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Video transcript

OK, so as scientists and as psychologists study gene and environment interaction, they're really beginning to get as specific as identifying the particular genes which are regulating our behavior. And this gives rise to an entire new field of science called molecular genetics. And molecular genetics as a field is a science that looks at the actual molecular structure and the function of genes. So we're actually looking at the segments of DNA. And it was actually around the 1950s that James Watson and Francis Crick helped discover the structure of DNA, which gave rise to really a whole lot of brilliant discoveries. And one such discovery by Crick, by Francis Crick, gave rise to what we call the central dogma of molecular genetics. And the central dogma of molecular genetics essentially just says that segments of DNA called genes-- so a segment of DNA called a gene-- codes for RNA or ribonucleic acid. And the little units of RNA called codons are going to code for one of the 20 amino acids. So this is an amino acid. And at this point, it's becoming a little bit more of a biology concept. But these amino acids that are being coded for eventually become the building block of proteins. And it's these proteins that are being created that actually function in our body. So think of enzymes, which are proteins that speed up reactions in our body. Or you can think of the proteins that determine whether or not a substance can cross the different membranes inside of a cell and on the outside of a cell. And there are many different types of proteins in our body. But the point is that proteins kind of form the intermediate point between genes and our behavior. And I'm using the word "behavior" because in psychology that gives us a really nice, broad reference to our body's functioning and our response to the environment. So the central dogma of molecular genetics really puts a heavy emphasis on the role of DNA in really determining all the outcomes of these proteins that cause our behavior. But actually subsequent discoveries, especially those in this molecular realm, have caused us to reconsider the relative importance of DNA sequence-- so our gene sequence-- in determining the function. So as an example, think about steroids, which are hormones. And you can think of that as an environmental factor. And so you can think of the steroid testosterone. And so we've heard that steroids travel between different parts of our body to elicit responses. But those responses are actually the activation of genes to produce proteins. And if we want an example that's even more environmental, we can think of a stimulus outside of our body like pheromones. And pheromones really do the same thing because they're exciting the brain and they're causing a response inside of us. But that response again essentially is the turning on of genes to make these proteins that are going to form a function in our body. But if you think about it, in both of these cases the central dogma is kind of being flipped over because where at one point we put a really heavy deterministic emphasis on the DNA structure-- so the gene structure-- in determining the protein that causes our behavior, now we're actually shifting that determinism outside of the DNA sequence a little bit. So these phenomena are going to introduce us to the idea of gene regulation. And this idea of gene regulation becomes really important to our discussion of environment, and heredity, and behavior. So there's kind of this entire modulatory world to genetic expression. And I say modulatory because the gene expression is being modulated by an environmental factor. But one of the greatest achievements in clarifying these modulatory factors has been the mapping of the human genome. And so in the last two decades, scientists have mapped our entire genome, which accounts for like 30,000 or so genes. And so here in the background, I've kind of drawn an example of this mapping with all 46 of our chromosomes. And we can see that these might be the genes here. And scientists have mapped out all of the genes that contribute to our genome. And so while in recent history, we've relied heavily on twin and adoption studies to narrow down the heritability of behavioral traits, now that we mapped the entire human genome, we can look at populations which share traits and essentially look at the genes that we expect to be contributing to those traits. And we can compare and contrast those genes. And these studies have given us some really, really fascinating results. As an example, we've discovered that the vast majority of our genes-- I think on the order of 95% or so of our genes don't actually code for proteins. But rather, they regulate how those proteins are coded. So instead of changing the protein, they actually change the context of the protein and when and how it's expressed, so kind of like little if-then statements. If we experience sugar consumption, then we code for the protein hormone insulin. And there's this whole playlist in the biology section that covers gene control and covers this modulatory world of gene expression. So I'm not going to go too deep into it. But it is an important point, especially as we actually see differences in the molecular structure of genes contributing to the heritability of our behaviors. And then even outside of the study of the DNA structure and the gene sequence, we've started discovering other things at this molecular level that are affecting gene expression. And this is an entire new field now concerned with this called epigenetics. And so epigenetics is the study of the changes in gene expression resulting from changes to something other than the DNA sequence. And a classic example of epigenetic influence is methylation, so the addition of methyl groups to the gene. And the addition of these methyl groups can actually make it more difficult for the transcription factors to come in and identify and activate the gene. So the gene essentially isn't expressed, not because the sequence is irritated. But rather because something is inhibiting the activation. And we actually see this phenomenon in rats. So different styles of rat mothering can nearly permanently change the stress response in our offspring due to methylation. So we see our environment causing this methylation, which affects gene expression. And so in a sense, these epigenetic factors are capable of overriding the DNA sequence in determining our behavior. And so these ideas are quite biological compared to the majority of psychology. But molecular genetics and epigenetics really represent the next step in sorting out the heritability of our behavior.