Analyzing Trait Variance - Online Tutor, Practice Problems & Exam Prep

Trait variance is influenced by both genetic and environmental factors, represented mathematically as VP=VG+VE. To isolate genetic variance, maintain a controlled environment while varying genotypes. Conversely, to assess environmental impact, use genetically identical clones in diverse conditions. Understanding these variations is crucial for studying complex traits and their heritability, as they reveal the interplay between genetics and environment in phenotype expression.

Analyzing Trait Variance

Hello, everyone. In this lesson, we are going to be learning about how to analyze trait variants. Okay, everyone. So traits obviously vary. You can have different phenotypes for different individuals for the same particular trait. Now, trait variance can be determined by many factors. It can be determined by genetic and environmental factors. And most of the time, it's going to be both. Both environmental and genetic factors are going to be contributing to the particular phenotype that an individual has. And to understand mathematically which gives which amount of variance, we have this formula:

VP = VG + VE

Where V_P means the variance in the phenotype or the variance in the trait that you were looking at, V_G is going to be the genetic variance, the variance in the genotypes of the individuals. Which types of alleles do they have? How much do they vary across the population? And then V_E is going to be the environmental variance. So how much does the environment vary? How much does that matter towards the phenotype of the individual? Because some genes or some traits are very different. Some traits are determined greatly by the environment. Some traits don't care at all about the environment and are only determined by genetic variance. So, it is very interesting to look at where the variance comes from in a particular trait.

Now, to determine the variation attributed to genetics only, what are you going to control for? Well, if you want to know exactly how much variance only comes from the variance in the genomes, then you should have no variance in the environment. So, you should control for environmental variance. So, the environment should be the same, exactly the same for all of your test subjects, but your test subjects can have different genotypes. So, if you were looking for how much genetic variation contributes to, let's say, stem height in flowers, then what you would do is you would plant multiple seeds of one species in a carefully controlled greenhouse. So, this is going to allow you to have zero environmental variance because they are all in the exact same environment. They all have the exact same environment. They do not vary in their environment, so there is no environmental variance. And, you're going to have multiple seeds from one species. But these genotypes of the seeds vary. So they have genetic variants. So whenever you're looking at the trait or phenotype of stem height and you want to know how much variance in stem height relates to the variance in the genotype, you simply control for the variance in the environment.

Now, what if you wanted to do the exact opposite of that? What are you going to do? Well, to determine the variation attributed to the environment, you must control for genetics. So, how much environmental variation contributes to the stem height of these flowers? You're going to plant multiple genetically identical seeds. So these are going to be clones of one another and then you are going to try out different environmental conditions. So, you're going to allow the environment to vary but not the genotypes of these individuals. So there's going to be no genetic variance and this is because they all have the same genotype. They are clones of one another. So they're all genetically the same. There's no genetic variance. But you could put them in different environmental conditions. Maybe some plants are outside, inside, in the rain, in the sun, in the shade. You can change it up, right? So a representation of these types of experiments can be seen here. So let's look at the first one which is going to be environmental variation. So if you're looking for environmental variation or how much variation in the environment contributes to the phenotype, you need to have all the same individuals. So these are clones of one another. And you guys can see that because there's only one genotype. Only one genotype. And that genotype is the A genotype. So all of these individuals, you guys can see, all of these plants have the exact same genotype. They have the A genotype. They are clones of one another. But each of these individuals is in a unique environment. So, they all have a unique environment. So, maybe the first one here lives in the shade, but it's given a certain amount of water. And then this one here lives in the sun and is given a certain amount of water. Or this one's in the cold, this one's in the heat. Their environment is changed and it's going to see how the phenotype varies. And obviously because the height is different for these individual clones, the environment does have some effect on the variance that we see in plant height. So, yes, the environment in that particular graph does have an effect on the variance in the plant height. If it didn't, if it had no effect, you would see something like this. Where all of the plant heights were the same. What you could glean from that is that there is only genetic variance that matters in the phenotype of these individuals. The environment does not have any control over the expression of plant height. If we had no effect from the environmental variation. That is what it would look like. But our graph is different. So obviously the environment does vary the phenotype a bit.

Now, this one here, we're doing the opposite. This is genetic variation. So how much genetic variation contributes to the variation in the genotype? Now, you guys can see that they all have unique genotypes. All of these genotypes here are unique. We have individuals A, B, C, D, E, F, G, and H. They all have unique genotypes. So they're not genetically the same. They are not clones. But they all have the same environment. All have the same environment. So, for this experiment, V_E equals 0. For the other experiment, V_G equals 0. And they're testing how much genetic variation contributes to phenotype variation and how much environmental variation contributes to phenotype variation. And as you guys can see, the different genotypes do have different heights. So yes, genetic variation also has some effect on phenotype variation. So those are going to be the different types of variation that you can look at for the variation in a trait and remember you can always do this formula to see how much the environment and how much the genetics vary and how they contribute to the variation in the phenotype.

Okay, everyone. Let's go on to our next topic.

Which of the following represent trait variation caused from genetic variation?

• A. V_P
• B. V_G
• C. V_E
• D. V_V

If you wanted to identify what proportion of trait variation is due to the environment, you would do what?

• A. Control for environmental variation
• B. Control for overall variation
• C. Control for genetic variation
• D. Control of phenotypic variation

If you wanted to identify what proportion of trait variation is due to genetics, you would do what?

• A. Control for environmental variation
• B. Control for overall variation
• C. Control for genetic variation
• D. Control of phenotypic variation

Here’s what students ask on this topic:

What is the formula for analyzing trait variance and what do the components represent?

The formula for analyzing trait variance is VP=VG+VE. Here, VP represents the total variance in the phenotype, VG is the genetic variance, and VE is the environmental variance. This formula helps in understanding how much of the observed trait variance is due to genetic differences and how much is due to environmental factors.

How can you isolate genetic variance in an experiment?

To isolate genetic variance, you need to control for environmental variance. This means keeping the environment constant for all test subjects while allowing their genotypes to vary. For example, you could plant multiple seeds of one species in a controlled greenhouse where environmental conditions like light, temperature, and water are kept the same. This way, any observed variance in the phenotype, such as stem height, can be attributed to genetic differences among the seeds.

How can you assess the impact of environmental variance on a trait?

To assess the impact of environmental variance, you need to control for genetic variance by using genetically identical clones. These clones should be exposed to different environmental conditions. For instance, you could plant clones in various environments such as different light, temperature, and water conditions. Since the genotypes are identical, any observed variance in the phenotype, like plant height, can be attributed to environmental differences.

Why is it important to understand the contributions of genetic and environmental factors to trait variance?

Understanding the contributions of genetic and environmental factors to trait variance is crucial for studying complex traits and their heritability. It helps researchers determine how much of a trait is influenced by genetics versus the environment. This knowledge is essential for fields like agriculture, medicine, and evolutionary biology, where it can inform breeding programs, disease prevention strategies, and understanding of natural selection processes.

What would an experiment look like if environmental variance had no effect on a trait?

If environmental variance had no effect on a trait, an experiment would show that all individuals with the same genotype exhibit the same phenotype regardless of environmental conditions. For example, if you planted genetically identical clones in different environments and observed no variation in their height, it would indicate that the environment does not influence this particular trait. This would mean that the trait is solely determined by genetic factors.