so at some point in human evolution there must have been a survival advantage to not having an a or a b marker on your red blood cells and that's interesting because if we go back here remember that this is homozygous recessive usually recessive traits are less common in the population but in this case type o with no markers no a or b markers must have offered a survival advantage so maybe there was some type of parasite that attacked red blood cells and it only attacked those that had a or b markers hard to say um there are many parasites that attack red blood cells including malaria which is still a major killer on the globe but malaria doesn't discern okay malaria attacks all blood types equally but maybe at some point in human history there was something that didn't attack type o and in fact you know it's interesting because when coronavirus um coven 19 version of coronavirus first um started spreading there was you know a lot of hype about if you had typo blood you were less likely to get it that we know now that that's not true but there was some talk of that early on there's no there hasn't been a study that's confirmed that let's just say that at this point maybe some type in them at some point in the future they might decide that that there's a correlation there but right now there's no proven correlation between your blood type and how prone you are to getting coven 19 infection everything we've covered now those are all the autosomal patterns of inheritance so we had autosomal recessive and autosomal dominant disorders and those all covered oops complete dominance so complete dominance was the pattern and that included autosomal recessive disorders and autosomal dominant disorders and there was incomplete dominance where the heterozygous individual had an intermediate phenotype that's where red and white flowers made pink and then there was codominance where if you have both alleles they both get expressed so type a b blood if you have an a and a b those both get expressed if you have o that's recessive but a is not dominant over b and b is not dominant over a they're both dominant over o and that's because if you think about what they code for it makes sense those were all autosomal now we're going to talk about that 23rd pair of chromosomes and we're only going to talk about x inheritance not y so we're going to talk about what's called x linked inheritance if a disorder is carried on the x chromosome it's inherited differently in women than it is in men different in males versus females and again this is looking at are you genetically male are you genetically female and do you have the normal number of x and y chromosomes there are going to be five possible outcomes i'm going to use red green colorblindness as my first example of an x-linked trait and the way i'm going to show an x that has the colorblind gene is i'm going to do um a superscript c this is going to be colorblind it's not on the y so it's only on the x here are the possibles this would be a normal female meaning no colorblind gene both the x's are normal they don't have a bad gene for color blindness this is going to be a carrier female meaning that one of the x's has a bad gene and the other one doesn't the only way these females could have colorblindness is if both of their x chromosomes have the bad gene so this would be a colorblind female and i'm just going to draw a bad gene on that one bad gene on that one if you have one good working copy of the gene you're making enough normal protein to not have the disorder you're a carrier female so in this carrier example this normal x is making enough normal protein that this individual does not have the disease males are a different story males are xy females are xx so oops sorry wrong one this is going to be a normal male meaning no colorblind gene this male has colorblindness why he has a bad copy of the gene on his x chromosome and guess what he does not have another x so he doesn't have another opportunity to make a normal version of that protein he only has a bad gene he only has one x and so this is going to be color blind male there are no male carriers because carrier means you carry your you carrier you carry the bad gene but you don't have the disease there are no male carriers because even just one bad copy of that gene you don't have another x to balance that the way this person did that's why more males have x-linked disorders okay there are more males with colorblindness there are more males with hemophilia there are a lot of genes on the x chromosome and none of them have to do with gender okay the x chromosome we all have one you have to have an x to be alive you don't have to have a y to be alive but you have to have an x to be alive so that x chromosome codes for a lot of things that have nothing to do with gender if a male has a bad copy of a gene on that x he does not have another x to balance that and therefore he's going to have the disorder these crosses look a little bit different because now the gender of the parent and the gender of the offspring matter because the way that trait gets expressed in females is different than it is in males so let's do a couple of crosses let's have a normal female mate with a colorblind male and the way you draw this punnett square isn't as important as reporting the outcomes correctly and it's going to be different than the other punnett square in reporting the outcomes because now the gender of the offspring matters say normal female that means she's xx no colorblind gene the colorblind male we're going to show that as a colorblind x gene and a y that's just why it's not carried on the y chromosome so we'll do female here xx the male here there's his colorblind x and here's his y so 50 of his sperm are going to get the y and 50 are going to get the colorblind x during meiosis so now let's do the crosses x x c x y x x c x y so this is interesting because now you'll see that when we report our offspring everything up here these are all our female offspring and these are all our male offspring so now each square represents something different this is fifty percent of the females and this is fifty percent of the females so each of the squares now represent fifty percent of the females this is fifty percent of the males this is 50 of the males it just so happens that they're the same in this cross so we would say 100 of the female offspring our xxc which is carrier females so mom was not a carrier but they all got that bad x from dad so now they could pass that on to their offspring and this is interesting dad had colorblindness but all the males are normal no colorblind jeans let's do another one this time let's do hemophilia so hemophilia is an x-linked disorder this is the only time that gender matters for the offspring and the parents don't suddenly now make everything x-linked that's like i caution you for some reason once i introduce x-linked people want to do x and y for everything autosomal you don't do x and y's only one is x-linked let's say that mom is a carrier and dad has hemophilia so mom is a carrier i'm going to use the letter h now instead of the letter c so mom has that bad gene somewhere on her x chromosome but she's a carrier so that means she has a normal x also dad has hemophilia so he's this genotype again he has a bad gene somewhere on his ex so let's do this cross i'm gonna do dads up here so you can see how this can look a little different and we'll do mom's gametes over here now what's going to happen is our female offspring are going to be on one side and the males are going to be on the other so it's going to be divided this way now instead of up here it went this way it's just to show you that it doesn't matter if you put dad's gametes on the top or on the side that outcome is the same so it shows you that now our females those two cells look different and the same for the males this one's xhy and this one is xy so this with this and then this with that remember that each one of these cells represents 50 of the females so these are our females over here and these are males over here and on our females 50 of them are this which is colorblind females the other 50 of our females are this which is carrier females okay now our males 50 or this which is color i'm sorry it's not colorblind we're doing hemophilia these males have hemophilia remember there are no carrier males there is no other x to balance this so here these females this is a normal x she can make enough normal protein that she doesn't have hemophilia but this male he's got one bad ex he doesn't have another x to counter that so this is a hemophilia male and then guess what even though mom was a carrier and dead had hemophilia fifty percent of the male offspring are going to be normal no hemophilia gene so that is only with x-linked inheritance don't start doing x and y for every trade once you learn this one x-linked inheritance different from autosomal there are also traits inherited on the y-chromosome but we're only talking about traits that are inherited on the x so there are other patterns of inheritance we haven't talked about in this class there are times when it takes the combination of multiple genes to produce a trait such as your eye color your skin tone we're not going to talk about those patterns those are a little more complex you need to be able to do crosses with all of these patterns of inheritance there are practice problems online as part of the study guide so please do those practice problems they represent one problem for each pattern of inheritance also really pay attention to the questions that say you know you have this cross what would it look like in codominance what would it look like an incomplete what would it look like in complete dominance also don't forget this is really important i'm going to quickly scroll back up now because i want to show you something important really understand the difference between autosomal disorders and autism dominant disorders and again look at the heterozygous individual if it's a disease and the heterozygous individual has the disorder in other words big a little a sorry i keep pulling the highlighter here big a little a if they have the disorder then you know it's autosomal dominant if they're big a little a and they don't have the disorder then you know it's autosomal recessive so what that means is this big a is either normal or it's disease if big a is normal then you're looking at autosomal recessive in order to get that disease you would have to have two of the bad gene but in autosomal dominant this individual has the disease because in autosomal dominant disorders disease is dominant normal is recessive in autosomal recessive disorders disease is recessive normal is dominant and remember i drew a little chart for that way up here and remember there the possibilities are this so really make sure you understand that there are some some questions on the study guide about that and if you have questions about that please come see me and i can even give you more practice problems but the practice problems on the study guide if you can do those then you'll be good on the exam remember the exam is timed and you need to actually have some scratch paper to draw out punnett squares because the the answers are going to be multiple choice but you're going to have to do these crosses on paper and then i've got every possible outcome in the multiple choice answers so you actually have to do the cross on scratch paper and then choose the correct answer so you need to really be able to do a cross for each of these patterns of inheritance i know this is a long lecture sorry about that it's just a long topic and again i've only hit some of the patterns of inheritance there are more than that that we could have talked about okay thanks for your attention