When graphing the phenotypes of a trait controlled by many genes ...

Question

When graphing the phenotypes of a trait controlled by many genes and the environment, the line showing the frequency of each phenotype resembles                   .
a. a horizontal, straight line;
b. a vertical, straight line;
c. the letter T;
d. a bell shape;
e. a circle

Accepted Answer

Welcome back. Here's our next question. When graphing apologetic traits against the fanatic frequency, a bell shaped form is created. What contributes to this result. So we'll start by recalling from our content video that apologetic traits with that polly and genic are traits that multiple genes contribute to the phenotype. So in humans this is things like height. Wait skin color. So we don't just have a single gene, you know, for tall person or short person, we have multiple genes coming together working together to affect the phenotype. So if we did a graph of apologetic trait against how frequent that phenotype is we get. So let's say for example height human height. So we would graph different height values here versus number of people with that height. And we would see a bell shaped curve. So we're going to see, you know, a few number of people that are very short, small number of people that are extremely tall and most of our people are of average height here in the middle. So what what causes this? What contributes to this result? Well, we've got four answer choices. Always a good idea to look through them and see if there's anything we can eliminate right away. And when we do that, we see that choice C says extreme phenotype sis are usually greater in number. But we just looked down at our graph and saw that the extreme phenotype the very short, very tall are the lowest occurrence. So choice C. Cannot be correct. It describes the opposite of what we see in this bell shaped curve. Same with choice D. That says average phenotype are usually smaller in number. But again, as we saw, the average phenotype are the largest number of people in the population. So Choice D also can get eliminated right away. So when we have our choices here, we're looking between Choice A. Which has apologetic traits have continuous variation or be apologetic traits consist of discrete values. Well, apologetic trade because it has multiple genes contributing and it doesn't have. These genes have incomplete dominance. So you don't have a situation where you have a dominant and recessive gene where a dominant gene is masking a recessive gene, you have genes that are contributing in different amounts to the phenotype. So as a result you do have continuous variation because your phenotype can be any value in this range, even a decimal value. So it's not an either or it's not like the p problem where you have a yellow P. Or green P. We don't have yellow green peas, light yellow peas, dark green peas. It's either yellow or green. That would be an example of discrete values. This or that However, an incomplete dominance we have continuous variation because our phenotype can vary over an entire range. So we see that choice be apologetic traits have discrete values is not correct and our answer here is choice a apologetic traits have continuous variation. That's what causes that bell shaped distribution. Thanks for watching. See you in the next video

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