[Music] let's continue learning by talking more about inheritance a nucleus that has two pairs of chromosomes one from each parent is considered diploid in humans that number is 46 or 23 pairs we get 23 from our mother and 23 from our father we find the diploid cell in somatic or body cells the gtes or sex cells have only 23 chromosomes and that is called haid they are called haid because the chromosomes do not come in pairs but rather have a single chromosome that derives the pair of chromosomes we use the variable n to represent the haid number and 2 N to represent the diploid number for humans each egg and sperm are haid Nal 23 so that when the egg is fertilized sperm the resulting zygote has a total of 46 chromosomes this pattern of inheritance from diploid to haid and back to diploid is seen in all organisms that undergo sexual reproduction these organisms like humans are all derived from eukaryotic cells Gregor mle was an Austrian Monk and worked with pee plants in the mid to late 1800s in 1865 he published results of his experiment with pee plants and how their characteristics were passed on to offspring at the time that mendal was working the term Gene was unknown as was DNA and the structure of DNA mle used artificial pollination to obtain sperm cells in the pollen of PE Plants to fertilize the egg cells of another P plant he examined seven different characteristics as a shown in the table he consistently found nearly a 3:1 ratio of one plant to another for example looking at the seed shape he found the ratio of round to wrinkled as 2.96 to1 which we can Round Up to 3:1 let's look at another characteristic plant height mle took purebred tall plants and crossed them with purebred short plants pure bread means that tall plants only had the characteristics of tall plants and short plants only had the characteristics of short as did the parent plants of each group he wanted to see if he got all tall plants all short plants or a mix of short and tall when he crossed the pure bread tall with the pure bread short the result of this cross were that all of The Offspring or tall we know now that in P plants the alil or the version of the gene for tall plants is dominant over the AL for short plants a purebred or homozygous plant has the same alals for example a purebred tall plant would have uppercase tea uppercase tea and a purebred short plant would have lowercase tea lowercase tea a plant that has both is called heterozygous and would show uppercase te lowercase te to show these cross a punet grid or Square can be used as a tool you can see an example here the purpose of a punet square is to show all the possible combinations of genetic information for offspring of a particular trait if only one trait is examined that is a monohybrid cross while two traits would be dihybrid there are a series of steps when constructing a pent grid one choose a letter to represent the alals it should be the same letter for both the dominant trait is represented by the capital letter and the recessive by the lower case letter choose letters that make an obvious distinction between the uppercase and lowercase letters for example the letter B works well but not the letter O number two determine the parent genotype there are three possibilities homozygous dominant uppercase t uppercase t homozygous recessive lowercase T lowercase t or heterozygous uppercase t lowercase T it is very easy to determine the genotype of the short plant lowercase T lowercase T is that is the only way the trait of the short will be expressed it becomes more difficult with the dominant tradeit of tall as there could be two genotypes uppercase t uppercase t homozygous or uppercase t lowercase T heterozygous both will be expressed as tall the parental generation or P generation is what is being crossed The Offspring produced are called the first filial generation or F1 Crossing two members of the F1 generation will produce the second filial generation or F two number three the third step is to determine what gametes the parents could produce if the parent is uppercase to uppercase te the only gametes that can be produced are those with the uppercase t or the dominant trait the same occurs when the parent is homozygous recessive lowercase te lowercase tea only agar sperm with a lowercase tea can be produced if the parent is heterozygous uppercase t lowercase T they can produce two different gametes one with an uppercase t and with a lowercase teeth number four after the previous steps have occurred you can draw the punet Grid or the punet square the parents gametes are placed on top and the left side of the square next you fill in the squares by pulling in one Al from the top and one from the side to place two total oals in each box each Square represents one of two possible outcomes you can see in the cross between two parent that are heterozygous for height there is a 25% chance or one in four of being homozy dominant which is tall uppercase t uppercase t a 25% chance one in four of being homozygous recessive which is short lowercase te lowercase te and 50% one and two chance of being heterozygous uppercase te lowercase T which is also tall it is important to remember that this shows probability it does not mean that if one plant is short the others have to be tall when we look at plants specifically it's important to understand their Anatomy as it shows how each plant can sexually reproduce flowering plants like pea plants produce pollen which carries the male genetic material in addition to that flowers contain structures called ovaries that house the female genetic material the transfer of the genetic material from the pollen into the ovary will result in sexual reproduction and create a new seed that can then grow into a new plant of the Next Generation the process of pollen moving from one flower petal to another usually requires another organism like an insect to be a pollinator take a bee for example it moves from flow to flow taking the nectar and also collecting some of the pollen from one flower and dropping it off to the next this can support the cross-pollination of one plant to another plant and can also support self-pollination if pollen from a plant enters the ovary of the same plant self-pollination usually results in less genetic diversity compared to cross-pollination it is important to understand the difference between the Le genotype phenotype hom zygus and heterozygous some of which we have already mentioned on the previous slides an alil is a specific form of a gene and differs from other forms of the same gene by a few base pairs for example there is a condition where a person isn't aable to see any color this is not color blindness which is a Sex Link disorder discussed later in the video the condition is called a chromatopia and people with it cannot see color because they are unable to produce the protein transducin in their retinas you can see an example here based on these two renders of the same image this is caused by a single base pair difference between the most common Al with a c at position 235 and the rare mutation of a t at position 235 this shows two different versions or alals of that Gene a genotype is a symbolic representation of a pair of alals usually using letters for example uppercase t uppercase t lowercase T lowercase t or uppercase t lowercase T genotype are always expressed with two of the same letters that represent the same gene and the alals that make up the genetic code for that Gene homozygous means you have two identical alals either both uppercase or both lowercase uppercase t t is homozygous dominant while lowercase TT is homozygous recessive heterozygous refers to having two different alals uppercase t lowercase t a carrier is an individual who has a recessive Al but it does not have an effect on the phenotype which we will continue to discuss throughout the video the phenotype is the observable trait of an organism based on the genotype in other words the phenotype is what you see for example in a plant with a genotype of uppercase te uppercase te or uppercase tea lowercase te you will see the phenotype of tall plants because there is at least one dominant alil present in each genotype if the genotype is lowercase te lowercase te the phenotype is the short plant because it only has a recept exessive short alals there are some phenotypes that can change due to environmental factors and others that are controlled by genetics alone phenotypes controlled by genetics alone include your blood type environmental factors cannot change that an example of a phenotype produced only by environmental factors may be learned behavior such as birs learning new songs an example of a phenotype that may be due to a combination of genetics and environment is height a person may not reach their maximum height if they do not have the proper nourishment of obtained from their environment we have used the term dominant and recessive a few times so far in this video let us go a little deeper into what these terms mean a dominant alil is an alil that has the same effect on the phenotype whether it is with the same alil or a different alil if the dominant alil is present it is what is expressed in our example of PE Plants and height if The Offspring have two alals that are both a dominant Al uppercase t uppercase t the phenotype is tall which is the expression of the dominant if the plant has two different alals with one being dominant and one being recessive uppercase t lowercase T the phenotype is tall as well which is again expression of the dominant alil the recessive alil only has an effect on the phenotype when there are two recessive alals and no dominant alil present lowercase T lowercase T this sums up what the concept of dominant is all about dominant alals are always expressed when they are present and the recessive alals are only expressed if there is not a dominant alil present present which would mask through recessive alil every time sometimes organisms can express their phenotypes differently depending on the environmental factors present this is called phenotypic plasticity as an example some birds can activate genes to produce more Mal taste when their diet has more grains and less insects while other birds can modify their foraging behaviors depending on the types of food available in either case changes in the environment are directly impacting the genes that are silenced or expressed in the organ M impacting phenotypes phenology is a term used to describe cyclical events such as food availability which can provoke these changes within organisms phenotypic plasticity can generate changes in several ways through physiology such as the enzyme example and behavior such as foraging Behavior another way is morphology one example is the freshwater snail fisa vergata the snail normally has an elongated shell but when its Predator the bluegill fish is present a phenotypic change occurs the genes are expressed slightly different causing the shell to be less conical and more rounded and shorter this makes it more difficult for the bluegill to crush this is not considered a mutation as the genotype does not change the snail still has the same alals but it is able to silence and express genes in different combinations to change the shape of the shell there are many recessive genetic conditions which affect organisms in humans one disorder is phenol ketonuria or p KU a recessive disorder can occur even when both parents do not have the disorder but they must be heterozygous for the disorder meaning they must be carriers PKU is caused by a mutation in the autosomal phah Gene which results in low levels of the enzyme phenol alanine hydroxylase this enzyme is necessary to convert the amino acid phenol alanine into tyrosine phenol alanine is toxic and can build up in the brain and impair development of the brain which is why converting it into tyrosine via the enzyme is so important individuals who suffer from PKU do not create this enzyme and therefore have no way to break down phenol alanine when diagnosed at Birth modification in diet can prevent the impairment children affected by PKU must have diets that limit phenol alanine and will need supplements to be sure their diets have enough protein looking at the pant grid here you can see that both parents must be heterozygous for the mutation and while they do not have PKU disorder themselves they are carriers there is a 20 5% chance that their offspring will inherit both recessive alals and have PKU these disorders are called autosomal recessive disorders because they are caused by recessive alals autosomal means that the disorder is found on the first 22 pairs of chromosomes and not the sex chromosomes other examples of autosomal recessive disorders in humans include albinism cystic fibrosis CLE cell disease TX disease and phemia all of which are found on different chromosomes and have different impacts on the the body a gene pool is all the genes available to a breeding population and there are any number of alal of a gene that can be present in the gene pool but an individual only inherits two of those alals we have discussed only two possibilities either dominant or recessive but genetics is not always so simple sometimes there are three or more alals for a trait such as in blood type this will be discussed on the next slide our immune system has genes called HLA genes and some of them have dozens or even thousand thousands of different dels this is beneficial to use when you think of all the different pathogens our bodies need to fight single nucleotide polymorphisms or snps called Snips occur when a nucleotide of the genetic code like C is not found where expected and at that location is instead a different nucleotide if this change is found in part of our DNA that is a coding section it could be that a different amino acid is coded for which could change the structure and function of the protein that is translated one example of this in humans is the ability to taste bitterness this is important to survival as many toxins are bitter and the ability to taste this will protect the individual from consuming the toxic substance the molecule PTC or phenol thiocarbamide is a bitter substance people have one version of the gene t2r 38 can taste the substance this Gene encodes for a protein taste receptor 2 number 38 which allows a signal sent to the brain for interpretation in order to taste PTC only one functioning Gene has to be present because there are several different Snips of this Gene there are multiple phenotypic outcomes which include some people being able to fully taste some people can intermittently taste and others who cannot taste it at all it is common for biology classrooms to have their students try PTC paper to see what type of phenotype they possess the system of blood typing is an example of multiple alals be careful here as there is still only one gene that codes for blood type but there are more than two Al possible while the blood type system in humans has three alals there are six possible genotypes with four possible phenotypes while blood type demonstrates multiple alals it also demonstrates co-dominance we use the letter i uppercase and lowercase to represent the multiple alals and we attach superscripts to distinguish between them uppercase i superscript uppercase a uppercase i superscript uppercase B and lower uppercase i uppercase i superscript a is used to represent the AL that produces a protein called type A antigen which gives the person type A blood uppercase i superscript b is used to represent the alil that produces a protein called type B antigen which gives the person type B blood and lowercase i is a recessive alil that produces neither a nor B antigen giving the person type O blood a person with two uppercase eyes and superscript A's or one uppercase i superscript a and lowercase I will give the phenotype a blood a person with two uppercase Eyes Two superscript B's or one uppercase eye superscript B and lowercase eye will give the phenotype B blood two lowercase eyes will give the phenotype O blood when the antigen for A and B are both present codominance will be evident and a new phenotype will appear type A blood you will notice that the an anen on each cell is always opposite the type of antibody that is in the bloodstream this is because when an a antigen and an a antibody get together they end up connecting and clotting which is a protective measure built into the system in case any form blood enters your body for this reason it is important that if you were to receive blood from a donor you need to receive it from a blood type that will not clot with the antibodies present in your bloodstream this makes some blood types great for donating light type O blood because there are no antigens present than on the blood cells there is no way for it to clot with any antibodies making someone who is type O blood a universal donor [Music] [Music]