hello anp2 class so I heard through the great point that some of you are having difficulty understanding concepts related to genetics and heredity so I thought I should put together a quick summary video explaining the differences between genotypes and phenotypes what do I mean by dominant versus recessive alleles the whole concept of dominant recessive inheritance patterns and also talk about sex-linked inheritance and of course how do you what's the importance of the punnett square and how do you use it to determine the probabilities of offspring having specific genotypes okay so let's get started I'm going to share my screen you right so here we go let's start with the basics this is only going to be a very quick summary so I'm only going to hit the the most important highlights of these concepts and give you some specific examples with the punnett square to show you how to fill out a punnett square how to determine probabilities and to kind of make sense and navigate the whole world of genetics okay but again this is a very very very basic video summarizing some of these key concepts okay all right so let's start with the vocabulary of genetics okay so most of the body cells have a diploid number of chromosomes and when you see the word deployed we are referring to 2n we're deployed number of chromosomes would have a total number of 46 chromosomes and so these 46 chromosomes are actually organized as pairs of chromosomes so you really have 23 pairs of homologous chromosomes okay for each chromosome all for each homologous chromosome au pair say chromosome 1 that pair consists obviously of two homologs one will derived from the maternal side so that was arrived from mom and the other homologue came from that the paternal side gets me you take the maternal and the paternal chromosomes or the homologs for say chromosome one you put it together and now you have the homologous pair for chromosome one and you would do this for 23 different pairs okay now off these 23 pairs 22 of these pairs are what we call autosomal chromosomes and the very last chromosomal pair the 23rd pair that's that's one pair of sex chromosomes which determines the genetic the sex of the person okay so if you were to kind of break this down for example let's look at a female and a male okay so a female have 22 autosomal pairs a male also has 22 autosomal pairs right the variation is here in the last set where this last pair of chromosomes which is the sex chromosomes would be different whether you are referring to a male what's a female in the female okay now let me orient you for just a second here the pink chromosome of the purple chromosome is from mom from the maternal side and the green chromosome is from dad from the paternal side okay so remember females only can give an X chromosome whereas a male can give an X or a white chromosome okay so again regardless of whether this is a daughter or a son in terms of offspring mom can only give an X chromosome does that make sense okay but the variation is from that what you would you get from the paternal side so my green chromosome here if dad gives an X chromosome then this individual this offspring ends up with an X X for its sex chromosome so therefore this person is a female xx okay now on the other hand if dad gives a Y chromosome then this individual has a genetic makeup of X Y and therefore this person is a male okay so males and females both will have 23 pairs of chromosomes 23 pairs means 23 times 2 and that's why you have a diploid number of chromosomes and every in every cell in the case of the female the female is gonna have 22 autosomal pairs about last set of sex chromosomes would be an xx genotype whereas the males would have the same 22 autosomal cares ok except the sex chromosomes for a male would be of the designation XY ok so that is in essence what we define as deployed okay now we've started discussing the male and the female reproductive systems as well in lecture and we started talking a little bit about sex cells gamuts like sperm cells and over now those cells don't have 46 chromosomes they're not deployed they are in fact haploid they only have half the number of chromosomes so a sperm or an OVA will only have n haploid number of chromosomes so therefore it has only 23 chromosomes total not 23 pairs of chromosomes okay all right so let's go on now that you've kind of understood the whole deployed concept and how many pairs of autosomal chromosomes versus the sex chromosomes let's move on to actually discuss what's going on on these chromosomes okay now chromosomes they contain DNA I've got to think back to a mp1 when we talked about nucleic acids there were two different varieties deoxyribonucleic acid DNA and why when you take acid RNA okay chromosomes contain DNA material DNA content and if you know the building blocks of DNA were what we called nucleotides nucleotides within DNA are four different types a c g and t okay so when you're thinking about any chromosome what I have depicted here is say chromosome one okay so remember chromosome one this is a homologous fair where one of the homologs was derived from the paternal side and the other homologue came from the maternal side and you put the two homologs together and now I have a homologous pair of chromosomes obviously for chromosome 1 in this case and you would imagine the same occurring for all of your 22 autosomal Affairs now I already talked to you about how it varies with the sex chromosomes xx for the females XY for the males ok so again I'm gonna focus here on autosomal chromosomal pairs so let's assume chromosome 1 here okay so this tonal and maternal homologue well they have millions maybe even billions of nucleotides on that chromosome organized as a C's GS and T's okay not all of that information is useful information okay I'm going to really simplify this okay and say that the useful information on these chromosomes is what we called a gene okay so I'm just the term I'm just gonna shown you here on this paternal and on the maternal chromosome at one particular location would be called lo sigh okay this particular gene X that's being represented at that particular location so what is a gene okay a gene is basically a sequence of nucleotides and since we're talking about DNA we're talking about a sequence of a CG and T that codes for some kind of useful information okay normally this would code for some kind of a particular sum some trait okay so obviously you have a gene X represented on the paternal homologue you also have a corresponding gene X on the maternal homologue alright so bear with me this is where we we're going to introduce this concept of alleles so what is a nelio matched genes at the same locus or location on homologous chromosomes is what we call an allele so here's the allele for gene X on the paternal homologue and at the same location to match what you saw with the paternal homologue you have another allele for gene acts on the maternal homologs so both of these at that particular location is what I called an allele that's coding for gene X and it codes for some useful information like the expression of some kind of a physical trait and again if you think back to a mp1 a lot of these genes also coded for proteins different proteins are synthesized in your body since we are talking about genetics here I'm gonna I'm gonna focus on how these genes actually code for physical expression of a trait and this is where we're gonna kind of lead towards this differentiation between what is a genotype versus of phenotype okay so alright so when you're looking at these two alleles for this particular gene X on this particular chromosome say one okay you could think about these alleles in two different ways okay so this is what this is where I'm leading towards this concept of inheriting or a pattern of inheritance when when you're referring to it as dominant and recessive inheritance okay so these two alleles so this one let's let's start with the paternal allele okay this allele could be a dominant allele or it could be a recessive allele normally a dominant allele is written as an uppercase letter so let's say an uppercase B or a recessive allele is written as a lowercase letter like this lowercase B okay so depending on the combination of these alleles on the paternal and the maternal either you have two dominant alleles or you have two recessive alleles or you have one dominant one recessive allele that in essence is what we called a genotype okay and that means genotype is a genetic makeup or the genetic combination of these alleles okay and what what does that mean the gene the genotype or the combination of whether this is dominant or recessive or a combination of that would code for some kind of particular trait some kind of a physical expression off a trait okay so bear with me I'm gonna explain this on the next slide and we're also going to talk about what is homozygous and what is heterozygous expression of alleles okay so very quickly genotype is a genetic makeup or the genetic combination of these alleles and the genotype depending on what genotype the individual carries that's going to code or determine the physical expression of the phenotype in that individual okay so I put together my own notes here and again for the sake of time I'm going to present I have the entire thing kind of put together on one slide but I'm gonna break this down for you piece by piece okay so let's assume okay I kind of going back to what me but we've been discussing on the previous slide let's assume a homologous pair of chromosomes and let's just say I have here in green this is the paternal homologue from dad and the purple chromosome is the maternal homologue from mom so this this is one homologous pair of chromosomes right this could be chromosome one it could be comes on - it becomes on three and so on and so forth okay let's just say this is chromosome 13 for right now tell you why in just a little bit okay so going back to what we just talked about a while ago you have a combination of nucleotides or genetic sequence of a C's GS and T's that are expressed on this particular homologue for the mom and the end the dad and of course that's the chromosomal information right so we just talked about okay what if at a particular location right you had a gene and the 8th row but matched genes at the same location on both the mom and the dad the maternal and paternal homologs so both of these at this particular location would be an allele for that gene X okay so remember an allele is a matched gene on c on the same location offer homologous pair of chromosomes okay now I just told you a while ago these are Leo's could be either a dominant or a recessive allele always the dominant allele is represented as an uppercase letter so in this case the uppercase P recessive allele is lowercase so therefore the lowercase B okay now let's think about the possibilities here okay now remember it we're talking about this particular gene X okay what are the possible combinations of alleles that you can put together for both the paternal and the maternal side okay so maybe and I have here again everything in green is I'm showing you the alleles on the paternal homologue everything in purple is shown you the allele for the maternal okay so maybe the allele for gene X on dad here on the paternal side is a dominant allele remember dominant is an uppercase letter right and maybe okay mom is also bringing a dominant allele so that uppercase purple B okay so that's the first scenario so both the both alleles on paternal and maternal both of them are dominant okay or here's the second scenario maybe on that side it is the dominant allele but on mom's side it is the recessive allele or the third scenario where you swap maybe dad's bringing a recessive allele and mom's bringing the dominant allele right and here's my fourth scenario where more both maternal and paternal alleles for that particular gene are both recessive alleles so those are your four possible combinations if you were to mix and match the ways in which you can put together an uppercase B and a lowercase B okay in other words how would you put together a dominant and a recessive allele okay so those are your four different combinations of how those alleles could be paired okay so remember this is where we're gonna bring in the concept of homozygous was heterozygous homozygous means hormone equals same hetero equals different okay so let's look at that for scenario right there you've got two dominant alleles so it's the same dominant allele therefore this expression if you put together those two dominant alleles this is what we call homozygous and yes its dominant because it's the two uppercase B okay now let's look at the second scenario you have a dominant allele and it's paired with a Salil right so these are different alleles they're not predominant they not both recessive there's one dormant and one recessive therefore this condition is heterozygous but always remember a dominant allele masks or silences are recessive allele okay so here I see a dominant allele and a recessive allele but that dormant allele as the word suggests is dominant it dominates over the recessive allele so therefore this scenario this scenario number two is heterozygous dominant oftentimes um when we discuss genetics like this we we may just say heterozygous it's understood when you differ when you're referring to dominant recessive inheritance patterns when you say heterozygous you you automatically should know that it's the dominant allele that dominates or what the recessive allele or mass the recessive allele so that's why I put this in in parenthesis because you could either call this heterozygous dominant or just heterozygous because it's understood okay now in the third scenario we just swapped the alleles between mom and dad but it's still heterozygous right because you have a lowercase recessive and an uppercase dominant therefore it's still heterozygous okay and then in this last scenario here you have two lowercase B so therefore this is homozygous because it's the same recessive allele on both mom and dad and because it's a recessive allele it's homozygous recessive okay so this is how you would distinguish between homozygous and heterozygous and hopefully you understand Anna what I mean by dominant versus recessive okay so those are the four different combinations of pairing of alleles that could code for some kind of a trait now that's what I'm leading towards next game now this gene X with its two alleles the uppercase B and the lowercase B right it calls for some kind of a physical trait it could be any number of different traits in your body I'm gonna use the example of say eye color okay so remember we're talking about a dominant allele uppercase B ah normally when we think about eye color this would be the dominant khalil allele would have more pigmentation so therefore this would be say brown eyes okay and the recessive allele which is the lowercase B would have less of the pigmentation so this would express a physical expression would be blue eyes okay so this idea of you having brown eyes or blue eyes that's the physical appearance of how your eyes would look right so therefore this blue and brown eyes this is the physical expression of this straight okay which is what we call a phenotype so why do I use the example of chromosome 13 there's a since I use an example of eye color there's actually about 16 or 17 different genes that code for the appearance of eye color there's two genes that are the most most well studied if you will and they are oca2 and herc2 which you don't really need to know but I'm just giving you an example of chromosome 13 here because I'm expect and kind of explaining eye color okay and I kind of simplified this down to just one gene but really sometimes this is much more complicated then I kind of understanding it as just one gene it may not be just one gene that determines the physical expression of a trade it could be as in the case of eye color like I just said it's more like 16 different genes okay but we're going to keep it simple right we're just focusing on one gene okay so when we go back to this concept here that we've been talking about dominant versus recessive alleles right if you take these combinations of alleles that were expressed on the paternal and the maternal homologs okay and you put together those four different possibilities and that's kind of what I've written down here remember we said the dominant allele is always represented as an uppercase B so that's going to code for or that's going to yeah that's kind of code for brown eyes whereas the recessive allele in the lowercase b codes for blue eyes so if you're looking at this okay say you had the dominant from mom and dominant allele from dad you have this particular combination now remember all of these this is the action combination of alleles on the maternal and the paternal homologs these actual combinations of alleles are what we call genotypes and the genotype will determine the physical expression of the trait namely a phenotype okay so if you're looking at this genotype and you're looking at two dominant alleles there now remember darman allele is going to always override or silence a recessive allele this is not a problem here because you're talking about two dominant alleles okay so remember the dominant little codes for brown eyes so therefore this individual if you have this makeup this genetic makeup of uppercase B uppercase B okay this will code for brown eyes okay in the second scenario you had a dominant allele and a recessive allele but remember the recessive allele is suppressed in the presence of one dominant allele so if you had at least one dominant allele then the expression the physical expression associated with the dominant allele is what you're gonna actually end up with so in this case you have one done in one processor you're going to still end up with brown eyes you won't see the expression of that recessive allele because it is masked by that uppercase P okay and the same here on the in the third scenario is just swapped so you'd still have brown eyes the only scenario where you see this condition here where you see the two recessive alleles only then would you actually end up with the recessive phenotype namely blue eyes so in the case of dominant recessive inheritance patterns okay if you have two down and alleles or if you had one dominant if you had at least one dominant allele then the phenotype associated with those genotypes would be whatever is associated with the dominant allele in this case brown eyes came the only son you would end up with the recessive phenotype is if you had recessive alleles on both the maternal and the paternal homologs of that home zone okay so hopefully you understand that now what is the difference between genotype and phenotype so everything that you see in this box here those are all genotypes the genotypes carry the allelic information the genetic information like those four varieties right there okay now the the lilyc combination will determine what the phenotype or the physical expression of that trait needs to be so the physical expression of the trade in this particular example was either the appearance of brown eyes or blue eyes okay okay so now that we've talked about what is dominant recessive inheritance I'm going to use some of this information to explain to you okay what is a punnett square okay so I'm going to use the same example right with the brown eyes blue eyes and everybody should understand by now the domina leo uppercase B would code for brown eyes and the lowercase letter B which is a recessive allele it will code for blue eyes okay so a punnett square is basically something that biologists use to predict or to determine the probability of the offspring having a particular genotype and so for this you would need to know if you would need to know the genetic information that's coming from the maternal side from mom and the information coming from the paternal side namely that okay so in this case okay so let's look at one final square it's kind of drawn like this okay where you put mom's information on one side and dad's information on the other side so female is designated by this symbol right here which is kind of written across the top there and the mail which is dads information is designated by that symbol and it is written down this column okay so for just to kind of be able to understand what's coming from mom was coming from dad again this is kind of color coded mom written in purple and dad's information is in green okay so let's say mom in terms of eye color because that's the example we're talking about red let's say mom has this particular genotype an uppercase B and a lowercase B in other words mom has one dominant allele and one recessive allele right so this particular genotype should tell me that mom has brown eyes because remember the phenotype associated with the upper case B is brown eyes lower case B is blue eyes but always dominant allele silences or masks the expression of that recessive allele so therefore since I had one dominant allele I'm going to mom's gonna have some eyes okay and let's say dad has the same genotype right there so hopefully you you kind of understand right the genotype will be this combination of alleles that's the genotype which yields the expression of brown eyes brown eyes being the phenotype okay so let's assume that dad has the same genotype so that also has brown eyes okay now if you were to mate mom and dad right and you had what type of eyes or what kind of combinations of eye color would be offspring end up with okay and that's what upon it Square kind of determines alright so you're going to write mom's alleles I'm gonna separate them out across the top there and dad's alleles would be across the bottom I mean across that column there okay and the reason for this is if you remember mom generates the a sex cell called OVA and that generates this excel force phone right now the OVA and the sperm are haploid they are not deployed they are haploid they only have half the genetic information so in other words and over or from mom could either contain the dominant allele or it could contain the recessive allele but it cannot have both right because that's the whole concept of meiosis and how you reduction in the genetic content by rising in all of the sex cells regardless of this famous sperm cell or an OVA okay and the same for dad so when dad dad sperm right fertilizes mom's over a sperm cell could either contain the dominant allele here okay all the recessive allele but not both okay so that's why you can't splitting it up like that okay so now when you think about the probabilities of combinations that the offspring could end up with the way you would kind of fill out a punnett square is simply this I mean this is this will come with practice but it's pretty straightforward so I have again in purple that's mom's alleles and in green you've got dad's alleles so I would just fill in down the column in the case of moms alleles and I'm gonna fill in across the role for dads alleles okay so you can kind of see the arrows and it's all color-coded so I'm gonna just bring this down in a lil upper case B down you wanna bring the recessive allele down right there then I'm gonna do the same for dad but I'm gonna walk across the row in this case so I'm gonna take this dominant allele from dad and write it across and then I'm gonna take this recessive allele from dad and write it across okay so now you end up with okay four different possibilities right when when this combination this genetic combination of mom and dad yield offspring there's four different possibilities okay and of course this is all these are all genotypes that are coding for what some kind of a trait this trait that we're discussing here is eye color okay so let's look at this okay so you end up with four different offspring so this offspring right here they have this person has this person could have two dominant alleles and then the second possibility here is one dominant one recessive likewise with the third possibility and then I end up with the fourth possibility here where it looks like I end up with two recessive alleles okay so now I'm asking okay if you if you generate offspring from this particular combination of mom and dad okay and this is their genetic makeup coding for whatever physical expression what's the possibility or the probability that the offspring have and these are the questions that you would ask okay I'm giving you four different examples here on the right so let's look at this first let's talk about homozygous and heterozygous okay so when you're looking at this first possibility here these are two dominant alleles so therefore this would be homozygous dominant in the second possibility here this is one dominant and one recessive allele so this is heterozygous dominant sure okay and then the third scenario here two one hum are one recessive one diamond allele so therefore this is heterozygous and here in this last case you have the two recessive allele so this is harmless I guess recessive okay and if you're looking at these different genotypes how would we determine the physical expression of the trade how would you determine the phenotype would this person have brown eyes or blue eyes right so since you have two Dorman alleles this wasn't going to end up with brown eyes and here you have one dominant one recessive always dominant is going to silence the recessive allele so therefore this person still going to end up with brown eyes those brown eyes matches that dominant allele okay same here one dominant one processor so you're gonna end up with brown eyes only in this last scenario since you have the two recessive alleles and remember recessive codes for blue eyes so therefore there is no DOM and allele to silence that recessive allele so you have a double recessive combination and that's why this individual would end up with blue whites right so now you kind of understand one two three four the four different genotype possibilities which results in obviously it's corresponding phenotypes phenotypes meaning brown eyes versus blue eyes okay so let's look at these four examples here on the right so you could ask so many different questions using this punnett square example okay so I could ask it what's the probability that the offspring have brown if you're looking at this there's four possible offspring right how many of them would have brown eyes well you got one two three three out of four okay so three by four is a 75% probability that the offspring had brown eyes so I could also ask it was a probability that the offspring have blue eyes well that's one out of these four possibilities so one out of four is 25% okay I could also ask you okay something like this what's the probability that the offspring are heterozygous remember heterozygous means I've got one dominant allele and one recessive allele right so I'm looking for this combination an uppercase P and a lowercase B well that is not it that's a that's a homozygous dominant or heterozygous condition and here's another heterozygous individual so it looks like two out of the four possibilities two out of four which is a 50% probability that the offspring could be heterozygous or I could ask it was a probability that the offspring are homozygous recessive homozygous recessive is very clear homozygous means the same allele and I'm talking about two recessive alleles because I'm discussing how much is recessive here so I'm looking for a lowercase B lowercase B that's only once and I will write here one out of the four possibilities so that's my probability of 25% so that in essence is how you would fill out upon a square given the Jinna the genetic information of the genotypes of mom and dad for a particular trait for a particular physical expression of a trade now you can imagine if you changed moms feel a genotype or you change dads genotype or you change both the genotypes depending on what the genotypes are you would separate out the alleles and you would fill out this punnett square and you would get different probabilities of the offspring having brown eyes or blue eyes or heterozygous dominant dominant or homozygous recessive and so on and so forth so this is a very useful tool that biologists use to determine the netic probability right that you that the offspring from a given maternal and a putana genotype what the offspring would end up with in terms of genotypes so that's a quick explanation of a punnett square using the concept of dominant recessive inheritance patterns okay okay which then brings me to this next concept which is sex-linked inheritance so y'all remember we said body cells are diploid 2n which means they each cell has 46 chromosomes organized as 23 pairs of homologous chromosomes after 23 pairs 22 pairs were autosomal pairs and that's where we talked about dominant recessive inheritance patterns and expression of hair color and eye color and so on and so forth okay you have freckles and do you can hear are you able to roll your tongue rollers things like that okay what I'm gonna talk about next is sex-linked inheritance so I'm talking about the expression or the inheritance of specific traits that are coded for by alleles on the sex chromosomes okay so remember the the last pair of all of your chromosomal pairs determines the sex of the individual so if you had if you ended up with an X X that would make you female if you had an X Y that would make you a male so I'm talking about genes that are coding for specific traits on the X chromosome and on the on the Y chromosome and here I'm mostly focusing on x-linked sex-linked inheritance pattern so which means I'm talking about genes that are found only on the X chromosome okay remember we talked about him a failure earlier on in the semester where this was a clotting disorder due to insufficient cutting factors so this life-threatening condition is caused by a recessive allele that is presented on x-chromosome okay so since this is a sex-linked trait we have got to talk about the genetic makeup of the males and the females and kind of keep that in mind but also combine the the concepts of recessive and dominant inheritance okay so in the case of females a genetic makeup of that sex chromosome should be xx whereas males have a genetic makeup XY remember the X chromosome and in both males and females that came from mom where is dad can contribute either an X or a white chromosome okay so in the case of females you have one X chromosome from mom and the other X chromosome from dad in the case of males this X chromosome came from mom and the Y chromosome came from dad okay so what we need to keep in mind now is how do you tie in the inheritance pattern for this recessive condition of hemophilia and how do you integrate it with the genetic makeup of xx and XY now again to recap a dominant allele as always designated as an uppercase letter in this case we're going with the uppercase H and so therefore if you if a person had expression of that dominant allele you would be normal okay whereas the recessive counterpart is the lowercase letter H and if you had two of these recessive alleles then that person would end up having hemophilia okay so when you are designating sex-linked conditions such as hemophilia always remember to show the genotype of the male and the female remember males are XY females are xx so you've got to always have that genotype written but then the allelic expression either the dominant of the recessive allele is written as a superscript okay so let's talk about first the females the different combinations of how those genotypes would be derived in the case of a female okay so remember a female that's XX right so this X chromosome may carry the dominant allele and let's say the other X chromosome also carries the terminal eel and this is the first possibility since this person has dominant alleles on both the X chromosomes right dominance going to code for normal so therefore this person is normal does not have hemophilia the second possibility is where one x chromosome carries the dominant allele there is the second X chromosome carries the recessive allele right so in this case always dominant allele will override the recessive allele so therefore this person is also normal but since this female carries one recessive allele she is normal but she's a carrier okay now the third possibility which is kind of not designated here but I'm gonna write it out here in pink the third possibility is again a heterogeneous combination where you have one dominant one recessive but I've just swapped it okay so the first X chromosome carries a recessive allele the second X chromosome carries the dominant allele very similar to this second combination here so this is also a heterozygous combination and since you have at least one dominant allele this female is also normal but since you're carrying one recessive allele person is a carrier okay and the fourth possibility is right here where both the X chromosomes carry the two recessive alleles right so in this case since there's no dominant allele to mask the expression of the recessive allele the recessive phenotypes going to be presented and remember the recessive allele codes for hemophilia so in this last case because of double recessive expression of those alleles this female would have hemophilia when you're looking at probabilities here which is kind of what I've written out here on the on the left so remember there's 1 2 3 & 4 different possibilities of female offspring in in terms of whether this person has haemophilia or not right one two three three of the possibilities of female offspring have they they turn out to be normal so therefore this is three-fourths of the females would possibly end up normal and not have haemophilia so 75% of the females in this excellent condition would end up normal with only one thought of the possibility 25 percent of the female offspring ending up with haemophilia okay so in this case for this female to have a sex-linked trait you would this female would have received recessive alleles from both mom and dad from the X chromosome from both mom and dad okay that's the only way that a female would have expression of a sex-linked trait okay now let's compare what's going on with male offspring okay male offspring are designated XY okay now this sex-linked trait is an x-linked trait meaning this the these alleles for this particular gene coded for only on the X chromosome but not the Y chromosome okay so there's really only two possibilities here okay so remember there's nothing related to the Y chromosome here this hemophilia is not coded for is is not a gene that is expressed on the Y chromosome so on the x chromosome here this could either be carrying a domina Leal in which case this male is normal or the X chromosome could have a recessive allele in which case this male would have hemophilia if you're looking at the probabilities here now the males have a very very different probability this is a 50/50 chance right 50% chance that the male offspring would be normal or 50% chance that the male offspring would have hemophilia okay this is a 50 versus 25 in the case of females so females have a much better chance of not exhibiting a sex-linked trait simply because females carry two x chromosomes and the other X chromosome can kind of compensate there is in the case of males the other chromosome is not an X chromosome it's a Y chromosome so that's why this the probabilities and end up being 50/50 for the for the males now again I want to reiterate for a male that expresses or has haemophilia notice it's only the X chromosome that can bring that can carry that recessive allele which means inheritance of haemophilia or any sex linked x-linked trait that is seen in a male offspring is really because it was transmitted or it was inherited from mom okay that has nothing to do with this okay there is the case of female offspring getting a sex-linked trait both mom and dad have to give the recessive allele to the daughter okay okay so now let's kind of look at a punnett square here so if you remember what we discussed on one of those previous slides let's look at mom here and mom's written across the top dad's written here on the left so this is the genotype for Mom so remember mom is an xx and it looks like one of the X chromosomes carries abdominal eyo the other carries a recessive allele so in this case mom is normal but since she carries one recessive allele she is a carrier right normal but a carrier in the case of Dad we've got this particular genotypic expression since that X chromosome is carrying the domina Leal and the Y chromosome carries nothing in the case of hemophilia dad is normal okay so if you're looking at our filling out this punnett square just remember you are filling your you are going to bring mom's alleles down the column okay and you're gonna take dad's alleles across each row okay and when you fill out the combinations you end up with something like this so let's suppose look at the offspring determine how many of them are males how many are females so I'm saying xx xx so those are both females and I'm seeing an XY XY here on the bottom so those are both males so it's a 50% chance of males 50% chance of females right and then let's look at the expression of whether this is an all offspring or if the offspring has hemophilia so if you're looking at this ok these are both dominant alleles so this person's normal you've got one dominant one recessive so dominant always overrides recessive so this person's also normal in the case of the male here this is a dominant allele so normal but in this case this male has a recessive allele so therefore this person has hemophilia right so let's look at the punnett square here and determine some of the probabilities you have some examples shown here in the box here on the right so let's look at all the offspring first so there are four different offspring possibility so what percentage of offspring would end up being normal well it looks like three of them would be normal out of the four so 3/4 so that's 75% or you could ask how many percentage of the offspring uh end up being hemophiliacs so that's one out of four so therefore 25% if you're just looking at the male's ok so that would be okay there's only two males right the other two are females so what percentage of male are normal well that's one out of two so that's 50% and again percentage of male that are hemophiliacs one out of two that's again a fifty percent the percentage female that are normal well actually that looks like that is a typo this should be two out of two there should be a hundred percent and the percentage of female that are normal but carriers okay so there this one's completely normal there's no recessive allele in this particular case you have one recessive allele one dominant allele still normal but a carrier so therefore one out of two would be a carrier let's see if I can fix this mistake here okay so let's see if I can do this all right so percentage female that are normal remember both of those are normal so this should really kind of say more like two out of two I normal right which is a hundred percent okay so that sounds that sounds better so I think that kind of wraps up this discussion of inheritance we talked about the differences between genotypes and phenotypes and we also talked about Domino Leos and recessive alleles we didn't quickly talked about inheritance patterns and how based on dominant recessive inheritance patterns you can fill out a Punnett Square and then the last thing we discussed was sex-linked inheritance and then you can also look at these fun of squares regardless of what type of inheritance patterns and determine probabilities of the expression of a particular trait or the expression of a particular either heterozygous or homozygous combination and so on and so forth so I hope this made some sense and that you have a little better understanding of these genetics principles okay thank you