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Introduction to Genetics
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0:04
so we are going to start with chapter 1 introduction to genetics this chapter has a few things that you're going to have to study and know but mainly it's an introduction to the course and to the textbook so I will point out a few things that you'll have to memorize and really know but it's not a very long chapter a very long lecture now all of the chapters begin with what I call a "vignette" which is a little story typically has to do with a certain gene
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or a certain allele of a gene mutation that causes some phenotype or some interesting thing and the chapter 1 vignette is called "Albinism among the Hopis" and the vignette will answer the question how does the Hopi culture contribute to the high incidence of albinism among the Hopi Tribe so there's a story about it and you have to know the story what the gene is and what the story is for each of these there are a few that aren't specifically about
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certain genes but you need to be able to say in two or three sentences the the "gist" the main important stuff that's in the in the vignette so as you're reading them I would try to you know summarize it as concisely as you can so that when you go back to study you don't have to read them all over again but the vignettes are going to be your responsibility. So chapter one is partly about making a case that understanding genetics is important and I think it's
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hard to to argue that that genetics is not important in today's society the technology is moving along at such a pace if you don't know any genetics you're you're going to be a little bit at a disadvantage and the way things are going and so you probably know a little chromosome theory which states that genes are located on chromosomes and chromosomes are passed from parent cell to daughter cell during cell division and that those genes encode
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proteins you'll remember transcription and translation is what gene expression is, so when genes are expressed there are certain proteins that are made from those genes and they create different phenotypes they're responsible for all kinds of phenotypes in this slide you have bone structure of the hand for example so you have a series of genes a lot of genes that are that are contributing to correct bone structure of the hand and then certain
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mutations that could lead to a deformity shown in the bottom of a part a in this picture then in Part B you have a chromosome five it shows the location of some genes that are responsible for certain phenotypes and remember there's always a normal copy of that gene and an abnormal copy so a normal allele and a mutant allele so when we talk about an allele for dwarfism what we're saying is if you have the normal version of that allele, you have a normal height if you
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have a certain mutation of that allele then you have dwarfism so that the alleles are typically named after the mutation phenotype so a dwarfism gene is something it's really they're really talking about an allele where there's a normal allele and a dwarfism allele of the same gene and so anyway these have been mapped to different chromosomes they're showing chromosome five here and when there's a bracket it means they don't know exactly where the the gene
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maybe is but they've narrowed it down to a certain section we will talk later on about what the stripes mean on the chromosome you may recall that the center point of the chromosome the "primary constriction" is called the "centromere" so that's right here that's the centromere shown in gray but anyway we'll be talking more about that as we as we go along in the course we will talk a little bit about embryogenesis and development although that becomes a
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pretty specialized area of genetics if you study the genetics of development and embryogenesis but one thing that's interesting about about it is that as we studied more organisms more and more organisms what we realized is that it's not what genes well it's not only what genes are in an organism because a lot of organisms have very similar genes even fruit flies and humans have a surprisingly high proportion of genes that are pretty much
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the same but it's not what the genes are necessarily but how they're regulated so in the picture you have a Drosophila embryo that's been stained for the expression of Hox genes Hox genes set up the segmentation structure of the embryo and so you see these stripes there's two different genes being expressed in different locations so the blue stains one type of Hox gene that's being expressed in these alternating stripes and then the red is a different Hox gene
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and so the and then the white means no no expression of those genes now every cell in the organism has a copy of every gene but not every cell is expressing those genes all the time so gene regulation means the decision that a cell makes regarding what genes are going to be expressed in that type of tissue or that type of cell; when those genes will be expressed and when they will not be expressed; and at what level they'll be expressed because a gene can be
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expressed you know at a low level to produce a small amount of the protein product or it can be it can be heavily expressed to make a higher level of protein product so gene regulation is really involves a lot of aspects of the cell making decisions about what what gene to express, how much, and when. Now, good or bad, genetic genetically engineered genetically modified crops are a huge part of our food supply we don't know to be honest what the
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long-term effects of eating GMOs is going to be but we're basically we're the experiment so we'll find out I suppose and certainly it's led to people going you know to kind of an organic movement and you could certainly argue that that's at least safer or less risk I guess you could say we don't really know what the risk is for GMO crops but it has allowed us to produce plants that wouldn't be able to grow in drier environments to increase the food supply
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and so there are good sides to it we just don't know what the health effects are and then in in pharmaceuticals you have for 40-50 years we've been producing human recombinant human insulin human clotting factors for hemophiliacs growth hormones and a lot of vaccines and such are produced by recombinant DNA technology so there's good and bad there's definitely advantages and risks to to genetic technology, and being able to understand the genetics is certainly
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an important part of being part of our society now there's basically three you do need to know these the three areas of genetics three fields that your book lays out for you is transmission genetics which is Mendelian genetics molecular genetics which focuses on the biochemistry of the DNA and the RNA and the protein for example and population genetics which overlaps with evolutionary genetics and the genetics of groups and so we're going to start
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the course with fundamentall transmission genetics starting in chapter 3 and then we start with molecular genetics around chapter 8 and then we only do one chapter with population genetics in one lab so it'll mostly be a pretty even split between the transmission the fundamentals of transmission genetics and molecular genetics there are six commonly used model organisms in genetic research and you do need to know these you do need to
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memorize the names common names and scientific names and I'm going to pronounce them for you because the use of the language in science is one way that people judge you and I would want you to be using the correct pronunciations if you for some reason had to pronounce these in front of somebody who knows the correct pronunciation you want to show them that you're at a certain level of your education with with regard to these so I'm going to pronounce these for you and just listen
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closely and see if you can understand what I'm saying so the first one is the fruit fly is Drosophila melanogaster it's not too hard "b" is Escherichia coli or E. coli but Escherichia if somebody pronounces the whole thing that's what they're saying Escherichia coli but a lot of times we just say E.coli that's a bacterium "C" is pronounced Caenorhabditis elegans it's the C is soft so you say Caenorhabditis not cane-or-ab-ditis
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Caenorhabditis elegans we often say C period elegans for short. Arabidopsis thaliana that's the thale cress or mustard plant Mus musculus that's an easy one that's the mouse and then Saccharomyces cerevisiae the baker's yeast and these are the six top model organisms that your textbook author picks I would say that's a good pick nobody would really argue with these six being the top six you could add a few more there could be maize corn would be maybe number seven or maybe a zebrafish
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but these are good solid six model organisms that scientists wouldn't argue with, have been used heavily, and are the six that we're going to highlight throughout the course. So why do we study model organisms? I mean on some level we study them just to understand how genetics works in different organisms just for general knowledge but ultimately when we study them we're we're looking for mechanisms that are in common with human we're either trying to
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develop drugs ultimately or trying to develop crops or trying to look for cures for disease so in applied science we're looking for things that we can connect to something similar in humans so for example zebrafish which didn't make our top six model organisms but would certainly be in the top ten zebrafish have been studied and one example just kind of a simplistic example is that the melanocytes in zebrafish express a pigment that's it's
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not really black it's dark blue and in there's a mutant for that gene that produces an orange coloration and it turns out that that that gene is one of a couple of genes that produces pigmentation in humans so pigments are a combination of usually several pigments to give you different shades and different levels of orange brown black are typically your mixtures that you have and so you have normal zebrafish have normal alleles for the gene for
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that pigment where the gold mutant is the same the gene has a mutation in it and it gives you this golden color so it translates to a mutation that you would see in somebody with red red hair red pigmentation in the skin or really more orange but we say red and then the normal pigmentation would be like the normal zebrafish would relate to the normal coloration of the other individuals in the picture so now what we're saying is though that the things
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that you study and one organism can translate to the same type of gene and in other organisms. So at least ten thousand years ago maybe more we have evidence that farmers were using the concepts of transmission transmission genetics, and what I mean is they were doing selective breeding, animal domestication, artificial pollination of crops and because these require manipulation of sexual reproduction they are technically
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practicing you know they were practicing transmission genetics or the principles of Mendelian genetics you might call it common sense if you want to have a good group of a good herd of cows cattle then you're gonna pick your strongest bull and your strongest cow female and you're gonna put them together in a pen and try to make sure that they mate together so that you get the strongest calves that you can get so but but this is manipulation and it's been happening for
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thousands of years and so in that sense humans have been doing transmission genetics for at least 10,000 years maybe more but we really start "genetics" as a field as a field of science can probably only claim to go back a couple hundred years so even though there are elements of Mendelian genetics in agriculture to go back ten thousand years typically we go back to you know the 1800s something like that before the 1800s there were concepts of heredity going
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back even to Aristotle and but nothing was ever you know proven there was really no evidence or experiments there were different concepts a couple that are presented here and you'll read about them in your text one is pangenesis this idea that things they called "humours" just kind of like liquids maybe were drawn at the moment of you know delivery of sperm or release of egg that these things would be drawn from all parts of the body and they carried the traits from
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all parts of the body and then they would go into the sperm and then the sperm would be released or they would go into the egg and the egg would be released and that led to the formation of the zygote the fertilized egg and so pangenesis involves this sort of concept of liquids kind of coming together into the into the gametes and carrying the traits from all parts of the body into the gametes and of course that's wrong and and what sort of overlaps with the
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pangenesis concept a little bit is the concept of blending inheritance the concept of inheritance of acquired characteristics which you may have heard of in a "Lamarckian" discussion from an earlier biology class but these these concepts of course are wrong but they were floating around you know for hundreds and hundreds of years even before the dark ages and so they were pretty well entrenched by the time Mendel came around even though there
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really wasn't any evidence (I would argue) for it and what eventually was shown is that the the theory that is correct is called "germ plasm theory" but it wasn't possible to understand germ plasm theory until you could understand really almost until you could see chromosomes under the microscope so almost 1900 before you could really see that but the germ plasm theory says that there's a special set of tissue that carries the same genetic information as the rest of the body
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although only half the amount of genetic material in each sperm or in each egg but that that those are the cells that form the zygote that nothing is drawn from the rest of the body but those are sort of the representative cells for sexual reproduction and that's correct so you remember from meiosis that sperm and egg carry each carry a set of human chromosomes and that when they fuse together that forms the zygote which is the first cell of the new individual so
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that's germ plasm theory but you had all these other ideas the pangenesis the blending the inheritance of acquired characteristics and also you have this other wrong ideas the concept of preformationism which is a very famous drawing of a tiny little man the homunculus is a tiny perfectly formed man or woman I suppose but it's always shown as a man that's inside of a sperm so in this drawing it kind of indicates the importance they thought that the
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sperm had, the sperm carries, this was an idea like I said prior to up to but prior to the nineteen hundred mark where they thought that the maybe the sperm carried a teeny tiny little man and then when the sperm is delivered into the uterus the uterus provided nutrients to grow that little man bigger and bigger and bigger and that's how, that's where babies come from, so I guess there could be a girl in the sperm... but anyway of course that's wrong you know we know
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that's wrong so you have these I mean what seemed now to be strange ideas but those were pretty well I mean people believed those so you put the real beginning of genetics as usually starts with Mendel and he's in the mid-1800s so up until then you've got a lot of strange ideas floating around but by the time Mendel came around you already had a concept of cells and cell theory because that came around in 1839, so you've got that, but you really don't
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have chromosomal theory you don't know at that point he didn't know anything about chromosomes, he didn't know about genes, he didn't know about meiosis, so you're still I would say kind of working in the dark, if you were Mendel, he still didn't have much to go on, and it's what's interesting about Mendel and we'll learn about Mendel in chapter 3 is that he was working at at the same time as Darwin I mean virtually the exact same time and they published at close to
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the same time and and one thing about Darwin's work is that it had a terrible explanation for inheritance. If Darwin had had a better understanding of inheritance you know that that his work could have gotten more acceptance I think but he didn't have any real good understanding of inheritance and and Mendel wouldn't publish until 1865 and even when he did publish nobody really understood what he was trying to say because it was so different from those wrong ideas that they believed in.
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But I put a crown on Mendel because he's typically called "the father" (not the king) but the "father of genetics" so a lot you know for the most part we really mark 1865 as kind of the beginning of modern genetics as a field. Now like I said in 1900 when you start in 1902 actually when you can start to see chromosomes under the microscope and in 1900 when three scientists separately repeated Mendel's not the same exact experiments but very similar concept of experiments
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you have typically what's called the "rediscovery of Mendel's work" so in 1900 DeVries Correns and Tschermak individually - they weren't working together - individually did similar kinds of experiments you may remember the monohybrid cross the dihybrid cross those types of experiments and each of them thought that they had come up with something brilliant which they had but unfortunately they found I guess unfortunately for them they found
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Mendel's publication and that means in science you have to give credit to the first person who discovers something but it's called the rediscovery of Mendel's work because it seems like in 1900 the rest of the world was ready to understand what Mendel was talking about and very quickly after that you have Sutton and Boveri which did not they did not work together but they individually described the chromosome behavior of cell division and this laid the basis
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for what is commonly called the chromosomal theory of inheritance so look chromosomal theory of inheritance is important it says that chromosome are...that genes are located on chromosomes and chromosomes are passed passed from parent to...parent cell to child or to daughter cell so the basis of inheritance of the traits that are encoded by those genes.
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Now in 2001 maybe 2003 you have the completion of what's called the Human Genome Project and we'll talk about the Human Genome Project in chapter 15 but that was really just the beginning of the modern age of genetics so this picture shows how we used to do DNA sequencing which looks really highly technical but now it's even more advanced but when you have the discovery or the sequencing of all the human chromosomes, you really...I mean that was
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just the beginning and in 20 years what we've accomplished from that time till 2017 or almost 2018 is going to amaze you I think so the speed of technology in the field of genetics is just like any technology is just increasing alright so what are the things you need to know? what you need to know from chapter one is the wrong concepts of inheritance so the preformationism the pangenesis the blending the inheritance of acquired characteristics you need to know that
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germ plasm theory is part of the correct concept of inheritance you need to know the names of the six model organisms scientific names and common names you need to know the three fields of genetics transmission population and molecular but then you also as sort of a what you should know coming into the course is listed here so these are things that you already need to know number one basic structure and function of prokaryotic and eukaryotic cells what
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are the rules that govern the cells the energy flow the materials flow through the cells gene expression which is really part of that but I've listed it separately here gene expression is just transcription translation just the general concept of how genes are expressed cell theory which states that all organisms all life is made of one or more cells the cell is the smallest unit of life and that all cells come from
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other cells by cell division you need to know the relationship and the definition of genotype and phenotype you need to know your basic cell division especially your mitosis I will not spend very much time going over mitosis I'll spend a little more time on meiosis you'll have a lab on that and then the basic rules of evolution so if you're not you know fundamentally I mean in a general sense understanding these things and you're gonna be lost in the class so make sure
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you have these basics if you need to brush up that's you know that's certainly fine there's tons of resources online Khan Academy you know all these things that you can you can look up yourself but just make sure you you feel pretty comfortable with these things before you get going too too much into this course because I want to make sure that you're successful and I want to make sure that you have you know the right foundation
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