Okay welcome back. This week we're going to start in on I've labeled unit three Heritability. Really this week, week three and week four we're really going to start talking about genetics. If you recall from the first week. The way I characterize or define the field of behavioral genetics is it's the application of genetic methodologies in concepts to the study of human behavior. And really, one of the challenges in putting together and taking a course on human behavioral genetics, is you really have to learn something about genetics, as well as something about psychology. So over the next two weeks we're going to really deal with genetics. Some of you will have a lot of background in genetics, others of you may not have as much. What we're going to do or what we have done is on the web page. We will give you links, there are actually some wonderful resources on the web for brushing up on genetics. If you don't have a background in it there are also actually some excellent Coursera courses on basic genetics that you might consider. But what I'll try to do over the next couple of weeks is to build for us the concepts in genetics and the methods that we'll really need to use when we, when we get into talking about schizophrenia and IQ later. I've labelled this first module Mendelian Inheritance. I guess that's a little bit of a mis-label. I'm going to assume that you know and, and most people do know the basics of Mendelian Inheritance. Although I'm going to start with Mendel here. I'm, I'm going to still assume that you know the basics of that from, from your previous education. Really, the point of this first module is to begin to build a vocabulary. And I, I kind of recognize it. Again, for some of you, you know this vocabulary already. In which case, you can just breeze through this. For others, it's going to be new. And it's going to seem very jargonny but don't worry so much about that. The when I, although it's a lot of new terms now, when we, when I start using them again I'll, I'll remind you of what they mean and we'll, we'll supply a glossary on the web page for you as well. Although I'm not going to go into Mendelian Inheritance, I'm going to start with Mendel. So the Mendel back when he published his studies of, of the pea pod in 1865 really I think one important thing to recognize is that what Mendel did was develop a mathematical model. For the inheritance of certain qualities across generations in the pea pods. And he studied things like the color of the pea pod, or it's form, or it's size and what not. And that mathematical model had various postulates. Each character he studied, and I believe it was seven or nine characters, each character was governed by two elements. And you inherited, or the pea pod inherited one element from each of its parents. And one element could dominate over the expression of the other. So for example, in this mathematical model which could make very precise predictions about transmission. A mother had two characteristics, two elements. And in this case, let's talk about whether or not the pea pod is green or yellow. And if a mother transmitted a green or a yellow. And it combined with whether or not a father transmitted a green or a yellow. You would get these four different possibilities. The green el, the green element here dominated over the expression of the yellow element, so this was considered a recessive characteristic. Certain terminology here. The term gene actually was not a term certainly that Mendel used. It wasn't really coined until 1905. We now call those Mendelian elements genes. Which are the functional units of inheritance. Actually not until next week, until we talk about molecular genetics, will I try to give you a definition of gene. It's actually a very difficult thing to define these days. But, these Mendelian elements that, that Mendel talked about, we now called genes. So we can talk about a gene for whether or not it is a yellow versus green pea pod. The alternative forms of a gene are called alleles. So for the pea pod color, the alleles here are Y for yellow and G for green. The genotype for a mendelian characteristic are the two alleles one inherits, one allele from the mother, one allele from the father. So the genotype is the pair of alleles for the color gene. Homozygotes have two identical alleles, a G and a G or a yellow and a yellow. Heterozygotes maybe inherited a G from the mother and a Y from the father. Or the Y from the mother and the G from the father. And at this point and in standard mendelian genetics, we consider the GY and the YG combinations as equivalent. Actually, as we'll see though next week in some cases they aren't equivalent. It depends on which parent transmitted. So we have genes, the Mendelian elements, alleles, the alternative forms of those elements, and genotype, the combination of the two elements you inherit at a particular, for a particular characteristic. We now know, and certainly Mendel would not have known this, the genes are located on chromosomes. Chromosomes are strings of DNA thread like structures that DNA packaged into protein. Again next week we'll talk much more about DNA. And these exist in humans within the nucleus of all our cells. We visualize chromosomes in alternative ways. And I'm going to take just one human chromosome, it happens to be chromosome 9. And look at different ways it's represented in the literature. First of all, we, this is a pair of chromosome 9s. So, one of this pair was inherited from that individual's mother, so that's the maternal 9. And the other pair was inherited from the father, so those are two different chromosome 9s. One inherited from the father, one inherited from the mother. The, the two alternative 9s are called homologous chromosomes. And you can see when they are viewed this way, they have kind of this striped pattern or banding pattern to them, and that's not how they naturally occur. What geneticists do when they want to visualize chromosomes is that they actually stain them. And what you get are, the stains actually are taken up in different regions of the chromosome. And that helps geneticist identify that it's this, this is a chromosome 9, and not a chromosome 11 or 10 or something. That's one way of visualizing chromosome 9. Two homologous chromosome 9s, one from a mother, one from a father. An alternative way of visualizing chromosome nine and you perhaps have seen this before is where a single chromosome 9, let's just say it happens to be the mothers chromosome 9, the one that came from the mother has been duplicated. In this case the, the chromosome actually looks kind of like an x, with a constricted point here. Here is actually there is only one chromosome 9, there are just two copies of it. Two identical copies here. These two identical copies are called chromatids. So this might be the maternally derived chromosome 9, and then somewhere else there's the paternally derived chromosome 9. The last way, and maybe the easiest way to, to visualize these is as what, what geneticists calls ideograms, where they're kind of a schematic, a figure of the chromosome 9. And so let's, let's look a little bit more closely at chromosome 9 here. And a little terminology that goes along with this. First of all these ideograms reflect the banding patterns that are used in identifying that this a chromosome 9 and not an alternative chromosome in the human genome. Some terms in, in terms of looking at chromosomes. Chromosomes have two arms, a short arm and a long arm. The short arm is designated the p arm. P is for, if you want a pneumonic for remembering it, p is for the French word petite, for small. And q is just because in statistics p plus, is complementary to q, so q is the long arm. P for petite, short arm. Q for long arm. The two arms are joined by a constricted point called the centromere of the chromosome. And the ends of the chromosomes, both ends, are called the telomeres. The, there are various landmarks along the chromosome, and there's kind of a nomenclature. And, and we'll see a little bit of this later when we, we, we actually look at molecular genetic data and schizophrenic. Where there, there's just a standardized nomenclature that's developed that kind of corresponds to the bands. So this is the 9p24.2 region and so on and so forth. On chromosome 9, so genes are located on chromosome. And one of the, the results of the human genome project is we actually know where the genes are now. We, we can precisely locate them. So turns out that the gene that governs your ABO blood type locus is located on chromosome 9. It happens to be located on the long arm of chromosome 9, and actually, we can locate it even more precisely at this particular band down here, 34.2, 34, I guess, 34.1, sorry. So genes have a particular location on chromosomes. That location is called its locus. Loci for plural. And again the alternative form of a gene at a particular location is called an allele. Now when you probably learned classical Mendelian genetics and the way we often illustrate is we, we, we maybe fall into thinking that there are only two alleles or two possibilities at a given locus. That is not the case there can be more, more than two alleles and there can be many more than two alleles at a given locus. The ABO locus actually illustrates that, there aren't two alleles at the ABO locus. Obviously there's and A allele a B allele and a O allele. Okay so petite short arm, Q long arm centromeres, telomeres, land marks that corresponds to the bands. Location of genes on the chromosomes. The human genome consists of 23 pairs of homologous chromosomes. Again homologous. One you inherited from your mother, the other you've inherited from your father. So here it actually is the chromosome 9s I showed you before. One from the mother, one from the father. The, the picture of a, of a, of the chromosomes, the 23 pairs of chromosomes in humans is called a karyotype. So, this is just a display of a karyotype of a human. So, there are two different types of chromosome. The first 22 pair are called autosome, these are the non-sex chromosomes. And they're numbered from one to 22. And the numbering more or less corresponds to the size of the chromosome. So chromosome one is a large chromosome, and chromosome 22 is a small chromosome. The ordering by size is not perfect because when they originally numbered the chromosomes, they were unable, because of the precision of the instruments they were using, unable to actually tell that chromosome 22 turns out to be a little bit bigger than 21. But that's a minor issue. For the most part, they are ordered by size. So chromosome one is going to have a lot more DNA, many more genes than chromosome 21 or 22. So the first 22 are the non-sex chromosomes or autosomes. The last pair, the 23, 23rd pair is the sex chromosomes. In humans, the sex chromosomes are either X or Y. Two Xs is a female, and X and a Y is a male. So in this case this is a karyotype, or the 23 pair of chromosomes for a human male. Each one of these chromosomes as I've mentioned before, but important to emphasize. Each one of these you have inherited one from your mother and the other from your father. So we have pairs of chromosomes. Humans are what are called a diploid. We have a diploid genome. Two copies of each of the chromosomes in the normal state. When we create a gamete. A gamete is a, is either an egg cell if you're a woman, or a sperm cell if you're a man. When we create a gamete, what we do is we actually transmit for each of the 23 homologous chromosomes one of the pair. And that if, let's say if you're a woman, you would have one of each of the 23 pair in your egg cell. And then a man would have one of each of the 23 in the sperm cell. And when those join together, then you get back the full complement of 46 chromosomes, or 23 pairs. The gametes though, the egg and the sperm cells, are called the haploid. Or they're in the haploid state, because you have half the genetic material. So, individuals have a diploid state of chromosomes. Two mem, two copies of each chromosome. When we produce egg or sperm cells, we do that by taking one of each and going into a haploid state. [SOUND] There are two cell divisional processes that are ongoing in which the DNA or the chromosomes are duplicated in your body. Only one of these that, that will actually be all that relevant for this course. The first isn't that relevant but I'll mention it, it's called mitosis. Many of the cells in your body, not all of them, but many of the cells are continuing, continuing to divide. For example, your skin cells or your blood cells continue to divide throughout your life. And the, the, that process of division is called mitosis. And it, it's the process by which you take a cell, and you duplicate the diploid set of genetic material in that cell. You duplicate it and produce two genetically identical daughter cells. So that's the ongoing process of cell division that takes place in your skin or your blood cells. What would be more important for this course is a second cell divisional cycle, which is called meiosis. Meiosis is actually, Mendel didn't know anything about meiosis, Mendel developed a mathematical model. The biological basis for Mendel's model is actually meiosis, discovered much later. Meiosis is the pro, production of a gamete, an egg cell if you're a woman, a sperm cell if you're a man. In that case you're going from a diploid state into a haploid state. So in humans, we start with 23 pair of chromosomes in the diploid state to produce a gamete, an egg or sperm cell. We go from 23 pairs to 23 individual chromosomes, one from each pair. A little illustration of meiosis here. This is a, a diagram, this is a simple organism undergoing meiosis. And I really only want to highlight a couple things at this point, things that'll be important to us later in the course. So, this is a simple organism, much more simpler than us. We have an organism whose genome consists of two pairs of chromosomes. The large one that's called chromosome 1 and the smaller one chromosome 2. And let's say the red ones came from that organism's mother, and the blue ones came from that organism's father. In this early stage of meiosis, these chromosomes actually duplicate themselves. So we're seeing the chromosome, we're visualizing the chromosome, in that second state I mentioned a little bit earlier. Where each chromosome has actually duplicated itself. And so you see two identical chromosome, chromosomes, those are called chromatids here. At this stage, what's happened is the homologous chromosomes have segregated into two daughter nuclei. In this nuclei, in this nuclei here. What's happened is the mother's chromosome 1 has gone along with the father's two. And in this one, it happens to be that the mother's chromosome the father's chromosome 1 has gone along with the mother's chromosome 2. At this stage when the homologous chromosomes segregate, the two chromosome 1s and the two chromosome 2s here, they do it randomly or independently. And it's that independent segregation of those chromosomes that is the basis of Mendel's law of transmission. The second thing that's important for meiosis here, and this we will come back to it, so I just want to introduce it to you here. We'll actually come back to it when we talk about schizophrenia is, you can see that there is been an exchange of material, here. So let's just look at this chromosome 1. So red is come from this organism's mother, blue from the father. The chromosome 1 here is now a composite of the maternally derived chromosome 1, and the paternally derived one. It has a small part of the father's chromosome 1. There was an exchange of the maternal and paternal genetic material. That exchange is called recombination. It's a phenomena that I am not going to talk a lot about now, I just want to introduce at this point. We will come back to it when we talk about the genetics of schizophrenia, because that phenomena is actually very important to mapping human disease genes, the phenomena of recombination. Later on it's, these then divide further, so we've gone from a state, a diploid state of four chromosomes, down to two chromosomes, these are the gametes here. So this first module, what I've tried to do is begin to develop some vocabulary that we'll begin to use. For some of you, again, this will be old hat. For others, it might be quite new. And what I'm going to, I'll try to do is as I use these terms again I'll try to remind you of the definitions I gave you here today. Next time we'll actually extend Mendel's models to try to deal with quantitative trait variation. [SOUND]. [BLANK_AUDIO]
