hi everybody in this lecture i would like to speak with you about mendelian genetics since the beginning of human history people have wondered how traits are inherited from one generation to the next kids look like their parents and their siblings and we were able to develop a lot of domestic plants and animals which are bred for useful traits by controlled matings it's all about inheritance the study of inheritance has two sides to the same coin inheritance is about similar phenotype but also about variation a union between a male and a female is well over 64 trillion genetic combination that's a big house if you want to understand the rules of genetics with such a huge variation however the field of modern genetics gave us the tools to understand inheritance rules there are rules that control inheritance and this lecture is going to simplify some of them for you so what are the goals that control inheritance one possible explanation of readity is the blending hypothesis the idea that genetic material contributed by two parents is mixed in a manner analog to the way that blue and yellow paints can make green that's one direction that you can take intuitively blending hypotheses makes sense in a daily life i will take my cat as an example all i know about is heritage is that it was born on the streets of the city of toronto i do not know anything about its genetic background now if you cross such a cat with another cat with unknown genetic background you will get a mixed phenotype something like that well maybe but you're going to have some phenotype from this cat and some phenotype from the other cat so the overall phenotype will be something in between an alternative to the blending model is the particulate hypothesis of inheritance the gene ideal pass a discrete heretable units genes to their kids for example here you have two options of color purple and white the f1 generation that came from a crossing between those two plants the hybrid in between the two is not going to have a light purple as compared to the parent it's going to have exactly the same color as one of the parent one way or the other up until the end of the 19th century if you would run a poll 99.9 of the people would say that the blending theory fit best with the rules of inheritance that's what you can see in nature people and in most of the farm animals and plants gregor mendel challenged the existing general understanding of genetics at the time his work when the pea plants which we used as a model made him to discover the fundamental laws of inheritance let's start with some definitions that will help us to understand mendelian genetics a trait is any characteristics of an individual each visible trait is called phenotype heredity is the transmission of traits from parents to their offspring hereditary determinants for traits are called genes alleles of different versions of a gene the combination of alleles in the individual is called its genotype individuals with two copies of the same allele how homozygotes and those with different copays of the same allele are heterozygotes an organism that is homozygote for a particular gene have a pair of identical alleles for that gene an organism that is heterozygous for a particular gene as a pair of alleles that are different for that gene gregor mendel during the middle of the 19th century gregor mendel an austrian monk and plant scientist study the principles of hereditary many think that mendel was a full-time monk and was doing the scientific work on the side as an hobby however that was not the case during the middle of the 19th century it became apparent to the policy maker in the center of europe that they must find a way to improve crops and animals the spanish or portuguese at that time [Music] both new animals and plants to europe from the new world and the austro-hungarian empire felt they are going to lose their superiority that they add up to this stage they recruited young people to monasteries which were operating as biotech high-tech the head of the program in bruno realized that one young person gregor mendel was not like most of the others first it came from a poor family all the others came from rich families but grego mendel was the son of a peasant farmer and in such poor families you cannot be spoiled so much you need to work hard for your goals no shortcuts gregor mendel was working differently it was very slow in his progress and for several years it did something that the others thought it is not important he was working on setting up his experimental system that's a very important and time-consuming stage of research when i did my phd work well i spent over two years just to set up my system just to develop the methods how to study the scientific problem so mendel went to the market and he got the different kinds of peace his first question he asked himself is well if i study inheritance i have to start with something with the constant property well it was not obvious at the time that the most important things to do if you want to study inheritance is not to start with courses but to set up your experimental system to make sure it is working works on it constantly and the same way and when you're doing the same experiments twice you're getting exactly the same result mendel devoted ears to create the reagent for his experiment and those reagents were mainly through breeding peace which are homozygote for certain traits so for each of the trait he made sure that if he crossed them to themselves the same property and only the same property would be observed either or a situation in which there is a choice between two different options but both together are not possible so gregor mendel made sure that he started his experiment with varieties that are true breeding homozygotes mendel tracked only those characters that vary in an either or manner one way or another and there is an other things that mendel did first he made the choice of the model that he want to use and here he decided to work on pea plants first because they are easy to grow in a small garden this is the garden that he was using very small well i mean if you want to work with goats cows that's not going to help you a lot so that's the gowden that he was using are two old pictures that probably are coming more or less from the time of mandel or maybe a bit afterwards and this is a photo from 1996. so making the choice of the model was based on the resources that he had around him that's a clever decision to make a model that you can manage we learned a lot from mendel's approach we learned that to make a model that you can manage you need to study organisms that are easy to find many organisms that we are using as a model well i mean there's an organism that you can find in the kitchen yeast that we can use for making bread is a very important model for many things including cancer fruit fly that grow well on rotten vegetable well i mean that's an excellent animal model to study genetics it was initiated by thomas hunt morgan he was the first one to use the fruit fly but that was a good idea to use an animal that you have it anywhere in your kitchen if you have some rotten tomatoes or potatoes or other type of vegetables mold that you can find on old bread were used also as a model mendel made plans to reduce environmental effect on his experiments the garden was in the corner of two wings of the building and it was quite protected from wind that can move poland from one planet to another he wanted to control the pollination of plants and using the location over here was quite important and there is another factor peas are coming in many varieties a lot of traits to choose from mendel started with approximately 34 traits but later he decided to concentrate on seven traits there are many resources about genetics that you can find in this website dna from the beginning and here you're going to see few animations which i picked up them from this website so let's go to mendel's experiment so this is gregor mendel he was working on pea plants because they are easy to grow they have many threads that distinguish strands of peace from each other and what he actually did in order to look for crosses in between peas with different traits is the following what you see here is a mature flower inside you can see the stamen which is the male sex part the stamen mature first and drop pollens inside the immature flower later on the pistol which is the female sex part matured and its eggs can be fertilized by the pond that land on the pestle so that's the way that most plants are being fertilized myself self-pollination the pistol and the stamens are formed the same flower but the mendel decided to control those courses by making sure that the pawns are coming from another plan that it shows so what he did in order to have cross fertilization of his pea plants he cut their stamens before they mature and dropped pollens and now it was in the position to take poland from other plants and to use them for the cross fertilization experiment that it did so in nature that would be outdoing they're picking up poland from one plant and moving it to another plant oh in many other cases the flowers are self fertilized but in those cases of course fertilization in nature is done by insects in most of the cases so by keeping track of the progeny from self fertilization and cross fertilization events regular mendel to study how pea plants traits are inherited pea plants have quite a lot of distinctive threats and he decided to work with seven of them let's go to his experiments with seed color so as i mentioned earlier regula mendel created purebred strains that when you self fertilize them you're going to see always the same trait so one of them was yellow when you self-fertilized yellow you are going to have only yellow phenotype when you self fertilize green plants you're always going to have green plants as their progenies so we start with a pure bread what he found is that when you cross between yellow and green you're not going to have yellow green progeny when it was crossing yellow and green all the progenies were really yellow like the yellow parent it was not something in between so it's not blending and that's what he had in all the other traits one way or another it was never something in between it was exactly like one parent so in crossing between the yellow p and the green p oh the f1 the progenies were yellow like the parent but when you take the f1 the progenies and you are making between them or you are doing self-fertilization and that's what he did i'm going to see something really really interesting green is back some of the second generations the f2 which of the progenies of f1 are green i mean it wasn't half green it wasn't yellow green it was green like their grandparents was really green color the green color reappear how we can explain this we can explain this in the following way the parents generation was homozygous they had two yellow alleles all dead two green onions a purebred green seeds plant f to green alleles and pure red yellow sage plant f to yellow alleles when you have fertilization only one allele from each p is involved so you're going to have always heterozygotes in this situation one allele is yellow the other layer is the green allele and the phenotype of detrozygot is based on the yellow a lil only so since all that zygote offsprings are yellow the yellow allele must be dominant over the recessive green allele now the green allele did not disappear its effect cannot be seen in the heterozygote but it is still there so what you have after all is the homozygote yellow is yellow and also the heterozygote as a yellow phenotype and only the homozygote recessive is green now when you're taking the progenies the f1 which are heterozygotes and you are crossing in between demo you can do self fertilization again one allele from each parent here you're going to have the recessive alleles here you're going to have heterozygote heterozygote and homozygote dominant and the green is big the green is back because the two recessive alleles are going to give you the recessive phenotype the green so when two heterozygote plants are being crossed the resulting progenies are going to have a a green progeny and majority are going to be yellow so the recessive phenotype is back this experiment was really the critical experiment in mendelian laws the experiment that i described for you are directly giving you two different important laws of genetics that came from mental experiments the law of segregation and the law of dominance about the law of independence assortment here mandalay to do some other type of experiments that will be described later so again in general the summary of the result of mendel here with the color of the flower trays is the flowing when you cross a plant with a recessive trait with true breeding parents which is purple and purple flower phenotype is dominant to the white flower phenotype all plants are going to have a purple flowers but when you have a cross between the f1 generation the white flower is going to be back mender's work was not just a descriptive work about dominant and recessive relationships there is much more into this throughout his studies mendel recognized the mathematical patterns of inheritance from one generation to the next mendel did something very very important he counted the plants with each phenotype he had real numbers of each phenotype counting is important it's not just as descriptive way of looking on recessive dominant but it's also about finding a special ratio in between the different traits the dominant and the recessive traits the ratio between the dominant versus the recessive on the f2 generation was three to one but that's wrong because mendel in his data never three to one yet something around three to one he had three point fifteen to one he had 2.84 to one so mendel said that although the data are not three to one the data are trying to tell him three to one this is a science many cases the data are not telling us the full story and the scientists need to understand the meaning of the data this is what statistical analysis is all about actually mental work represent the merging of a new scientific field statistics but still looking on the published data may give the impression that the statistical significance in mental experiment is too high based on the fact that the sample size which is not much more than thousand in most experiments sometimes it's less than thousand some pes and when you're looking on the specific ratio when you're using this level of sample size statistically some people said that well i mean it's too good to be true well after all experiments are done outside they can be affected by wind and other environmental factors but here again mendel repeated his experiments many many times but for the report it shows the experiment that are supporting the point he was trying to deliver the three to one ratio that's what scientists are doing all the time repeating their experiments several times getting the idea that they are getting the same type of direction but then in the publication they are using the best result which make the point clear this is a science and mandel was a real scientist mendel did not just describe his theory he also proved his theory with numbers he actually discovered the mathematical pattern of inheritance the pattern of inheritance was moving mathematically with a 3 to 1 ratio in the f2 generation it looked on the phenotype of the f2 and from here it was able to make a conclusion on the phenotype of the parents so mendel did the test course to understand the genotype of the parents and of the f1 and the three to one ratio in the f2 gave mandel a strong indication about the genotype of the parents so the three to one ratio was telling the big story about mendelian genetics this way it was able to go backwards and to determine what how the expected genotypes in the parents and what is the mathematical model which is involved with heredity the gene transmission i believe that if the only information we had for mendel was a descriptive work that would not make such a huge impact on genetics one of the reason that i think so is because the descriptive information about one phenotype that can be changed in the following generations which is part of mendel's theory was published before as a written description about an event that took place thousands years ago again the bible is a religious book but if you take the bible story as an historical evidence and if you add to the bible story today's scientific genetics here in goats you can see that levan and jacob's story is some sort of practical mendelian genetics in action overall jacob was able to switch a dominant phenotype into recessive phenotype the only way to do so is by making between heterozygotes and the bible jacob was able to do it quite quickly so he was able to find to choose the heterozygotes and to mate in between them in a way that it can get the recessive phenotype so uh how it can take place the shepherd can identify that or zygotes by some ways no ways to look for heterozygotes which have sometimes a distinctive phenotype then you can have a good sense for the outcome of certain meetings even without understanding the mendelian mathematical pattern so what i'm trying to say is that practically there is a chance that we were using mendelian genetics in some situations well we were quite successful in the last 10 000 years in developing strains of animals and plants so i believe that the practical mendelian genetics was out there well before mendel and according to the mendel's experimental design and the data chosen for the report there is a good chance that mendel understood the rules of genetics before we did is crossing experiments and his formal publication is moreover statistical mathematical formal proof of what he had realized in the years that he set up this experimental system started probably with heterozygotes initially and try to make them through breathing and you realize that is getting green from two parents which are yellow and trying to understand this may help him to come with the conclusion even before he was able to do the real experiment and there is a something else when we are talking about already tauri the idea of james was not clear at all but aristotle the greek philosopher thought that inheritance was not some sort of a spirit or emotion as others suggested but it's a physical coming from both parents well even here you can see that there is some progression towards mendel before mendel mendel's law of hereditary are usually stated as the law of segregation no blending one way or another the traits are discrete traits so what make them is a discrete unit engine when mandel crossed contrasting bread yellow and green seeded plants all the offspring were yellow green disappeared entirely when mendel self caused the f1 plants many of the plants add yellow seeds but summit green seeds so green is back it was not lost it is not back as yellow green but as struggling like the parent plants this is a huge finding the other law that came from mendelian experiments is the law of the dominance if the two alleles are different from each other in an organism then one the dominant allele determines the organism's appearance and the other allele the recessive alleles has no noticeable effect of the organism appearance again if the two alleles are different so this is the law of dominance in the f1 plants only yellow sets facto was affecting sets color in those hybrids yellow set color was dominant and green set color was recessive today we know yellow is a result of an enzyme that can make a yellow product fifty percent of the enzyme is enough to create a yellow color in the green sets of the layers of the gin are mutated so there is no active enzyme which is produced in those cells so the green is coming from the color of the chlorophyll that's really the general translation for molecular point of view and when we are looking on the genes that are involved with mendelian experiments and some of them were discovered and cloned and studied we can see that actually that's the case in all those cases so 50 of the wild type product gave you a wild type phenotype one functional allele is enough to give you a similar wild-type phenotype as to a little do i mean the fact that you have hundred percent of the product or 50 product it's not going to change the phenotype it's the same and only if both alleles are not active their product is not produced at all and that is the situation you will have an alternative phenotype here you can see the molecular nature of mutations and mutated form are simply not active as compared to the wild type so that's something that you can see here i mean the gene function it's mainly enzymes in one case you can see here it is a transcription factor that's but still fifty percent of the product is enough to give you the y-type phenotype so the wildlife phenotype is dominant over the alternative phenotype which is no gene product is made of the gene product is not active today we know about the genes that are involving medallion trait in general we are talking about enzymes and transcription factors which 50 of the wild type is enough to give you wild type phenotype mendelian genetics is relevant also to some cancers tumor suppressor genes are producing a certain factor which protect us from cancer they're recessive in their nature they protect us from cancer and usually you produce the tumor suppressor genes from both alleles that's the normal phenotype homozygote wild type so this is what we have in all our cells in general but if we are losing one allele for some reason one allele is mutated or inactivated the heterozygote cell as a normal phenotype muscle transformation is to take place from inactivation of one copy of a tumor suppressor gene due to the fact that half one out of the two wild-type genes is still there and the function of half of the protein is enough for the normal phenotype an evolving premalignant heterozygote cells can become cancer cells [Music] when the other allele is lost when both functional copies of the tumor suppressor genes that has been holding back the cell from its proliferation and the cancer phenotype are not active the cell is going to be transformed the loss of heterozygosity of suppressor can lead to the development of the cancer this is a classical mendelian genetics mendel the father of genetics he discovered the pattern that occurs as a layers pass from one generation to the next transmission genetics mental drug desegregation of genes and their appearance in the offspring as dominant or recessive traits men deduced that genes come in pairs and are inherited as distinct units one from each parent in general mendel came with a pattern pair to two singers two parents so mendel [Music] completed his experiments he wrote the paper a publication to summarize the information that he picked up from his experiments he read the paper twice february 8 march 8th in 1865 in the meetings of a natural history society and what next well nothing for many years mendel's work was ignored many people never knew of mendel's innovation well until after his death bender was a genius but maybe not a great presenter and a teacher his original publication failed to make others to fully understand what he had in mind i've read the english translation of mendel's paypal and found that it is very difficult to understand mandel for mendel himself on top of this his written publication was in german and many scientists did not read this language darwin for example at the copy of mendel's paper it was found in his belonging in a envelope that was never opened so darwin never read this paper that probably would give darwin some directions towards his own theory so after reading the original paper from the perspective of mendel's time i can realize how difficult it was in late 19th century to understand the abstraction of mental theory so one of the lesson that we can take from this is that it is not enough to come with great science that other cannot read or understand scientists need to use best method to present their work but reginald panet was a better teacher many years after mendel he came with a simple statistical presentation method to keep track of the allele distribution in the gamete with public square it is easier to understand what mendel had in mind so let's say that you want to start with mating between heterozygotes which have both the lids one is the yellow allele the other one is the green only first during the gamete formation the layers are going to be separated and this is according to the law of segregation that was coined by mendel now during the fertilization the union between the egg and the sperm you're going to have the following distribution of the allele again we have heterozygotes that have one allele that is responsible for the dominant trait the other allele is the recessive allele and during the fertilization you're going to have them to be joined together according to the gamete that is used so what you're going to have after all [Music] is the following one homozygote dominant allele then two heterozygotes and one homozygote of the alternative a little so what you're going to have here in terms of the phenotype the homozygote dominant you're going to have two heterozygotes and you're going to have one homozygote recessive the recessive homozygote is going to be green and the other three are going to have a yellow phenotype so this is the three to one ratio that was found by mendel on his experiment with one trait the three to one ratio is a critical number that can explain what is the mechanism that you can reach there so the three to one ratio is the critical information which is coming from mendel's experiment and here it is described in a clear way by the planet square so here again we have pearls in the parents to singers in the gametes and pears in the next generation this is the core of mendelian theory planet square is used to predict the genotypes and phenotypes of the offspring form across with punnett square it is easier to understand what mendel had in mind a gene pair defined each inherited trait parental genes are randomly separated to the gametes so that gamete contain only one gene of the pair and offspring therefore inherit one genetic allele from each parent when success unite in fertilization after mendel completed his work with peace he tried to extend his work to animals so he turned to experimenting with honey bees but he failed to repeat his rules of hereditary and one of the reason was that he was not aware to the fact that in bees the males are haploid the females is deployed but the male are haploid so you cannot see mendelian walls like we add in the peace and in many other organisms including us when male and female are deployed later in 1968 he was promoted to become the edit of the monastery and his scientific work largely ended as he became consumed by his increased administrative responsibilities mendel died on january 6 18 84 at the age of 61. in bruno for many years mendel's work was rejected ignored at that time most biologists held the idea that the blending inheritance is the right type of inheritance model people never knew mendel's innovations until after his death up until the end of the 19th century our understanding of genetics was very limited however since the mid 1600s or so with the discovery of the microscope we were able to understand that cells are the basic unit of structure in every living things since the microscope was invented scientists were able to see the cells by using some stains dies they tried many different dyes and in sub they found something in the middle of the cell that was stained very well for much of the 19th century scientists had no clue what is the function of this part of the cell that is stained so nicely so what is the first things to do when you see something but have no idea what it is all about well maybe to give this something a strong name and this name chromosome [Music] is actually cuomo zom which in our language can be translated to the colored stuff but those color stuff were found to be quite unique because they know how to dance and they know to dance not one but two different dances one in cells that are in the process to become eggs or sperms the gametes in different dance in all other body cells and this dance that is in all other body cells look like that [Music] scientists really wanted to understand what is the biological reason for the beautiful dances as we all know one represent mitosis and the other one meiosis a necessary process to make egg meat that was the discovery of teldo bovary towards the end of the 19th century suton and bovary carried out a careful observation of meiosis and they formulated the chromosomal theory of inheritance and with this theory of inheritance they found the pattern pear singers pear again the development of sperm and eggs start with a normal cell deployed the egg inserts are haploid singles and the union in between them bring back the diploidity the pair in the following generation so according to their proposal meiosis came with a pattern of inheritance that mendel observed mendel's rules can be explained by independent alignment and separation of homologous chromosomes at meiosis one me all this is a special cell division to make meat sperm and eggs why would regular mitosis be a problem in making meats well i mean we are diploids so let's say that the egg is diploid like the rest of our body sets and the sperm is also deployed and upon fertilization and i mean i'm going to have an embryo with foreign it's not going to be deployed but it's going to have four chromosomes in order to stay as diploid organism that the embryo will stay a diploid organism the egg will be applied the spam to be haploid and the union between the egg and the sperm is going to make a diploid embryo and that's exactly what meal this is about near this is about turning a cell which is deployed into an haploid cell so in the germ cells egg and sperm is essential there is only one copy of each chromosome pair so the meiotic cell division generate cells with half of the genetic material return from two sets of chromosomes to one set of chromosomes so it again pear singers pear that's the mendelian pattern as well two pears singers egg and spam pears in the embryo we can see it here in human being life we start with an organism which is to end deployed during me all this we are making eggs and sperms that are haploid fertilization bring back the diploidity in the embryo and then the embryo is going to stay deployed throughout mitosis and later on the meiosis is going to start the cycle once again so during the sexual reproduction sperm male reproductive cell and an egg female reproductive cells unite to form a new individual a process called fertilization so the sexually reproducing organisms are diploid to end 46 chromosomes in human gametes are formed from germ cells throughout the process called meiosis the gametes formed by myosis before they can be used for fertilization creating the zygote those gametes combine at fertilization to form a zygote which is deployed to an 46 chromosomes and one set of chromosomes come from applied egg which is 23 chromosomes and the other set comes from haploid sperm another 23 chromosomes here again per singles bear so me all these feet mentals quite well decades after mendel's death in the early 20th century based on the pattern of meiosis several scientists rediscovered mendel's research they probably communicated with each other do you remember the dead monk that was also talking about perv to singles pair like the new study by movie well each of them repeated mendel's findings and came to the same conclusion on their own william betson also translated mendel's paper to make it available for the scientific community that many of them are not reading german so the me of this is pretty much mendel's theory in principle but the correlation between mandel srit juan and meiosis in the pattern of pure singers pair it's not necessarily a full proof that they are indeed the same thing in order to prove the correlation is indeed representing the same idea you need to show that something else is applied from that correlation and can be explained by both set of data and that's actually the type of the scientific application that need to take place in order to nail down the idea that mendel's and bovary data are talking about the same thing and one of them is independent assortment that was one of the application that can help to understand whether bovary and mandela were talking about the same thing so we started with pair of single pairs correlation with an idea that meiosis could explain mendel as it is consistent with mental observation but as correlation is not proof they move further to prove the point with experiments this is type of application in science when data set was combined with other set of data so mendel did experiments with two traits and came with the principle of independent assortment so mender used the hybrid courses mating between parents that are both heterozygote for two traits to determine whether the principle of segregation held true if parents different in more than one trait the loved independent assortment is telling us that genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another so let's see how we can do such an experiment first we are producing an organism which is heterozygote for two threats how to do this one parent is recessive to both traits the other one is two bedding dominant of two traits the cross between the true blade dominant and recessive is going to produce an enterozygote for both the leaves and now you can use the heterozygote for cell fertilization if both alleles are segregated together for example here capital r and capital y are going to be segregated together and small r and small y is also going to be segregated together from this parent and that's going to be the case in the heterozygote the heterozygosity is in both genes but the connection between the capital r and the capital y which comes from here is going to be maintained so you're going to have capital y capital r and the other option will be small r and small y because it is coming from here when it is linked to each other in this case when you're doing self-crossing in f1 you're going to have four different options and you're going to have the following distribution means that you're going to have three to one ratio the three are dominant phenotype and the one is the recessive phenotypes for both phenotype that's one option another option is that genes are and why are totally independent of each other so when you get the combination of them they are not really linked to each other in any way if this is correct you're going to have a certain distribution that is going to be in the following way first you're going to have all the different options you can have link between the r and the wide are in the other wide and the small out with the wide small r with the small y so all those different options are here on this planet square they are in the y are not linked to each other and when you are calculating this you can count it you're going to say the following the dominant phenotype of both alleles is in the frequency of 9 out of 16 the dominant phenotype in one gene and recessive for the other gene like you see here three and here another three it's three to sixteen the recessive phenotype in both genes is going to appear 1 out of 16. and according to the experiments we have the ratio of 9 to 3 to 3 to 1 that means that this option of independent assortment is correct that they are in the why are assaulted in independent manner mendel's results really support this quite clearly this data is consistent with the prediction of independent assortment that we have during the separations of different chromosomes the principle of independent assortment in which a layer of different genes are transmitted independently of each other is supported by mental results with phenotypes of f2 offsprings from the hybrid crosses mendel's conclusion was that the two alleles for heretable characters separate segregate during gamete formation independently you can do the two traits experiment with parents of different phenotypes and genotypes as compared to what i showed you in the previous slide here in this animation that i'm going to show you we are going to start with one parent which is heterozygote for both genes and the other parent as the recessive phenotype in both traits to understand the principle of independent assortment let's consider one of gregor mendel's classic crosses in this cross mendel made it a plant grown from a round yellow pea to a plant grown from a wrinkled green pea the offspring of this cross appear in equal proportions of shape and color combinations the wrinkled green parent is homozygous for the recessive r and y alleles and produces only one gamete genotype the round yellow parent is heterozygous big r little r and big y little y for both genes and produces equal proportions of four organic genotypes the gametes fuse with each other in the cross to yield equal proportions of offspring genotypes note that in the gametes from the round yellow parent the dominant r allele is just as likely to be found with the dominant y allele as it is to be found with a recessive y allele in other words the r and y alleles behave independently of each other during gamete formation mendel referred to this independence as the principle of independent assortment today we know that independent assortment is explained by the independent alignment and segregation of non-homologous chromosomes during meiosis these identical diploid cells have just begun meiosis their progress through the cell divisions will illustrate the principle of independent assortment each cell is heterozygous for the shape and color genes one chromosome contains the dominant r allele and the homologous chromosome contains the recessive r allele another pair of chromosomes contains the dominant y and recessive y alleles of the color gene during meiosis the harmonicus chromosomes pair up and migrate to the middle of the cell notice that in one cell the chromosomes containing dominant alleles are lined up on the same side of the cell whereas in the other cell they are on opposite sides this arrangement in metaphase one determines which chromosomes segregate to which pole of the cell during division in the first case the dominant r and dominant y alleles end up in the same cell in the second case the dominant r and dominant y alleles end up in different cells the alleles of the shape gene have segregated from each other independently of the alleles of the color gene this is the basis of mendel's principle of independent assortment in meiosis ii the cells divide again notice that there are equal proportions of gamete genotypes one-fourth our dominant r dominant y one-fourth our recessive r recessive y one-fourth our dominant r recessive y and one-fourth our recessive r dominant y on average half the cells that undergo meiosis will produce the genotype shown on the left and the other half will produce the genotype shown on the right genes located on different chromosomes as in our example always a sort independently it's important to note however that genes located on the same chromosome generally do not the law of independent assortment gene for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another genetics is about application of basic principles but it's also about critical thinking about existing data besides putting mendel's rules and meiosis together scientists can do something else they can argue that if the connection between mendel and meiosis is correct in some situations mendel's rules must be violated and indeed every violation of mendel's goals led us to better correlation between mendel and meiosis how many traits mendel tested seven how many chromosomes you have in the pea plants seven interesting huh especially as we know that each of the tested trait is located on different chromosomes is this an interesting coincidence or very clever decision mendel did from the original paper i got the impression that mandel was initially interested in more traits up to 34 also there is a very good chance that mendel made scientific decisions i'm going to report now about the traits that have a simple pattern independent assortment that the gene happen to be located on different chromosomes and that's why we have this independent assortment and then they'll probably plan later on to do the other traits which deal with more complicated stuff this is science we are following mendel's footsteps since then by trying to understand first the basic rules and to move towards the complicated stuff later on and that's what mendel did it was looking on trades that are located on different chromosomes and in those type of threats well i mean you obviously have an independent assortment because the chromosomes are assaulted independently during meiosis so if mendel is right and if mendel and meoses are describing the same thing mendel independent assortment who must be violated for genes located on the same chromosome they are not transmitted independently of each other but together genes on the same chromosomes are not transmitted independently of each other and in this case mendel and bovary are talking about the same thing in those cases that the rule of independent assortment is going to be violated i can say this even more clearly meiosis fit mendel perfectly well only if in some cases the independent assaultnet go is violated we have thousands of genes on each chromosome if mendel was dealing with trait number eight or more yet to find that his independent assortment rule is violated he probably decided not to go there at that stage maybe to leave this to adele later and that's exactly what took place so we know about the seven traits from mandel and each of those threads are located on different chromosomes so it came with the independent assortment rule leaving the other traits that are working differently aside for now and if mendel is right the violation of independent assortment rule that we just discussed must be violated four jains located on the same chromosomes but are going throughout a genetic recombination during prophase one of meiosis may all this produce one random course over chromosome arm on average and if the genes are on the same chromosome but they are located a bit further apart from each other are not going to be violating the independent assortment rule although they are located on the same chromosome they are transmitted independently of each other in this case they are going to violate the violation of independent assaultment so meiosis fit mentals perfectly well if in some cases the independent associate is applied to genes located on the same chromosome well i'm sure that those of you that are planning to go to law school and to be lawyers have a lot of fun in this lecture and usually rules have exceptions and lawyers like exceptions however as biologists how should we deal with so many exceptions to the rule i would say that the exceptions to mendel's goals is the best things that is happening to those rules let's make mendelian genetics to be the reference of genetics any time the rules are violated we had some explanation to do any violation of mendel's rules help us to understand something new about the complexity of genetics this is the strength of mendel's work not the weakness as many suggested over the last annual years also other violation of mendel's rules different system of their sex determination in human and other mammals there are two varieties of sex chromosomes x and y female is xx male is x y family f two chromosomes of x male f one x one y so here sex linked inheritance is actually also based on mendelian rules and linked them to chromosomal genetics so when it comes to male genetics we need to know that we are haploid for the x chromosome and also for the y chromosome females is diploid for the x chromosome the x chromosome it's a large chromosome they have a lot of genes there and those genes act differently in males and females for their genetic pattern so here we don't have pair singles pair in mail another thing that makes things quite complicated is when you are looking on other animals here we have some changes in the sex determination many animals have different sex determinations the x zero sex determination system is a system that crickets grasshoppers coco chairs and other insects used to determine their sex in this system male have one x chromosome no y while female have two x chromosomes in birds well here the large sex chromosome which is the z is homozygous diploid in male couploid z is female so that's make things a bit more complicated when you're trying to do the analysis it's pretty much the opposite of what you have in human being in a birds the male is homozygote for the sex chromosome and the female is heterozygote in bees males are a haploid for all the chromosomes and female is diploid for all the 16 chromosomes and still the application of mendelian rules applies if you know what is the system that you are working with there is one more thing that we learn from mendel and this is a test course a tescos allow us to determine the genotype of an organism with a dominant phenotype but unknown genotype that's involved with causes of an individual with a dominant phenotype with an individual that is homozygous recessive for the trait so the test course is the genetic method we learned from mendel mendel the test process to understand the genotype of the parents so how we are using a test course to confirm a genotype when you have the dominant phenotype for two genes you have different options about the possible genotype so here you have a dominant phenotype for both alleles what is the genotype here so here you have different options for the genotype of the dominant phenotype of both genes so the test course to confirm the genotype of the dominant phenotype is based on using recessive parent the parent which is recessive for both alleles here you know that recessive must be recessive in both alleles so when you have recessive parent you know what is the genotype of this parent and if you find for example that the crossing between this dominant and the recessive p is giving you one to one to one to one ratio in this case you can calculate and figure out that we are talking about dominant which happened to be heterozygote for both genes so in test course a parent that is homozygous recessive for a particular trait is mated with a parent that has a dominant phenotype but unknown genotype the parent with the dominant phenotype maybe homozygote or heterozygote for the trait because the genetic contribution of the homozygote recessive parent is known there is only one option the genotype of the other parent can be inferred from the result of the test cause because the genetic contribution of the homozygous recessive parent is known the genotype of the other parent can be calculated here from the results that we have here and you can get the idea that in order to have this type of distribution you must have that the genotype of this dominant parent must be heterozygote for both gregor mendel challenged the existing general understanding of genetics at that time soy is welcome pay plans as a model it discover the fundamental law of inheritance mental genetics is powerful because of its simplicity but from here we can say that there are much more non-mendelian genetic complications mandel didn't know anything about epigenetics we also have codominance well cases when the phenotype produced is actually produced by both alleles and each of them is clearly expressed furthermore mendel chooses genetic threats in plants that are determined by only two alleles nature genes usually exist in several different form of multiple alleles you can have different mutations on the same gene and each mutation can make things to look a bit different furthermore many polygenic traits that are produced by the interaction of several genes when we are talking about a certain product which is produced by a pathway which is a system that consists of several genes its gene is going to have its effect but again mendelian genetics is our reference and every time they are violated we learn new rules in genetics on top of this mendel came with new scientific approaches his experimental design the way he dealt with his data created new standards in a scientific work and we still following his footsteps by applying those methods to our research mendel was the first one to come with a some sort of statistical analysis to tell that the numbers that are not exactly one two three ratio of telling us that it's one two three mendel was not aware during his life for the youth scientific contribution he made he died approximately 25 years before his scientific contribution was recognized