Genes and Environment: Study with Video Lessons, Practice Problems & Examples

Introduction to Genetics

Alright, so this video is going to be a little introduction to genetics and we're going to begin by just going over some important terminology. So we're going to start with genes, and genes are basically the biological units of heredity that are passed from parents to offspring. And genes are basically segments of DNA, so genes are located on DNA. Now, I'm sure you know what DNA is, but this is basically the molecule that actually holds genetic information. And DNA gets organized into chromosomes.

So chromosomes are these thread-like structures that actually organize and package DNA, and humans have 23 pairs of chromosomes. So, if we look at our image here, we have our chromosome in that kind of classic X-shaped structure, and the chromosome is made up of DNA. And then you can see we have this little pink segment on our DNA, and that would be a gene. Okay? So that is the relationship between genes, DNA, and chromosomes.

Now, when we are thinking about genetics, we're always thinking about 2 different things: genotype and phenotype. So, genotype is the complete genetic makeup of an organism. So this is literally like what genes does this person have? It's important to be aware that most traits are what we call polygenic, which means that they are influenced by more than one gene. And that's true of physical characteristics like hair color, for example, but this is especially true of behavioral characteristics, especially more complex behaviors.

So, for example, we have found an association between the DRD4 gene, which impacts dopamine receptors, and the behavior of novelty seeking. However, the DRD4 gene isn't like the novelty-seeking gene. That would be kind of misleading because there are a lot of genes associated with novelty seeking. It's a very complex behavior. So even though we have found that association and it seems to be true, there are other genes at play.

So, if you ever see a clickbait article that's like, we found the gene for autism or the gene for ADHD. No, they didn't. They might have found one of them, but that's a very misleading way of talking about it because most traits are polygenic. Alright. So that is genotype.

We also think about phenotype, which are the actual observable characteristics of the person or animal. So this includes things like physical characteristics, like eye color, hair color, mental qualities, like IQ, for example, and behavior. So that could be self-regulation, aggression, novelty-seeking, addictive tendencies, you know, any behavior that you can observe. Now, the phenotype is often the result of the interaction of genes and the environment. So, for example, a person could have a gene that is associated with depression, but let's say they grow up in a really supportive environment.

Okay? That gene might never actually become active and might never manifest in the observable quality of depression. But let's say we have a person who has a gene that we know is related to depression, and they grow up in a really challenging environment. Maybe they grow up in poverty or under abusive parenting or something like that. In that case, we might see that gene become active and then depression might actually manifest.

So, we're always thinking about the interaction of genes and the environment, and how that is going to impact phenotype. And we are going to talk about that a little bit more in our next video coming up about heritability. Alright, so that is our introduction to genetics, and I will see you guys in our next one. Bye bye.

Genes and Environment Example 1

Alright, so here we have a list of the different units of organization of genetic material and we're going to be arranging them from smallest to largest. So if we're thinking about the smallest out of these three, it's going to be genes, right? Because genes are literally tiny segments of our DNA. So genes are the smallest and then DNA would be the next largest. That's the actual molecule that contains genetic material.

Genes are just like a little piece of our DNA basically, and then DNA gets organized and packaged into chromosomes which are kind of the largest unit. Alright. So genes are the smallest unit followed by DNA, and then chromosomes are the largest unit. Alright. There you have it.

The __________ is a genetic makeup of an individual for a specific trait.

• A. Genotype.
• B. Phenotype.

True or False: if false, choose the answer that best corrects the statement.

Genotypes can be visible to the unaided eyes, while phenotypes cannot.

• A. True.
• B. False; phenotypes can be visible to the unaided eye, while genotypes cannot.
• C. False; both genotype and phenotype are visible to the unaided eye.
• D. False; neither genotype nor phenotype are visible to the unaided eye.

Heredity

This video, we're going to be talking about heredity, and a really important concept here is going to be heritability, which is basically how much variation in phenotype across people is due to differences in genotype. And what that basically means is that when we are seeing different behaviors or mental qualities across people, we are asking how much of that variation seems to be due to genetics, basically. And so we actually calculate heritability as a proportion between 0 and 1, and we call this a heritability estimate. So, if we have a heritability estimate of 0, then what we are basically saying there is that genes do not contribute to individual differences on that trait at all. In contrast, if we had a heritability estimate of 1, we are basically saying that only genes contribute to individual differences on that trait.

Now, I would encourage you within the field of psychology, at least to kind of think about 0 and 1 as kind of theoretical limits. They almost never come up in psychological research. Typically, the values that we're going to see in psychological research are going to range from about 0.3 to about 0.6. So, just to give you a more concrete example of a heritability estimate, let's say we ran a study and found, you know, for IQ, we have a heritability estimate of 0.5. What we are basically saying there is that 50% of the variability that we see across people in IQ is due to genetics, and about 50% of the variability seems to be due to the person's environment.

So that's kind of the idea with heritability estimates. Now, in psychology, we do not often study actual genes. We're not geneticists, we're psychologists, right? So psychologists have come up with some pretty interesting study designs to kind of help us tease apart if genes or environment seems to be playing a bigger role. So we tend to study heredity in 3 major ways.

So, first, we very often study pairs of twins. So, when we are thinking about twins, of course, you can either have monozygotic twins or identical twins, which we are just going to abbreviate as MZ twins, and MZ twins share 100% of their genetic material. Okay, so these twins share all of their genes and if they are being raised together, they also share all of their environment as well, right? Now, in contrast, you can have dizygotic or fraternal twins, which we're going to abbreviate as DZ twins. And DZ twins, like any other sibling pair who share parents, share 50% of their genetic material.

So, assuming that they are being raised together they share half of their genes and all of their environment. So we can do studies basically contrasting MZ twins and DZ twins to see if genes or environment seem to be playing a bigger role in things like behaviors and mental qualities. So, for example, if we find that MZ twins are more similar on aggression scores compared to DZ twins, then that is evidence that there's some kind of genetic component for aggression. That's how we would do those types of studies. Now we can take this one step further and we can also study MZ twins who have been separated at birth, and this gives us a really unique situation where you have 2 people who share 100% of their genetic material but almost none of their environment, maybe like a basic cultural environment, but aside from that, none of their environment is shared, and so you can basically try and see if these twins are similar to each other or different from each other.

You can also compare MZ twins who were separated at birth with DZ twins who were separated at birth, to see if they are more or less similar to each other. One really famous study that did this found that monozygotic twins who had been separated at birth, their IQ scores correlated at 0.7, which is really, really high compared to DZ twins who had been separated at birth, and their IQ scores correlated at, like, 0.3. So that's significantly lower. Right? So that gives us pretty strong evidence that there seems to be a strong genetic component to IQ because we saw how similar those MZ twins were and they, of course, share their genetic material.

So, we can do twin studies in kind of 2 different ways. We can also study adoptees and their birth and adopted parents. So with adoptees, what you have is that they're going to be sharing their DNA with their birth parents but none of their environment, and then they're going to share their environment with their adopted parents but none of their DNA. So we can look to see if they are more similar to their birth parents or to their adopted parents to get a sense if genes or environment seem to be playing a stronger role in their behaviors or mental qualities. So the big idea behind all of these study designs is basically to help us figure out what traits are more influenced by genetics and which traits seem to be more influenced by environment.

That's kind of what we're getting at here. And we are always acknowledging that there's always going to be an interaction of genes and environment as well. Alright. So that is how psychologists study heritability, and I will see you guys in our next video. Bye bye.

Genes and Environment Example 2

Okey dokey. So here we have a number line representing how much genes contribute to the expression of a trait. So, we're going to fill in the blanks here, basically saying if the trait is somewhat, totally, or not at all controlled by genetics. So if we're thinking about our limits of 0 and 1, if we start over at 0, what we're basically saying here is that genes are not contributing to the expression of the trait, right? So it's going to be not at all.

What we're basically saying here is that the environment is doing all of the work and genes are not doing anything regarding that trait. Now over here at 1, on kind of the other side of our limit, what we're saying here is that only genes are contributing to the expression of that trait, right? So it would be totally. So basically here the environment does not play a role at all and it's all going to be genetics. And then right here at 0.5 it's going to be somewhat genes, right?

So if we were to have a heritability estimate of 0.5 we're basically saying that both genes and environment seem to be contributing to the expression of that trait just about equally. Alright, there you have it and I'll see you guys in the next one. Bye bye.

Why are studies with twins useful in psychology?

• A. They allow researchers to “control” for genetics or the environment.
• B. They allow researchers to work with twice as many subjects.
• C. They allow researchers to have a control group.
• D. They allow researchers to have an experimental group.

Note About Heredity

I wanted to make a quick video just clearing up some common misconceptions that students have when they first learn about heritability. So, because of the way that we study heritability in psychology, it's important to keep three things in mind. The first is that heritability is an abstract concept. But like I mentioned, with the way that we study heritability in psychology, we are usually not identifying specific genes that contribute to a trait. So, even if we find really high heritability estimates for aggression or IQ, it does not mean that we have found the genes that contribute to those things, right?

All it means is that we now have evidence that there is a strong genetic component to that trait, that's all that that means. So heritability is abstract. Another really important thing to keep in mind is that heritability is a population-level concept. So what we're doing is basically examining the role of genetics in trait variation within a population. Okay?

Not within an individual. So if we were to find a heritability estimate of 0.6 for IQ, that does not mean that I, as an individual, have a heritability estimate of 0.6 for IQ. It does not mean that you have a heritability estimate of 0.6 for IQ. It means that, in the population on average, we are seeing a heritability estimate of 0.6. So, it is very important to keep that in mind anytime you are interpreting research that involves heritability estimates.

And then finally, one last important thing to keep in mind is that heritability is not fate. So, we know through lots of research that trait expression can be influenced by a number of things in a person's environment, and that includes things like interventions and therapy, but really anything in somebody's environment can affect the expression of traits. So even if you have a genetic predisposition for something like depression or addiction, that does not mean that that will necessarily manifest. Genes can actually get turned on and off by things in a person's environment. We don't have to get into the biology of how that actually happens, but just be aware that heritability is not fate.

Alright, so those are three really important things to keep in mind anytime you are thinking about heritability. It is abstract, it is a population-level concept, and it is not fate. Alright, thanks guys, and I'll see you in the next one. Bye bye.

Genes and Environment Example 3

Okay. So based on what we know about genes and heritability, what is wrong with the statement? Quote, "His mother was an alcoholic, so he probably inherited the gene and will be one too." End quote. So, not the most accurate. Let's go through our answer choices and see how we can refine that a little bit.

So, Option A reads that many traits, especially those involving complex behavior, are polygenic. And that is absolutely true, right? And in this quote here, they're saying that he probably inherited the gene as though there's only one gene that contributes to something as complex, you know, biologically and socially, behaviorally complex as alcoholism. That is very unlikely; this is likely a polygenic issue. So Option A is looking pretty promising.

Option B reads that heritable traits cannot be passed from mother to son, but that's not true. Right? We know that obviously, heritable traits do get passed down from parents to their children, so Option B is incorrect. And then Option C reads that heritability is not fate. Trait expression can be influenced by many factors including a person's environment, and that is also true, right?

Even if this person had inherited some genes that we know are associated with alcoholism, it does not mean that we will necessarily see the expression of those genes. His environment could have altered the way that those genes are going to get expressed. So Option C is also accurate. So it looks like our answer is going to be Option D: both A and C are true.

Many traits are polygenic and heritability is not fate. Alright, guys, I'll see you in the next one. Bye-bye!