Floral traits in plants often play key roles in diversification, in that slight modifications of those traits, if genetically determined, may quickly lead to reproductive restrictions and evolution. Insight into genetic involvement in flower formation is often acquired through selection experiments that expose realized heritability. Lendvai and Levin (2003) conducted a series of artificial selection experiments on flower size (diameter) in Phlox drummondii. Data from their selection experiments are presented in the following table in modified form and content.
Assuming that the realized heritability in phlox is relatively high, what factors might account for such a high response?

Question

Floral traits in plants often play key roles in diversification, in that slight modifications of those traits, if genetically determined, may quickly lead to reproductive restrictions and evolution. Insight into genetic involvement in flower formation is often acquired through selection experiments that expose realized heritability. Lendvai and Levin (2003) conducted a series of artificial selection experiments on flower size (diameter) in Phlox drummondii. Data from their selection experiments are presented in the following table in modified form and content.

Assuming that the realized heritability in phlox is relatively high, what factors might account for such a high response?

Table showing mean flower diameter in millimeters for control, selected parents, and offspring across 1997-1999 in a selection experiment.

Assuming that the realized heritability in phlox is relatively high, what factors might account for such a high response?

Accepted Answer

Hello everyone. Here's our next question to identify the realized heritability. Which equation is utilized by evolutionary biologists? Well, we need to think about and recall what realized heritability is realized heritability also called narrow sense Heritability is the proportion of fanatic variation in a population attributable to additive gene effects. So when you look at a population and look at its different phenotype, what proportion of that variation is due to multiple genes working together? This is as compared to broad sense heritability, which is the proportion of genetic variation due to all genetic causes. So additive genetic effects, dominant and recessive genetic effects and episodic recessive. Um And the reason we distinguish between these two is that the narrow sense heritability B is easier to estimate, easier to examine a population and estimate it versus broad sense. And it also gives a good estimate of broad sense heritability. So it's easier to calculate and can give us a good sense or a good estimate for that broad sense heritability. So we usually look at this narrow sense heritability and as our question indicates, we have an equation that's used to calculate that. And looking at the answer choices we can recall from our content video that this is choice a breeder's equation. So let's just look over that equation briefly. Just to recall how that is used to identify, realize charitable itty. We have this breeder's equation is delta Z. Equals H squared delta S. Um The H squared value here is our realized heritability. So the proportion of trade variability due to additive genetic effects. We almost never have all the things we need to actually calculate the number. Um It must be estimated from the resemblance of relatives. So looking at parent and offspring and siblings, what is the genetic variation among those relatives? And that can be used to estimate the H. Squared value. And then this equation, the S value is the selection differential which is the association between the trade value and fitness. So that'll be negative if a lower trade value, say lower height is associated with greater fitness positive if a greater trade value is associated with greater fitness. And then finally DELTA Z. Z. Is the mean value of a trait in the population. So what's the mean height? What's the main weight? And then delta Z. Would be the change that you see in that means in one generation. So this is the breeders breeders equation and can be used to estimate realized or calculate an estimated value for realized heritability. Let's look at our other answer choices here to see why they're incorrect. A choice B is hardy Weinberg equation and the hardy Weinberg equation is the one that relates to the frequency of different genotype, different alleles in a population. And it's the one that states that the frequency of genotype and a population or the frequency of the distribution of alleles in a population. Excuse me, will remain constant over generations absent any disturbing influence or absent any natural selection or anything like that. So it has to do with a little frequency remaining constant in a population. But it's not our answer choice. Not used to calculate realized heritability. So we'll cross that out. Joyce C says linkage disequilibrium equation. And this is used to calculate uh and determining how often alliances occur together um as to see to see whether that's occurring more frequently than chance. Um This is used to help us determine whether or not aliens are on the same chromosome. So how often alleles occur together is what that equation is used for but not a correct answer. And finally, Choice D. Broad sense heritability equation. And again we talked about broad sense being the proportion of genetic variation due to all genetics causes. So that equation is going to be big. H squared equals V. G. Which is a variation due to genetic causes over V. P. Which is the fanatic variation in the entire population. But again we discussed that realized heritability uh is the same as narrow sense heritability which is that variation due just to additive effects, not the variation due to all genetic causes. So that's why choice D. Is not correct. So to identify the realized heritability, which equations used by evolutionary biologists choice a breeder's equation. See you in the next video

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Key Concepts

Heritability

Artificial Selection

Evolutionary Potential